JP2014209585A - Design method, design program of tandem thin film solar cell and tandem thin film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tandem thin film solar cell suitable to the environmental conditions of an installation place easily.SOLUTION: A design method of a tandem thin film solar cell comprises: a step of calculating the optical characteristics information of each photoelectric conversion unit independently from the dependence on the shape of other layer and electrical dependence; a step of calculating power loss of a design structure by using the electrical characteristics information of each photoelectric conversion unit; and a step of comparing the power loss with a predetermined threshold and determining whether or not the power loss falls within an allowable range. When the power loss is less than a predetermined threshold, the design structure is considered as the final structure and the design is ended. When the power loss is larger than a predetermined threshold, a step of determining a new design structure by adjusting at least one of the optical properties information, electrical properties information, and shape information is performed, and then the calculation step is repeated.

Description

  The present invention relates to a tandem thin film solar cell design method, a design program, and a tandem thin film solar cell.

Recently, global warming caused by discharge of CO ₂ with the use of fossil fuels, such as radioactive contamination caused by accidents and radioactive waste of a nuclear power plant, the interest in global environment and energy has been increasing rapidly. Under such circumstances, solar cells that are photoelectric conversion elements using incident light of the sun are expected from all over the world as inexhaustible and clean energy sources.

  As a form of the solar power generation system using this solar cell, there are various scales and types from several watts to several thousand kW. For example, many systems exist, such as a form in which the power generation energy of the solar cell is stored using a battery and a form in which the output energy of the solar cell is poured into a commercial system using a DC-AC converter.

As a conventional photovoltaic power generation system for generating power by installing a solar cell on the roof of a house or building, there is a grid-linked photovoltaic power generation system. This grid-connected photovoltaic power generation system performs linked operation by converting the DC power output from the solar cell module into AC power using an inverter circuit and using it as a power source for the facility, while supplementing the shortage from the grid power network Is.
If surplus power is generated, it is also possible to sell power (reverse power flow) to the power company using the grid power network. Although there are small differences such as the size of the load and the presence or absence of electricity sales, from general household roofing type (~ several kW) to mega solar (large scale solar power generation facilities: ~ several MW), this is generally There are many usage forms. Therefore, in terms of the comparison with the grid power, in the photovoltaic power generation system, the power generation cost is often asked as the capacity index. In general, the power generation cost is simply expressed by the following equation (1).

  Traditionally, technology development to reduce power generation costs has reduced the number of numerator items in Equation (1), such as initial investment costs (panel costs, installation costs, etc.) and maintenance costs (extension of panel life, remote monitoring, etc.). It has been mainly addressed. Improvement of photoelectric conversion efficiency is a typical example of panel cost and installation cost reduction. Lifetime power generation is the total amount of power generated during the useful life under the environmental conditions of the place where it is installed.

  However, the photoelectric conversion efficiency has reached the region close to the theoretical limit (the theoretical limit is 28% for the crystalline silicon solar cell, 25% for the developed product and 21 to 23% for the mass-produced product), and only the improvement of the photoelectric conversion efficiency is achieved. The current situation is that the cost reduction due to the process is not being realized due to the complexity and cost increase of processes and equipment, the increase in material costs, and the increase in development costs.

On the other hand, the development of the denominator term in equation (1), especially the lifetime power generation, has not progressed so much. This is mainly
(1) It is difficult to predict environmental conditions at the installation location.
(2) Few margins for optimization due to limitations due to materials and costs.
(3) There are many production processes that are collectively optimized, and local changes in the process are difficult.
(4) It is difficult to predict the characteristics of a solar cell that has undergone local changes, and prototypes are often required.
(5) Not suitable for high-mix low-volume production.
This is because there are such restrictions.

Therefore, in general, the assumed power generation amount of the solar power generation system is generally determined as follows.
(11) Photoelectric conversion efficiency measured under standard test conditions (STC condition: Standard Test Cell condition, spectrum shape is AM1.5, solar radiation is 1.0 kW / m ² normal incidence, solar cell temperature is 25 ° C.) Determine the module rating.
(12) Set correction terms such as temperature characteristics and inverter efficiency.
(13) The amount of solar radiation at the installation point is determined by the New Energy and Industrial Technology Development Organization (NEDO) and the database of solar radiation provided by the Japan Meteorological Agency.
(14) Calculate the amount of power generation based on the above conditions (simple power generation amount = solar radiation amount x rating x correction term).

Moreover, the function of the element which comprises a photovoltaic cell is divided roughly into the following three.
(A) photoelectric conversion function (b) light confinement function (c) conductive function

  The photoelectric conversion function of (a) is a function that converts photons into electron-hole pairs. In general, a semiconductor pn junction is often used. The light confinement function (b) is a function that allows photons incident on the cell to be converted into electron-hole pairs without waste, such as reducing surface reflection and increasing the optical path length. In general, fine irregularities are often formed on the substrate surface or transparent conductive film, and a diffusible reflector is often provided on the back surface of the substrate. The conductive function of (c) is a function of guiding the generated electron-hole pair to the electrode. In general, a comb electrode or a transparent conductive film is often used.

  One cause of the conventional limitations (1) to (5) is that these three functions are collectively optimized under STC conditions. For example, in a typical tandem-type thin film silicon solar cell, a front transparent conductive film as a first electrode layer, and a first p-type semiconductor film, a first i-type semiconductor film, and a first n-type semiconductor film are stacked from the front transparent conductive film side. The first photoelectric conversion unit, the second photoelectric conversion unit in which the second p-type semiconductor film, the second i-type semiconductor film, and the second n-type semiconductor film are stacked from the first photoelectric conversion unit side, and the back transparent conductive film that is the second electrode layer , And a back reflector are stacked on a light-transmitting substrate.

The layers constituting such a tandem-type thin film silicon solar cell are classified into the above functions (a) to (c) as follows.
(A) Photoelectric conversion function: first photoelectric conversion unit, second photoelectric conversion unit (b) light confinement function: front transparent conductive film, back reflector (c) conductive function: front transparent conductive film, back transparent conductive film, back reflector

  However, since each layer has a dependency on the shape of the ground and electrical characteristics (work function, etc.), the prototype and the process conditions that can clear the dependency have been searched in the past. Therefore, it is difficult to design each function of (a) to (c) independently, and as a result, restrictions as shown in (1) to (5) occur.

  On the other hand, we focused on the fact that the spectral shape, the angle of solar radiation, the amount of solar radiation, and the temperature of the solar battery cells change every moment depending on the environmental conditions of the installation site. By using solar cell design, it is possible to maximize the amount of power generated throughout the lifetime. For example, in the case of a multi-junction solar cell such as a tandem-type thin film silicon solar cell, solar cells having different spectral sensitivities are connected in series. Therefore, if the photocurrents of the solar cells do not match, power loss occurs. End up. Therefore, it can be expected that the lifetime power generation amount is larger than the rated output obtained under the STC condition by customizing the spectral sensitivity of each solar battery cell that is optimal not based on the STC condition but on the spectral condition of the installation point.

  For this reason, for example, as disclosed in Patent Document 1, a method for optimizing the spectral sensitivity and photocurrent of each solar cell by changing the i-layer thickness of each solar cell of the tandem-type thin film silicon solar cell according to the installation latitude is proposed. Has been.

JP 2006-165076 A

  However, according to the technique of the above-described Patent Document 1, it takes time and labor to actually manufacture a standard cell used as a reference and to perform outdoor exposure by making a module as a prototype, and (3) and (4) described above. ) Was still a problem.

  The present invention has been made in view of the above, and the design of a tandem thin-film solar cell that can be easily designed at low cost and can be easily designed as a tandem thin-film solar cell suitable for the environmental conditions of the installation site. The object is to obtain a method, a design program and a tandem thin film solar cell.

  In order to solve the above-described problems and achieve the object, a design method for a tandem-type thin film solar cell according to the present invention includes a transparent electrode layer and a plurality of semiconductor films having different impurity doping conditions on a translucent substrate. And a plurality of photoelectric conversion units are stacked in this order, and are provided between the translucent substrate and the transparent electrode layer as a connection layer that eliminates the dependency on characteristics between the respective layers. A first connection layer that eliminates the substrate shape dependency, and the first photoelectric conversion provided between the transparent electrode layer and the first photoelectric conversion unit on the transparent electrode layer side among the plurality of photoelectric conversion units. A second connection layer that eliminates electrical dependence between the unit and the transparent electrode layer; and a third connection that is provided between the semiconductor films having different impurity doping conditions to eliminate the electrical dependence between the semiconductor films. A layer comprising A method of designing a tandem thin film solar cell in which sunlight is incident from the conductive substrate side, wherein the first step of determining environmental information of an installation location of the tandem thin film solar cell including information on solar radiation, and the light transmission The shape information and optical property information about the conductive substrate, the transparent electrode layer, the plurality of photoelectric conversion units and the connection layer, and the electrical property information about the transparent electrode layer, the plurality of photoelectric conversion units and the connection layer Second step of determining the design structure of the tandem-type thin film solar cell to be designed, and each photoelectric conversion unit for sunlight incident from the translucent substrate side using the optical property information and the shape information A third step of calculating the optical property information of the design, and using the electrical property information, the optical property information, and the information on the solar radiation, the electrical property of the design structure A fourth step of calculating an information, a fifth step of calculating a power loss of the design structure using the electrical characteristic information, and comparing the power loss with a predetermined threshold and the power loss is within an allowable range. A sixth step of determining whether or not, in the sixth step, when the power loss is equal to or less than the predetermined threshold, the design is finished with the design structure as a final structure, and the sixth step When the power loss is larger than the predetermined threshold value, a seventh step of determining a new design structure by adjusting at least one of the optical property information, the electrical property information, and the shape information is performed. After the execution, the third and subsequent steps are repeatedly performed.

  According to the present invention, it is possible to easily design a tandem-type thin film solar cell suitable for the environmental conditions of the installation location and obtain it at low cost.

FIG. 1 is a cross-sectional view of a principal part showing a schematic configuration of a tandem-type thin film silicon solar battery cell according to a first embodiment of the present invention. FIG. 2 is a flowchart showing a flow of the solar cell design method according to the first embodiment of the present invention. FIG. 3 is a configuration diagram illustrating a schematic configuration of a design apparatus that executes the solar cell design method according to the first embodiment of the present invention. FIG. 4 is a characteristic diagram showing the external quantum efficiency of the solar battery cell obtained by light propagation calculation and the measured external quantum efficiency of the solar battery cell. FIG. 5 is an image showing a fisheye image of the sky photographed on a horizontal plane (corresponding to a solar cell module placed vertically) in Amagasaki City, Hyogo Prefecture. FIG. 6 is a characteristic diagram showing the relationship between the solar radiation spectrum intensity at a certain time in Amagasaki City and the actual solar radiation spectrum intensity calculated using the sky description parameter and the sky shielding information. FIG. 7 shows the calculation of cumulative power loss due to mismatch of photocurrents between photoelectric conversion units in a two-junction tandem thin-film solar cell in which the number of junctions of the photoelectric conversion units is two (two photoelectric conversion units are stacked). FIG. FIG. 8 shows the calculation of cumulative power loss due to mismatch of photocurrents between photoelectric conversion units in a three-junction tandem thin-film solar cell in which the number of junctions of the photoelectric conversion units is three (three photoelectric conversion units are stacked). FIG. FIG. 9 is a flowchart showing the flow of the solar cell design method according to the second embodiment of the present invention. FIG. 10: is a flowchart which shows a cell current calculation process among the flows of the design method of the photovoltaic cell concerning Embodiment 3 of this invention. FIG. 11 is a characteristic diagram showing the dependence of the photocurrent on the solar radiation intensity calculated using the internal loss and the dependence of the actually measured photocurrent on the solar radiation intensity. FIG. 12 is a histogram showing the ratio of each solar radiation amount period to the total solar radiation energy for one year in the temperate region. FIG. 13 is a histogram showing the ratio of the period of each solar radiation amount to the total solar radiation energy for one year in the tropical region. FIG. 14 is a histogram showing the contribution ratio of each solar radiation amount to the total solar radiation energy for one year in the desert region.

  EMBODIMENT OF THE INVENTION Below, the design method of a tandem-type thin film solar cell concerning this invention, a design program, and embodiment of a tandem-type thin film solar cell are described in detail based on drawing. In the following, a two-junction tandem-type thin film silicon solar cell is described as an example. However, the present invention is not limited to this embodiment, and can be appropriately changed without departing from the gist of the present invention. is there. In the drawings shown below, the scale of each member may be different from the actual scale for easy understanding. The same applies between the drawings.

  The environmental information used in the present specification is a group of information mainly composed of two types of information, mainly physical aspects and mainly meteorological aspects. The physical aspect information includes, for example, position information including latitude and longitude, installation direction of the solar cell module, installation inclination angle, sky shielding information by blocking the sky by a building, and the like. The sky shielding rate is a horizontal plane solid angle projection rate, and can be said to be the ratio of the area of the building to the screen when a sky photograph is taken with a fisheye lens. Information on the meteorological aspect includes, for example, solar radiation intensity information, temperature, wind direction, wind speed, total cloudiness, and cloudiness around the sun. The solar altitude and solar orientation are also included in the environmental information, but these can be calculated from the position information and time information. In this specification, a group of information mainly related to meteorological aspects such as solar altitude, solar orientation, and cloudiness is referred to as a sky description parameter.

  Here, the solar radiation intensity information is defined as model information of “movement of solar radiation intensity in one year under the average weather conditions created from past data (a function of time of solar energy incident amount per unit area)”. . Also, the solar radiation spectrum information is obtained from the solar radiation intensity information, the installation orientation of the solar cell module, the installation inclination angle, and other environmental information, and is a model of “one-year movement of solar radiation intensity for each wavelength on the inclined surface of the solar cell module”. Defined as information. The solar radiation spectrum information takes into account the solar altitude, cloudiness, shielding information, and the like, and refers to the light itself incident on the inclined surface of the solar cell module. That is, it is a function of Int (λ) time used in the cell current calculation step (step S140) described below.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view of a principal part showing a schematic configuration of a tandem-type thin film silicon solar battery cell (hereinafter referred to as a solar battery cell) according to the first embodiment of the present invention. A tandem integrated thin-film solar cell in which a plurality of thin-film solar cells are electrically connected in series or in parallel is sealed with a sealing material between the light-receiving surface side protection member and the back surface side protection member, A solar cell module used in the photovoltaic system is configured (not shown).

  The solar cell according to the first embodiment is made of glass or the like, and has a front surface as a first electrode layer (transparent electrode layer) having translucency on a translucent substrate 1 having a flat or fine uneven surface. A transparent conductive film 2, a first photoelectric conversion unit 11 composed mainly of amorphous silicon and mainly absorbing short-wavelength light, and composed mainly of microcrystalline silicon containing a crystalline component and mainly composed of a long wavelength. A second photoelectric conversion unit 12 that absorbs light on the side, a back transparent conductive film 9 as a second electrode layer, and a back reflector 10 are sequentially stacked. In this solar cell, sunlight enters from the translucent substrate 1 side.

  In the present embodiment, a glass substrate is used as the translucent substrate 1. On the surface of the translucent substrate 1 on the front transparent conductive film 2 side, fine irregularities are formed, which bears a light confinement function. In the first photoelectric conversion unit 11, a first p-type semiconductor film 3, a first i-type semiconductor film 4, and a first n-type semiconductor film 5 are laminated in this order from the front transparent conductive film 2 side. In the second photoelectric conversion unit 12, the second p-type semiconductor film 6, the second i-type semiconductor film 7, and the second n-type semiconductor film 8 are laminated in this order from the first photoelectric conversion unit 11 side.

  The above structure is the same as that of a conventional general solar battery cell. In the solar battery cell according to the first embodiment, the layers after the front transparent conductive film 2 (front transparent conductive film 2, first photoelectric conversion). Unit 11 and second photoelectric conversion unit 12), the first connection layer 21 for relaxing / resolving the structural dependence on the surface shape of the translucent substrate 1, the translucent substrate 1, the front transparent conductive film 2, It is newly provided between. Here, the surface shape of the translucent substrate 1 is the shape of the surface on the front transparent conductive film 2 side. The structure dependence on the surface shape of the translucent substrate 1 is determined by reflecting the surface shape of the translucent substrate 1 on the shape of the layers after the front transparent conductive film 2 and the structure of the layers after the front transparent conductive film 2. A change in optical and electrical characteristics.

  Further, in the solar cell according to the first embodiment, the second connection layer 22 for relaxing and eliminating the electrical dependency between the first p-type semiconductor film 3 and the front transparent conductive film 2 of the first photoelectric conversion unit 11. Is newly provided between the first p-type semiconductor film 3 and the front transparent conductive film 2 of the first photoelectric conversion unit 11. The electrical dependence between the first p-type semiconductor film 3 and the front transparent conductive film 2 of the first photoelectric conversion unit 11 is determined by the conductive / electrical connection between the first p-type semiconductor film 3 and the front transparent conductive film 2. It means change.

  In the solar cell according to the first embodiment, the third connection layer for relaxing and eliminating the electrical dependence between the first p-type semiconductor film 3 and the first i-type semiconductor film 4 of the first photoelectric conversion unit 11. 23 is newly provided between the first p-type semiconductor film 3 and the first i-type semiconductor film 4 of the first photoelectric conversion unit 11. The third connection layer 23 will be described in detail in the second embodiment. The electrical dependence between the first p-type semiconductor film 3 and the first i-type semiconductor film 4 means a change in electrical conductivity and electrical connection between the first p-type semiconductor film 3 and the first i-type semiconductor film 4.

  This solar battery cell can be manufactured by sequentially laminating each of the above layers using a conventionally known plasma CVD method or sputtering method.

  Next, in the solar cell according to the first embodiment, an optimization design method for designing an optimal structure with respect to the solar spectrum of the installation location of the solar cell (solar cell module) will be described. The electrical characteristics of the solar battery cell are expressed by an open circuit voltage Voc, a short circuit current Jsc, a fill factor FF (Fill Factor), and a photoelectric conversion efficiency η composed of these products. The lifetime power generation amount is represented by integrating the product of the amount of solar radiation at a given time, the deterioration rate γ, and the photoelectric conversion efficiency η for a predetermined period, for example, a predetermined installation year.

  FIG. 2 is a flowchart showing a flow of the solar cell design method according to the first embodiment of the present invention. The solar cell design method according to the first embodiment includes an initial structure determination step (step S110), an optical property calculation step (step S120), a solar radiation spectrum calculation step (step S130), a cell current calculation step (step S140), It has a cell electrical characteristic calculation step (step S150), a cumulative power loss calculation step (step S160), an optimization determination step (step S180), and a structure information adjustment step (step S200).

  FIG. 3 is a configuration diagram illustrating a schematic configuration of the design apparatus 100 that executes the solar cell design method according to the first embodiment of the present invention. This design apparatus 100 is a computer that performs the above-described steps to design a solar battery cell, and a general computer can be used. Note that dedicated hardware may be used for the design apparatus 100. The design apparatus 100 starts a software (solar cell design program) installed therein to perform a predetermined calculation to design a solar cell.

  The design apparatus 100 according to the present embodiment includes an input device 110, a display device 120 such as a liquid crystal monitor, a central processing unit 130, a storage device 140, and an output unit 150. In the design apparatus 100, the input device 110, the display device 120, the central processing unit 130, the storage device 140, and the output unit 150 are connected via a bus line 160.

  The input device 110 includes a keyboard, a mouse, and the like, and a user input unit 111 that can input various data, and an external storage medium input unit that can input various data by reading information from the external storage medium. 112. The external storage medium input means 112 may input various data by reading information from any external means such as the Internet, not limited to the external storage medium.

  The input device 110 inputs instruction information input from a designer (a user of the design device 100). The input device 110 receives execution instruction information for various programs, instruction information for displaying various data on the display device 120, instruction information for outputting various data to the output device, and the like. The instruction information input to the input device 110 is sent to the central processing unit 130 for processing and stored in the storage device 140. The display device 120 displays various data on the display device 120 based on an instruction from the central processing unit 130.

  The central processing unit 130 is an information processing device such as a CPU (Central Processing Unit). The central processing unit 130 designs solar cells using a design program that is a computer program and various data. The storage device 140 includes a main storage device 141 and a secondary storage device 142.

  The main storage device 141 mainly stores a control program and the like used when designing solar cells. As the control program, for example, an optical characteristic calculation processing program 161, an electric characteristic calculation processing program 162, a power loss calculation processing program 163, an optimum determination processing program 164, a structure information adjustment processing program 165, an output processing program 166, and the like are stored. . The main storage device 141 is a storage device such as a ROM (Read Only Memory) or a RAM (Random Access Memory). The secondary storage device 142 includes an information storage unit including an environment information storage unit 171 and a solar cell structure information storage unit 172. The environment information storage unit 171 stores environment information. The solar cell structure information storage means 172 is a solar cell structure used for the design of the solar cell, such as an initial solar cell structure to be optimized or a solar cell structure optimized under STC conditions. Remember.

The design program executed by the design apparatus 100 is loaded into a work area on the main storage device, and these are generated on the main storage device. For example, the design program stored in the ROM in the main storage device 141 is loaded into the RAM in the main storage device 141 via the bus line 160. The central processing unit 130 executes a design program loaded in the RAM.
Specifically, in the design apparatus 100, the central processing unit reads out the design program from the ROM in accordance with an instruction input from the input device 110 by the user, develops it in the program storage area in the RAM, and executes various processes. The central processing unit 130 temporarily stores various data generated in the various processes in a data storage area formed in the RAM. The execution results of various processes are displayed on the display device 120 and are output to the output device in accordance with an instruction input from the input device 110 by the user.

  Below, the design method of the photovoltaic cell concerning Embodiment 1 is demonstrated. Here, a method for designing the structure of the solar battery cell including the first connection layer 21 and the second connection layer 22 will be described. A method for designing the structure of the solar battery cell including the third connection layer 23 will be described in the second embodiment. The following processing is created as a series of programs and executed by the design apparatus. First, in the initial structure determining step (step S110), the initial structure of the solar battery cell that is the source of optimization is set and determined. In this step, for example, a cell structure optimized under STC conditions (AM1.5 spectrum) may be used as the initial structure.

  First, a designer (a user of the design apparatus 100) inputs design program start information to activate the design program, and inputs solar cell structure information to the design apparatus 100 using the input apparatus 110. When the solar cell structure information is input, the central processing unit 130 stores the solar cell structure information in the solar cell structure information storage unit 172, thereby setting and determining the initial structure of the solar cell to be designed.

  Here, the translucent substrate 1, transparent electrodes (front transparent conductive film 2 and back transparent conductive film 9), a plurality of photoelectric conversion units (first photoelectric conversion unit 11 and second photoelectric conversion unit 12), first connection layer 21, shape information and optical property information about each of the second connection layers 22, a transparent electrode (front transparent conductive film 2 and back transparent conductive film 9), and a plurality of photoelectric conversion units (first photoelectric conversion unit 11 and second photoelectric conversion unit 11). Solar cell structure information (initial structure information) including the photoelectric conversion unit 12), the electrical property information about the first connection layer 21, and the second connection layer 22 is input to the design apparatus 100. The solar cell structure information includes the thickness of each layer in addition to the above information, and the structure of the solar cell is determined.

  For the initial structure, for example, solar cell structure information obtained when optimization is performed under STC conditions may be used. Moreover, solar cell structure information that is optimal in a plurality of spectrum shapes is acquired in advance, and is closest to the spectrum shape that has the highest frequency or the highest accumulated solar radiation intensity at the installation point of the solar cell (solar cell module). In some cases, the solar cell structure information may be used as the initial structure. For example, a certain spectrum shape and solar cell structure information that is optimal for this spectrum shape are prepared in pairs. Then, for example, a pair of design structures that are optimal for the certain spectrum shape that has the spectrum that is the closest to the most frequent spectrum shape at the installation location of the solar cell (solar cell module). The initial structure may be determined as a design structure that is paired with the spectrum. Further, when selecting the optimum design structure for the most frequent spectrum shape, the average photon energy of the spectrum may be selected as a reference. In any case, the solar cell has a structure including the first connection layer 21 and the second connection layer 22.

  Further, the designer inputs environmental information on the installation location of the solar battery cell (solar battery module) including information on solar radiation to the design apparatus 100 using the input device 110. When the environmental information is input, the central processing unit 130 stores the environmental information in the environmental information storage unit 171 so that the environmental information is determined.

  When the initial structure determination process (step S110) is completed, the central processing unit 130, in the optical characteristic calculation process (step S120), external quantum efficiency (EQE: External Quantum Efficiency) corresponding to the given structure information of the solar battery cell. Is calculated for each photoelectric conversion unit using the shape information and the optical property information for all the layers including the light-transmitting substrate 1. EQE is a method using an optical simulator using the above-mentioned shape information and optical property information, and simply calculating light propagation in a solar cell based on the optical properties (refractive index, transmittance) of each layer in the cell structure. It can be calculated by the method of performing. The calculation of EQE is executed by the central processing unit 130 by reading the optical characteristic calculation processing program and using the shape information and optical property information described above.

  As an example, FIG. 4 shows a result of calculating EQE by light propagation calculation. FIG. 4 is a characteristic diagram showing the external quantum efficiency of the solar battery cell obtained by light propagation calculation and the measured external quantum efficiency of the solar battery cell. In FIG. 4, the wavelength [nm] of sunlight is shown on the horizontal axis, and the external quantum efficiency EQE is shown on the vertical axis. FIG. 4 shows that the external quantum efficiency of the solar battery cell obtained by light propagation calculation is in good agreement with the measured external quantum efficiency of the solar battery cell.

  When the optical property calculation process (step S120) is completed, the central processing unit 130 determines the solar radiation intensity information of the installation point of the solar battery cell (solar battery module) at a given time in the solar radiation spectrum calculation process (step S130). The solar radiation spectrum information at a given time on the inclined surface of the solar cell module is calculated. Since the solar cell module is usually installed on an inclined surface such as a roof, the solar spectrum information on the inclined surface of the solar cell module is calculated so as to satisfy the same conditions as the arrangement state. It is best to use an actually measured database for the solar radiation intensity information, but model calculation may be used.

  Actually, since the weather itself fluctuates even on a yearly basis, it takes a great deal of labor to construct a spectrum database under average weather conditions on an actual measurement basis. In Japan, the Japan Meteorological Agency has a database of solar radiation and weather, and the New Energy and Industrial Technology Organization (NEDO) is the organization for the direct and scattered solar radiation on the horizontal plane, and the New Energy and Industrial Technology Development Organization (NEDO). Publishes a database, it is good to model the spectrum using these data.

  For example, by using environmental information such as the latitude / longitude of the installation location of solar cells (solar cell modules) and the time series of the above-mentioned direct / scattered solar radiation, the solar direction, solar altitude, total cloudiness, It is possible to estimate and calculate the sky description parameter consisting of the amount of cloudy surroundings, and to calculate the model when the weather is clear or cloudy. That is, it is possible to perform a model calculation of spectra in various weather conditions. Thereby, a spectrum can be calculated from an existing database, and the cost of creating a spectrum database based on measurement at each point can be reduced. In addition, as detailed environmental information, sky shielding information such as surrounding buildings and horizon at the installation point of the solar cell (solar cell module), light incident on the solar cell due to reflection from the ground and the periphery, and the solar cell Using albedo (reflectivity) defined by the ratio of the amount of direct solar radiation to can improve the accuracy.

  The sky shielding information indicates the ratio of the solid angle at which the blue sky can be seen in the hemispherical surface that is visible when facing the direction perpendicular to the inclined surface of the solar cell module. For example, when the solar module is placed horizontally and there are no obstacles around it, 1.0 is the sky shield information, and when the solar cell module is placed vertically there are no obstacles around. The sky shielding information is 0.5 except for the 1/4 spherical surface corresponding to the lower part of the horizon.

  As an example, FIG. 5 shows a fisheye image of the sky taken on a horizontal plane (equivalent to when the solar cell module is placed vertically). FIG. 5 is an image showing a fisheye image of the sky photographed on a horizontal plane (corresponding to a solar cell module placed vertically) in Amagasaki City, Hyogo Prefecture. In FIG. 5, a black area is an area where a blue sky can be seen, and a white area is an obstacle. The black circle around the outermost part is the horizon. The sky shielding information in this case was 0.9.

  As an example, FIG. 6 shows the solar radiation spectrum intensity in Amagasaki City calculated using the sky description parameter and the sky shielding information. FIG. 6 is a characteristic diagram showing the relationship between the solar radiation spectrum intensity at a certain time in Amagasaki City and the actual solar radiation spectrum intensity calculated using the sky description parameter and the sky shielding information. FIG. 6 shows that the solar radiation spectrum intensity calculated using the sky description parameter and the sky shielding information is in good agreement with the actually measured solar radiation spectrum intensity.

  The calculation of the solar radiation spectrum information is executed by the central processing unit 130 using the solar radiation intensity information stored in the environment information storage means 171 by reading out the electrical characteristic calculation processing program. The solar radiation spectrum information calculation program is included in the electrical characteristic calculation processing program. Moreover, the information on the inclined surface of the solar cell module (information such as the inclination direction and the inclination angle) may be included in the electrical characteristic calculation processing program or may be input from the outside.

  When the solar radiation spectrum calculation step (step S130) is completed, the central processing unit 130 calculates the photocurrents of the first photoelectric conversion unit 11 and the second photoelectric conversion unit 12 in the cell current calculation step (step S140). The photocurrent is calculated using the EQE obtained in the optical characteristic calculation step (step S120) and the solar radiation spectrum information obtained in the solar radiation spectrum calculation step (step S130). The photoelectric current Jph of each photoelectric conversion unit is expressed by the following formula (2) where the solar radiation spectrum at the wavelength λ is Int (λ) and the external quantum efficiency is EQE (λ).

  In equation (2), λ1 is the calculation start wavelength of the photocurrent, and λ2 is the calculation end wavelength of the photocurrent. In many cases, λ1 and λ2 are selected based on the rising wavelength and falling wavelength of EQE. In a solar cell using silicon, in general, λ1 = 300 nm and λ2 = 1200 nm.

  When the cell current calculation step (step S140) is completed, the central processing unit 130, in the cell electric characteristic calculation step (step S150), the electric characteristics of the first photoelectric conversion unit 11 and the second photoelectric conversion unit 12 (short circuit current Jsc, Open circuit voltage Voc, fill factor FF, efficiency η) are calculated. In this process, each electrical characteristic is calculated using the equivalent circuit model of the solar battery cell, the electrical property information calculated based on the structural information of the solar battery cell, and the photocurrent Jph calculated in the cell current calculation process (step S140). Calculate

  In addition to the method of calculating an electric circuit using an equivalent circuit model, there is also a method of simply solving using a database of dark current characteristics Jdk (V) of solar cells, for example. That is, the photocurrent Jph may be added to the dark current characteristic Jdk (V) of the solar battery cell. In addition, it is known that thin film silicon solar cells have a deterioration in electrical characteristics due to light irradiation, so-called light deterioration. For this reason, light degradation generally appears in the dark current characteristics, so it is preferable to include them in the calculation in the cell electrical characteristics calculation step (step S150).

  The calculation of the electrical characteristics of the solar cells is executed by the central processing unit 130 reading out the electrical characteristics calculation processing program and using, for example, the solar radiation intensity information stored in the environment information storage means 171. The equivalent circuit model of the solar battery cell may be included in advance, for example, in the solar battery structure information storage means 172 or the electric characteristic calculation processing program, and based on the given solar battery structure information, the electric characteristic calculation process program It may be calculated or input from the outside.

  When the cell electrical characteristic calculation step (step S150) ends, the central processing unit 130 calculates the cumulative power loss in the cumulative power loss calculation step (step S160). The accumulated power loss is due to the mismatch of the photocurrents of the first photoelectric conversion unit 11 and the second photoelectric conversion unit 12 from the electric characteristics of the respective photoelectric conversion units calculated in the cell electric characteristic calculation step (step S150). The power loss is calculated for a predetermined period at a predetermined time interval and is calculated as a sum. It should be noted that it may be determined as appropriate according to the recording interval of the weather database and the capability of the computer, but it is preferable that the period is one year or more and the interval time is less than one day.

  For the calculation of the accumulated power loss, for example, the unit number em corresponding to each junction of the photoelectric conversion units may be used. Here, the index of the junction of the photoelectric conversion unit is m (for example, from the first photoelectric conversion unit 11 side, top: m = 1, middle: m = 2, bottom: m = 3, etc.) The number (number of pn (pin) junctions) is n. At this time, the unit number em needs to be -em, which is the sum of the unit numbers e other than the index m in all the indices m. As the number of units, for example, as shown in FIGS. 7 and 8, a vector notation or a complex number can be used. Hereinafter, it will be described as a vector notation. FIG. 7 shows the calculation of cumulative power loss due to mismatch of photocurrents between photoelectric conversion units in a two-junction tandem thin-film solar cell in which the number of junctions of the photoelectric conversion units is two (two photoelectric conversion units are stacked). It is a figure which shows vector e1 and vector e2. In this case, vectors 31a (vector e1) and vector 31b (vector e2) having an angle of 180 ° and having the same magnitude are obtained. FIG. 8 shows the calculation of cumulative power loss due to mismatch of photocurrents between photoelectric conversion units in a three-junction tandem thin-film solar cell in which the number of junctions of the photoelectric conversion units is three (three photoelectric conversion units are stacked). It is a figure which shows vector e1-vector e3. In this case, a vector 32a (vector e1), a vector 32b (vector e2), and a vector 32c (vector e3) having an angle of 120 ° and the same magnitude are obtained. Regarding the vector 32a (vector e1), the sum of the vectors em of other m (m = 2, 3) is -e1 (33), which indicates that the above condition is satisfied.

  And, at a given time, calculating the power loss Pm in the junction whose junction index is m for each of the n junctions, and calculating the product of Pm and the vector em for all m , Summing the product of Pm and vector em for all m (calculating the power loss due to photocurrent mismatch of solar cells at a given time), and the given time A cumulative power loss is calculated by performing a step of summing all the power losses due to the mismatch of the photocurrents of the solar cells in a predetermined period.

  Further, when the calculation of the accumulated power loss is expressed in a calculation formula using a complex number, for example, the following formula (3) is obtained. t1 and t2 are calculation start and end times.

In Expression (3), P _{loss_tot} . Is the cumulative power loss in a given period, Pm is the power loss due to photocurrent mismatch at one junction m at a given time, n is the number of photoelectric conversion unit junctions, and m is the photoelectric conversion unit junction index. (For example, from the first photoelectric conversion unit 11 side, top: m = 1, middle: m = 2, bottom: m = 3, etc.). By using the method as described above, it is possible to easily calculate the photocurrent mismatch in each photoelectric conversion unit in the multi-junction thin film solar cell. For example, the calculation of Pm uses the minimum value Jph_min of the photoelectric current Jph of the photoelectric conversion unit and Jph_m which is the photocurrent Jph at the junction of the index m, and the difference in power calculated by each photocurrent Jph (Pm = P (Jph_m) -P (Jph_min) is preferably used as Pm, where P (Jph_m) is the power calculated by Jph_m and P (Jph_min) is the power calculated by Jph_min.

  The calculation of the accumulated power loss is executed by the central processing unit 130 reading out the power loss calculation processing program and using the electrical characteristics of each photoelectric conversion unit calculated in the cell electrical characteristics calculation step (step S150).

  After calculating the power loss at a predetermined time interval, the central processing unit 130 determines whether the calculation of the power loss has been completed for a predetermined period (step S170). Here, when the calculation of the power loss is not completed for the predetermined period (step S170, No), the central processing unit 130 advances the time (step S190) and performs the process from the solar radiation spectrum calculation step (step S130). repeat.

  When the calculation of the power loss has been completed for the predetermined period (step S170, Yes), the central processing unit 130 performs the next optimization determination step (step S180).

In the optimization determination step (step S180), it is determined whether or not the designed solar cell can perform optimal power generation in the environment of the installation location. Here, since the cumulative power loss (P _{loss — tot} .) Calculated in the cumulative power loss calculation step (step S160) becomes 0, the power loss due to the mismatch of the photoelectric currents of the respective photoelectric conversion units becomes a predetermined calculation period. It can be determined that the total is the minimum.

In practice, however, P _{loss — tot} . It is very difficult to set 0 to 0. Therefore, the central processing unit 130 uses P _{loss — tot} . Is compared with a predetermined threshold value that is an optimization criterion of the solar battery cell to determine whether or not the power loss is within an allowable range. The central processing unit 130 uses P _{loss — tot} . Is equal to or less than a predetermined threshold (step S180, Yes), it is determined that the structure of the solar battery cell is optimal, the design structure at this point is determined as the final structure, and the design process is terminated. On the other hand, the central processing unit 130 uses P _{loss — tot} . Is larger than the predetermined threshold value (step S180, No), the structure information adjustment step (step S200) is performed, and the steps after the optical characteristic calculation step (step S120) are repeated. Note that P _{loss — tot} . Is an index for minimizing the mismatch of the photocurrent in a predetermined period, and the power loss due to the mismatch of the photocurrent with respect to the lifetime power generation is actually obtained by integrating Pm over the lifetime of the solar cell.

In the structure information adjustment process (step S200), the central processing unit 130 performs a solar radiation spectrum calculation process (step S130), a cell current calculation process (step S140), a cell electrical characteristic calculation process (step S150), and a cumulative power loss calculation. Based on the information calculated in the process (step S160), the variable part of the structure of the solar cell, that is, the optical property information and the electrical property information, so as to reduce the power loss due to the mismatch of the photocurrent of each photoelectric conversion unit. Then, at least one fine adjustment of the shape information is performed to determine a new design structure. For example, P _{loss — tot} . The balance of the photocurrent Jph between the first photoelectric conversion unit 11 and the second photoelectric conversion unit 12 can be discriminated according to the sign or the position on the complex plane. For this reason, for example, the fine adjustment of the structure may be performed so as to reduce the spectral sensitivity of the photoelectric conversion unit having a large photocurrent Jph or to increase the spectral sensitivity of the photoelectric conversion unit cell having a small photocurrent Jph.

  When it is determined that the necessary performance has been achieved in the optimization determination step (step S180), the operating condition of the solar cell manufacturing apparatus is calculated using the optical physical property information, the electrical physical property information, and the shape information. can do. Based on the calculated operating conditions, a desired solar battery cell can be manufactured by operating a manufacturing apparatus such as a film forming apparatus.

  Table 1 shows the structure optimization adjustment guidelines for the representative spectrum of the material, structure and installation location of each functional layer. In Table 1, BR means Blue Rich, a spectrum with strong intensity on the short wavelength side, and RR means Red Rich, which means a spectrum with strong intensity on the long wavelength side. BR and RR may be determined based on, for example, AM1.5 spectral shape based on whether the intensity at or above a certain wavelength is strong or weak. For example, in a two-junction tandem thin-film solar cell using a photoelectric conversion unit made of amorphous silicon and a photoelectric conversion unit made of microcrystalline silicon, the vicinity of 700 nm, which is the absorption edge of amorphous silicon, is preferably used as the reference wavelength. Further, quantitatively, pseudo air mass approximation or average photon energy may be used. As a representative spectrum, for example, a spectrum having the highest appearance frequency in one year may be taken.

The fine irregularities formed on the surface of the translucent substrate 1 have the light confinement function (b).
The light is bent by a scattering effect due to fine unevenness, and the distance across the first i-type semiconductor film 4 of the first photoelectric conversion unit 11 and the second i-type semiconductor film 7 of the second photoelectric conversion unit 12 is increased (optical path length). Increase action). The principle of scattering due to unevenness changes from Rayleigh scattering to Mie scattering and geometrical optics depending on the size of the unevenness with respect to wavelength. Then, by increasing the size of the irregularities on the surface of the translucent substrate 1, the scattering of light on the long wavelength side increases, and the photocurrent of the second photoelectric conversion unit 12 can be increased.

  Therefore, in the case of the BR spectrum, the unevenness of the surface of the light-transmitting substrate 1 is small (feature size <100 nm), and in the case of the RR spectrum, the unevenness of the surface of the light-transmitting substrate 1 is large (characteristic size> 100 nm). As the feature size, for example, a root mean square roughness Rq, an arithmetic average roughness Ra, an average length RSm of roughness curve elements, and the like may be used. For example, when the feature size is changed from 100 nm to 300 nm, the optical path length increasing action in the second photoelectric conversion unit 12 increases from 1.6 times to 1.8 times.

For the front transparent conductive film 2 as the first electrode layer (transparent electrode layer), zinc oxide (ZnO) or tin oxide (SnO ₂ ) is usually used. SnO ₂ has an absorption edge at a shorter wavelength than ZnO. Therefore, it is preferable to use ZnO in the BR spectrum and SnO ₂ in the RR spectrum for the front transparent conductive film 2. Further, when ZnO is used for the front transparent conductive film 2, the conductivity is improved by doping impurities such as aluminum and boron. However, if the doping amount is large, the transmittance in the infrared region is lowered. Therefore, in the BR spectrum, a low doping amount is particularly preferable.

  As the simplest method for adjusting the EQE of the first photoelectric conversion unit 11 and the second photoelectric conversion unit 12, the ratio of the thicknesses of the first i-type semiconductor film 4 and the second i-type semiconductor film 7 may be changed. By changing the thickness of the i-type semiconductor layer, the ratio of photons absorbed by the first photoelectric conversion unit 11 and the second photoelectric conversion unit 12, that is, the photocurrent Jph can be changed. For example, in the BR spectrum, the first i-type semiconductor film 4 of the first photoelectric conversion unit 11 is thinned to reduce the photocurrent Jph of the first photoelectric conversion unit 11. Conversely, in the RR spectrum, the first photoelectric conversion unit 11 It is preferable to increase the photocurrent Jph of the first photoelectric conversion unit 11 by increasing the thickness of the 1i-type semiconductor film 4. The same applies to the second photoelectric conversion unit 12 in the opposite direction. In the BR spectrum, the thickness of the second i-type semiconductor film 7 is increased to increase the photocurrent Jph of the second photoelectric conversion unit 12, and conversely RR. In the spectrum, it is preferable to reduce the photocurrent Jph of the second photoelectric conversion unit 12 by thinning the second i-type semiconductor film 7.

  Further, as a technique for adjusting EQE, a technique of shifting the absorption edge by changing the band gap of the first i-type semiconductor film 4 of the first photoelectric conversion unit 11 may be used. Since the photocurrent Jph of the first photoelectric conversion unit 11 tends to increase in the BR spectrum, it is preferable to increase the current of the second photoelectric conversion unit 12 by increasing the band gap of the first i-type semiconductor film 4.

  The light absorbed by the first photoelectric conversion unit 11 is limited to the wavelength range from the absorption edge of the first i-type semiconductor film 4 on the long wavelength side to the absorption edge of the front transparent conductive film 2 on the short wavelength side. Therefore, when the band gap of the first i-type semiconductor film 4 of the first photoelectric conversion unit 11 is increased, the absorption edge of the first i-type semiconductor film 4 is shifted to the short wavelength side, and the photocurrent Jph of the first photoelectric conversion unit 11 is decreased. Become. This is suitable for the BR spectrum. For example, the band gap can be increased by increasing the amount of hydrogen in the first i-type semiconductor film 4 of the first photoelectric conversion unit 11 or adding carbon, and the absorption edge of the first i-type semiconductor film 4 can be shortened. It can be shifted to the wavelength side. As a result, the wavelength region absorbed by the first i-type semiconductor film 4 is shortened, and the light transmitted to the second photoelectric conversion unit 12 is increased, so that the current of the second photoelectric conversion unit 12 can be increased.

  Further, as a technique for adjusting EQE, a technique for changing the band gap of the first p-type semiconductor film 3 of the first photoelectric conversion unit 11 may be used. When the band gap of the first photoelectric conversion unit 11 is increased, the absorption of the first p-type semiconductor film 3 is reduced, the light absorbed by the first i-type semiconductor film 4 is increased, and the current of the first photoelectric conversion unit 11 is increased. be able to. This is suitable for RR spectra. The same effect can be obtained even if the band gap of the third connection layer 23 is increased.

Structure dependency between fine irregularities formed on the surface of the translucent substrate 1 and films after the front transparent conductive film 2 (front transparent conductive film 2, first photoelectric conversion unit 11, second photoelectric conversion unit 12) For the first connection layer 21 for relaxing and eliminating the above, it is preferable to use a high refractive index / high transmittance material close to the refractive index of the front transparent conductive film 2. Thereby, the light reflection between the translucent board | substrate 1 and the front transparent conductive film 2 can be suppressed, and the optical dependence of the translucent board | substrate 1 and the front transparent conductive film 2 can be relieve | eliminated and eliminated. When ZnO or SnO ₂ is used for the front transparent conductive film 2, the first connection layer 21 may be formed by a technique such as application of zirconia oxide (ZrO ₂ ), and then the front transparent conductive film 2 may be formed.

  The substrate surface (the surface of the first connection layer 21) after the first connection layer 21 is manufactured is preferably smooth, but may have some unevenness. Note that the connection layer 21 may be omitted if the size of the fine irregularities formed on the surface of the translucent substrate 1 is small to some extent. The allowable unevenness size may be determined according to the requirements of the characteristics of the film after the front transparent conductive film 2.

  The second connection layer 22 for relaxing and eliminating the electrical dependency between the first p-type semiconductor film 3 and the front transparent conductive film 2 of the first photoelectric conversion unit 11 includes a work function of the front transparent conductive film 2, A material having a work function intermediate to the upper end (band end) of the valence band of the first p-type semiconductor film 3 of the first photoelectric conversion unit 11 may be used. For example, titanium oxide may be used for the second connection layer 22. Depending on the energy difference between the work function of the front transparent conductive film 2 and the valence band upper end (band end) of the first p-type semiconductor film 3 of the first photoelectric conversion unit 11, the formation of the second connection layer 22 may be omitted. Good. It is preferable to determine how much energy difference is allowed according to the doping amount of the first p-type semiconductor film 3 and the front transparent conductive film 2 of the first photoelectric conversion unit 11.

It should be noted that which material and structure is finally used is determined by a trade-off with other constraints such as reliability and cost. For example, in general, in a tandem-type thin film silicon solar cell, a photodegradation phenomenon in which power generation efficiency is reduced by irradiating light to an amorphous silicon film used for the first i-type semiconductor film 4 of the first photoelectric conversion unit 11 is known. It has been. Further, it is known that the deterioration rate increases as the first i-type semiconductor film 4 of the first photoelectric conversion unit 11 becomes thicker. Therefore, in order to cope with the photodegradation phenomenon of the first i-type semiconductor film 4, in the case of the RR spectrum, the front transparent conductive film is larger than the thickness of the first i-type semiconductor film 4 of the first photoelectric conversion unit 11. It is effective to use SnO ₂ for ₂ and to reduce the unevenness of the translucent substrate 1.

  In general, the manufacturing cost of the tandem-type thin film silicon solar cell is greatly influenced by the thickness of the microcrystalline silicon film mainly used in the second i-type semiconductor film 7 of the second photoelectric conversion unit 12. Therefore, in the case of the BR spectrum, ZnO is used for the front transparent conductive film 2 rather than making the second i-type semiconductor film 7 of the second photoelectric conversion unit 12 thick, or the unevenness of the translucent substrate 1 is increased, or It is more effective to make the first i-type semiconductor film 4 of the first photoelectric conversion unit 11 thinner.

  As described above, according to the first embodiment, by providing the connection layers (first connection layer 21 and second connection layer 22) in the solar battery cell, the constraint condition due to the dependency between the functional layers is eliminated.・ Suppressed. As a result, each solar cell can be designed independently of the functions and structures of each layer by eliminating and suppressing various dependencies (structure dependency, optical dependency, and electrical dependency). The degree of freedom of design increases, and flexible design according to the environmental conditions of the solar cell (solar cell module) installation location becomes possible.

  In particular, when an anisotropic material such as microcrystalline silicon is used as the functional layer material, the dependence on the base is usually strong, so that a large number of trials are required, making it difficult to deal with various types. However, according to the above embodiment, the optimization of the solar cell structure at the design stage can be easily performed with high accuracy, so that the required number of trial manufactures can be greatly reduced. As a result, the design with the minimum number of prototypes is possible, so that the environmental conditions of the solar cell (solar cell module) installation location can be optimized in a short time, and the manufacturing cost can be reduced. .

  Moreover, the function and structure of each layer of the solar battery cell can be independently designed in a state where the environmental conditions of the installation location are reproduced in the design apparatus 100. Then, the constraint condition for the combination of the film and the substrate having each function is relaxed / resolved, and each functional layer designed independently can be freely combined. As a result, it is possible to easily optimize the structural design based on the computer base with minimal trial production and the environmental conditions of the installation location.

  Therefore, according to the first embodiment, a tandem-type thin film solar cell suitable for the environmental conditions of the installation location can be easily designed and manufactured at low cost.

Embodiment 2. FIG.
The solar cell module rises in temperature when irradiated with sunlight. In the second embodiment, an optimum structure and an optimization design method with respect to a temperature change of the solar cell module at the installation location will be described. FIG. 9 is a flowchart showing the flow of the solar cell design method according to the second embodiment of the present invention. The solar cell design method according to the second embodiment includes an initial structure determination step (step S110), an optical property calculation step (step S120), a solar radiation amount calculation step (step S210), and a junction temperature calculation step (step S220). , A cell current calculation step (step S225), a cell electrical characteristic calculation step (step S230), a cumulative power loss calculation step (step S240), an optimization determination step (step S180), and a structure information adjustment step (step S200).

  Here, a case will be described in which the above-described steps are performed using the structure of the solar battery cell determined to have the optimum structure by implementing the solar battery cell design method according to the first embodiment. Hereinafter, differences from the flowchart of FIG. 2 of the first embodiment will be described. It should be noted that the solar radiation amount calculation step (step S210) to the optimization determination step (step S180) are performed in parallel after the optical characteristic calculation step (step S120) in the flow described in the solar cell design method according to the first embodiment. The structure information adjustment step (step S200) may be performed in common based on the result of the flow optimization determination step (step S180) according to the flow according to the first embodiment and the flow according to the second embodiment. Good.

When the optical property calculation step (step S120) is completed, the central processing unit 130 determines the solar cell (solar cell module) at a given time on the inclined surface of the solar cell module in the solar radiation amount calculation step (step S210). Calculate the amount of solar radiation at the installation point.
In addition, although the solar radiation spectrum calculation process (step S130) in Embodiment 1 may be used, since spectrum distribution is not considered, Embodiment 2 demonstrates the case where the solar radiation amount is used as integral intensity. The solar radiation amount is calculated from the solar radiation intensity information. It is best to use an actually measured database for the solar radiation intensity information, but model calculation may be used.

  When the solar radiation amount calculating step (step S210) is completed, the central processing unit 130 determines the junction temperature, that is, the first i-type semiconductor film 4 and the second of the first photoelectric conversion unit 11 in the junction temperature calculating step (step S220). The temperature of the second i-type semiconductor film 7 of the photoelectric conversion unit 12 is calculated. Note that the thickness of the p-type semiconductor film and the n-type semiconductor film is very thin compared to the thickness of the i-type semiconductor film. For this reason, the temperature of the i-type semiconductor film is adopted here as the temperature of the junction between the p-type semiconductor film and the n-type semiconductor film and the i-type semiconductor film. The temperature of the first i-type semiconductor film 4 and the second i-type semiconductor film 7 can be determined by a method using a nominal operating cell temperature (NOCT), a solar radiation amount (solar radiation intensity information), an outside, based on the solar radiation intensity information. The junction temperature may be obtained by a method of calculating heat transfer from the air temperature, wind speed, installation state, and the like.

  For example, in addition to the amount of solar radiation, create a database of the heat transfer coefficient between the solar cell module and the outside air using the four variables of installation angle, installation direction, wind direction, and wind speed of the solar cell module, and use this information Therefore, it is possible to predict the junction temperature with high accuracy. There is a method using simulation for obtaining the heat transfer coefficient. In actual measurement, there are a method for obtaining energy from light irradiation, current injection, etc., and obtaining from a steady reaching temperature, a method for obtaining from a transient temperature drop, a temperature rise curve, and the like.

  When the junction temperature calculation step (step S220) is completed, the central processing unit 130 calculates a photocurrent reflecting the junction temperature of each photoelectric conversion unit in the cell current calculation step (step S225). In the cell current calculation step (step S140), the photocurrent is calculated by using the solar radiation amount obtained in the solar radiation amount calculation step (step S210) instead of the solar radiation spectrum information, and the cell current calculation step (step S140). Similarly, it is calculated using equation (2). When the cell current calculation step (step S225) is completed, the central processing unit 130 determines the electrical characteristics (short circuit current Jsc, open circuit voltage Voc, fill factor FF, efficiency η) of the solar cell in the cell electrical property calculation step (step S230). ). In this process, the solar radiation amount calculated in the solar radiation amount calculating step (step S210) and the cell current calculating step (step S225) using the given structure information of the solar battery cell and the equivalent circuit model of the solar battery cell. ) And the temperature of the first i-type semiconductor film 4 of the first photoelectric conversion unit 11 and the second i-type semiconductor film 7 of the second photoelectric conversion unit 12 calculated in the junction temperature calculation step (Step S220). The parameters in the equivalent circuit model are adjusted based on the above, and each electrical characteristic is calculated. That is, each electrical characteristic is calculated based on the photocurrent reflecting the junction temperature of each photoelectric conversion unit.

  In addition to the method of calculating an electric circuit using an equivalent circuit model, there is also a method of simply solving using, for example, a database of dark current characteristics Jdk (V) of solar cells and the temperature dependence of each characteristic. In this case, the dark current characteristic at the target temperature to be calculated is calculated by multiplying the dark current characteristic Jdk (V) of the solar battery cell by a correction coefficient corresponding to the temperature, and the photocurrent Jph is added thereto to obtain the characteristic. It is good to ask.

  When the cell electrical characteristic calculation process (step S230) is completed, the central processing unit 130 determines the junction temperature, that is, the first i-type semiconductor film 4 and the first photoelectric conversion unit 11 of the first photoelectric conversion unit 11 in the cumulative power loss calculation process (step S240). The cumulative power loss due to the temperature of the second i-type semiconductor film 7 of the two photoelectric conversion unit 12 is calculated. The cumulative power loss is calculated by calculating the power loss in the solar battery cell due to the junction temperature and calculating the power loss at a predetermined time for a predetermined period. The power loss is the junction temperature calculated in the above junction temperature calculation step (step S220), that is, the first i-type semiconductor film 4 of the first photoelectric conversion unit 11 and the second i-type semiconductor film of the second photoelectric conversion unit 12. It is good to define with the difference of the electric power generated in the photovoltaic cell when the temperature of 7 is not considered, and the electric power generated of the photovoltaic cell when considering the junction temperature.

  After calculating the power loss at a predetermined time interval, the central processing unit 130 determines whether the calculation of the power loss has been completed for a predetermined period (step S170). Here, when the calculation of the power loss is not completed for the predetermined period (step S170, No), the central processing unit 130 advances the time (step S190) and performs the processing from the solar radiation amount calculation step (step S210). repeat.

  When the calculation of the power loss has been completed for the predetermined period (step S170, Yes), the central processing unit 130 performs the next optimization determination step (step S180).

  In the optimization determination step (step S180), it is determined whether or not the designed solar cell can perform optimal power generation in the environment of the installation location. Here, the accumulated power loss calculated in the accumulated power loss calculation step (step S240) becomes 0, so that the power loss in the solar battery cells due to the junction temperature is minimized in a predetermined calculation period. It can be judged.

  However, in practice, it is very difficult to set the accumulated power loss to zero. For this reason, the central processing unit 130 compares the accumulated power loss with a predetermined threshold value, and determines that the structure of the solar battery cell is optimal when the accumulated power loss is equal to or less than the predetermined threshold value (step S180, Yes). Then, the design structure at this point is determined as the final structure, and the design process is terminated. On the other hand, when the accumulated power loss is larger than the predetermined threshold (No at Step S180), the central processing unit 130 performs the structure information adjustment process (Step S200). This cumulative power loss is only an index when minimizing the power loss due to the junction temperature in a predetermined period. Actually, the power loss due to the junction temperature relative to the lifetime power generation amount is calculated based on the power loss for a predetermined service life. It is the total of the period.

  Next, the optimization guideline of the solar cell structure with respect to the temperature change of the installation location will be described. The temperature characteristics of the solar cell are mainly affected by a decrease in the open-circuit voltage Voc, so that adjustment of the band gap of the semiconductor film is effective. Usually, amorphous silicon is used for the first i-type semiconductor film 4 of the first photoelectric conversion unit 11. The variation coefficient of the open-circuit voltage of the first photoelectric conversion unit 11 from the band gap is approximately 0.25% / ° C. Usually, microcrystalline silicon is used for the second i-type semiconductor film 7 of the second photoelectric conversion unit 12. The variation coefficient of the open-circuit voltage of the second photoelectric conversion unit 12 from the band gap is approximately 0.5% / ° C. Since the first photoelectric conversion unit 11 and the second photoelectric conversion unit 12 are electrically connected in series, they are actually the sum of these. However, since the open circuit voltages of the respective photoelectric conversion units are different, the coefficient of variation is a weighted sum thereof, which is about 0.3% / ° C.

In order to adjust the temperature characteristic of the open circuit voltage Voc of the solar battery cell, the doped layer (first p-type semiconductor film 3, second p-type semiconductor film 6, first n-type) of the first photoelectric conversion unit 11 or the second photoelectric conversion unit 12 is used. The band gap and thickness of the semiconductor film 5 and the second n-type semiconductor film 8) are adjusted.
When the band gap of the doped layer is increased, the minority carrier density is decreased, so that the coefficient of variation is decreased. In order to increase the band gap of the doped layer, for example, carbon or oxygen may be added. Such adjustment is particularly effective for the RR spectrum. Further, when the thickness of the doped layer is reduced, the amount of minority carriers is reduced, so that the coefficient of variation is reduced.

  The third connection layer 23 for relaxing and eliminating the electrical dependency between the first p-type semiconductor film 3 and the first i-type semiconductor film 4 of the first photoelectric conversion unit 11 includes the first p of the first photoelectric conversion unit 11. It is preferable to use a material in which the upper end of the valence band is located at an intermediate position between the upper end (band end) of the valence band of the type semiconductor film 3 and the first i-type semiconductor film 4. By configuring the third connection layer 23 with such a material, the electrical dependency between the first p-type semiconductor film 3 and the first i-type semiconductor film 4 can be relaxed, and the characteristics and structure of the first p-type semiconductor film 3 can be improved. Can be designed independently.

  For example, when amorphous silicon carbide (a-SiC) is used for the first p-type semiconductor film 3 of the first photoelectric conversion unit 11, an amorphous silicon carbide (a-SiC) film with a reduced amount of carbon is used. It is good to make. In order to provide the same function as that of the third connection layer 23, a similar configuration is appropriately formed between the first i-type semiconductor film 4 and the first n-type semiconductor film 5 of the first photoelectric conversion unit 11. In addition, the second photoelectric conversion unit 12 may have the same configuration. Thereby, the characteristic and structure of each layer of the 1st photoelectric conversion unit 11 and the 2nd photoelectric conversion unit 12 can be designed independently.

  In addition, when the 3rd connection layer 23 is required by adjusting the band gap of the dope layer of the 1st photoelectric conversion unit 11 and the 2nd photoelectric conversion unit 12, the 3rd connection layer 23 absorbs light, and electric power generation efficiency May decrease. Therefore, it is necessary to determine which structure is optimal according to the temperature change of the installation location.

  As an example of the design, an example in which the thickness of the first i-type semiconductor film 4 of the first photoelectric conversion unit 11 is optimized as a solar cell (solar cell module) installed in Miyakojima is shown. In Miyakojima, the amount of solar radiation in the BR spectrum is larger than the STC condition mainly because of the latitude. Moreover, since Miyakojima is located in the south, the junction temperature tends to be high. Therefore, by combining the first embodiment and the second embodiment, the thickness of the first i-type semiconductor film 4 of the first photoelectric conversion unit 11 which is 240 nm in the STC condition is 160 nm, and the structure of the solar battery cell is By optimizing, the annual power generation increased by 8%.

  In the first embodiment, the optimization for the incident spectrum of the installation place of the solar battery cell (solar battery module) was performed, and in the second embodiment, the optimization for the temperature of the installation place of the solar battery cell (solar battery module) was performed. In practice, it is preferable to design the final optimum structure by combining these in a matrix.

  For example, a map of cumulative solar radiation is created using the solar cell module temperature and spectral features (average photon energy, etc.). In addition to the solar cell module temperature and spectrum, it is optimal for the effects of incident angle and shadows. There is also a change axis, so the number of combinations becomes enormous. Considering the optimization of the solar cell (solar cell module) installation location to the environmental conditions, in this background, it is necessary to verify the dependence and characteristics for each combination by trial production in the conventional method. Is very difficult.

  On the other hand, in the first embodiment and the second embodiment, by providing the connection layers (the first connection layer 21, the second connection layer 22, and the third connection layer 23), restrictions caused by the dependency between the functional layers. Conditions are eliminated / suppressed. As a result, each solar cell can be designed independently of the functions and structures of each layer by eliminating and suppressing various dependencies (structure dependency, optical dependency, and electrical dependency). The degree of freedom of design increases, and flexible design according to the environmental conditions of the solar cell (solar cell module) installation location becomes possible.

  In particular, when an anisotropic material such as microcrystalline silicon is used as the functional layer material, the dependence on the base is usually strong, so that a large number of trials are required, making it difficult to deal with various types. However, according to the above embodiment, the optimization of the solar cell structure at the design stage can be easily performed with high accuracy, so that the required number of trial manufactures can be greatly reduced. As a result, the design with the minimum number of prototypes is possible, so that the environmental conditions of the solar cell (solar cell module) installation location can be optimized in a short time, and the manufacturing cost can be reduced. .

  Moreover, the function and structure of each layer of the solar battery cell can be independently designed in a state where the environmental conditions of the installation location are reproduced in the design apparatus 100. The functional layers designed in this way can be freely combined. As a result, it is possible to easily optimize the structural design based on the computer base with minimal trial production and the environmental conditions of the installation location.

  Therefore, according to the second embodiment, a tandem-type thin film solar cell suitable for the environmental conditions of the installation location can be easily designed and manufactured at low cost.

Embodiment 3 FIG.
In the first and second embodiments, in the cell current calculation step (step S140) and the cell current calculation step (step S225), the photocurrent Jph of each photoelectric conversion unit is absorbed by the photoelectric conversion unit using equation (2). Calculations were made assuming that the number of photons is proportional. However, strictly speaking, the photocurrent and the number of photons are not proportional to each other due to loss inside the photoelectric conversion unit. In particular, when the number of incident photons is small, and generally when the amount of solar radiation incident on the photoelectric conversion unit is small, Jph is smaller than the result obtained by Expression (2). In the third embodiment, correction means for the deviation from the proportional relationship between the number of photons and the photocurrent Jph will be described.

  FIG. 10 is a flowchart showing the cell current calculation step (step S300) according to the third embodiment. In the actual design flow, the cell current calculation step (step S140) in the first embodiment, the cell current calculation step (step S225) in the second embodiment, and the cell current calculation step in the third embodiment. (Step S300). Therefore, since the other flow of design is the same as Embodiment 1 or Embodiment 2, description is abbreviate | omitted here. The cell current calculation step (step S300) in the third embodiment includes the absorption photon number calculation step (step S310), the internal loss calculation step (step S320), the photocurrent calculation step (step S330), and the cell current calculation end determination step ( Step S340).

  When the solar radiation spectrum calculation step (step S130) is completed in the previous flow, that is, the flow of the first embodiment, and the junction temperature calculation step (step S220) is completed in the flow of the second embodiment, the central processing unit 130 calculates the cell current. A process (step S300) is started. That is, the central processing unit 130 first calculates the number of photons absorbed in each photoelectric conversion unit in the absorption photon number calculation step (step S310). In the flow of the first embodiment, the number of absorbed photons includes the external quantum efficiency EQE obtained in the optical characteristic calculation step (step S120) and the solar radiation spectrum information obtained in the solar radiation spectrum calculation step (step S130). And is calculated by the following equation (4).

In Expression (4), nph (λ) is the number of photons absorbed by the photoelectric conversion unit at the wavelength λ, and q is an elementary charge (1.6 × 10 ⁻¹⁹ C). Moreover, in the flow of Embodiment 2, it calculates by Formula (4) using the solar radiation amount obtained at the solar radiation amount calculation process (step S210) instead of solar radiation spectrum information. In the case where the junction temperature information is calculated in the junction temperature part calculation step (step S220), the junction temperature information may be reflected in the external quantum efficiency EQE.

  When the absorption photon number calculation step (step S310) is completed, the central processing unit 130 calculates the internal loss when converting the photons absorbed by each photoelectric conversion unit into a photocurrent in the internal loss calculation step (step S320). . As a method for calculating the internal loss, for example, there is a method of calculating the approximation by reducing the loss as a constant term R independent of nph (λ). Further, the distribution of photogenerated carriers in the depth direction in the first i-type semiconductor film 4 and the second i-type semiconductor film 7 is calculated from nph (λ), and carrier generation by light irradiation → drift in the i-type semiconductor film → electrode There is a technique for calculating internal loss by calculating loss processes such as recombination loss in the i-type semiconductor film during drift and recombination loss at the interface in the carrier collection process, which is a process of collecting the. In this case, the loss term R is not a constant but a function depending on the wavelength (λ) and nph (λ).

  When the internal loss calculation step (step S320) is completed, the central processing unit 130 calculates the photocurrent in each photoelectric conversion unit in the photocurrent calculation step (step S330). The photocurrent may be calculated by applying a correction term to nph (λ) according to the technique used in the internal loss calculation step (step S320). For example, when the internal loss is approximated as a constant term independent of nph (λ), the photocurrent is calculated by the following equation (5).

  In equation (5), λ1 is the calculation start wavelength of the photocurrent, and λ2 is the calculation end wavelength of the photocurrent. In many cases, λ1 and λ2 are selected based on the rising wavelength and falling wavelength of EQE. In a solar cell using silicon, in general, λ1 = 300 nm and λ2 = 1200 nm. In equation (5), the photocurrent can be calculated by multiplying the result obtained by subtracting the internal loss R from the value obtained by integrating nph (λ) in the specified wavelength range by the elementary charge. FIG. 11 shows the dependence of the actually measured photocurrent Jph on the amount of solar radiation and the dependence of the photocurrent on the amount of solar radiation calculated from the model of equation (5) using internal loss. In FIG. 11, the normalized solar radiation rate (%) is shown on the horizontal axis, and the normalized cell current rate (%) is shown on the vertical axis. The normalized solar radiation rate is a ratio of the solar radiation amount when a certain solar radiation amount is used as a reference (100%). The normalized cell current ratio is the ratio of the cell current when the cell current in the case of the standard (100%) solar radiation amount is used as the reference (100%). The vertical axis indicates the deviation from the proportional relationship when the normalized cell current ratio is 100% and is in a proportional relationship.

  When the photocurrent calculation step (step S330) is completed, the central processing unit 130 determines whether the cell current has been calculated in all the photoelectric conversion units in the cell current calculation end determination step (step S340). When the calculation of the cell current is not completed in all the photoelectric conversion units (No at Step S340), the calculation is performed from the absorption photon number calculation step (Step S310) for the next photoelectric conversion unit. When the calculation has been completed for all the photoelectric conversion units (step S340, Yes), the process proceeds to the next step.

The optimization guideline for the solar cell structure in the third embodiment is basically the same as that in the first and second embodiments. FIG. 12 to FIG. 14 show the ratio (contribution rate) that the period of each solar radiation amount contributes to the total solar radiation energy for one year observed in various parts of the world. This contribution rate represents the percentage of the total solar radiation energy in one year, that is, the energy poured by the solar radiation amount of each solar radiation amount section. FIG. 12 is a histogram showing the ratio of each solar radiation amount period to the total solar radiation energy for one year in the temperate region. FIG. 13 is a histogram showing the ratio of the period of each solar radiation amount to the total solar radiation energy for one year in the tropical region. FIG. 14 is a histogram showing the contribution ratio of each solar radiation amount to the total solar radiation energy for one year in the desert region. In FIG. 12 to FIG. 14, the solar radiation amount [W / m ² ] is shown on the horizontal axis, and the ratio (contribution rate) that the period of each solar radiation amount contributes to the total solar radiation energy for one year is shown on the vertical axis.

  From these figures, in all of the temperate zone (Fig. 12), the tropical zone (Fig. 13), and the desert zone (Fig. 14), that is, regardless of the climate, the period of low solar radiation is one year. It can be seen that it contributes to energy. On the other hand, the main cause of the decrease in solar radiation differs between the temperate region and the tropical and desert regions in terms of climate. In temperate areas, cloudy weather is the main cause of reduced solar radiation. In tropical and desert areas, lower solar altitude is the main cause of reduced solar radiation.

  Therefore, the influence of the solar radiation amount on the spectrum when the solar radiation amount is small is stronger in the tropical region and the desert region, and the spectrum changes greatly in the tropical region and the desert region due to the influence of atmospheric scattering (such as sunset). On the other hand, in the temperate region, the spectrum does not change greatly even if the amount of solar radiation is small. Therefore, the third embodiment is preferably used for optimization in the case of installation in a sunny climate such as a tropical region and a desert region.

  As described above, in the third embodiment, current loss due to internal loss when converting photons absorbed by the photoelectric conversion unit into photocurrent is considered. Further, the correction of the current loss due to the internal loss can be performed by subtracting the constant value from the current value obtained from the proportional relationship with the solar radiation spectrum information. According to the third embodiment, even when the change in spectrum due to a decrease in the amount of solar radiation is large and the number of photons absorbed by the photoelectric conversion unit and the photocurrent Jph are not in a proportional relationship, It is possible to easily design a tandem-type thin film solar cell suitable for the environmental conditions of the installation site and to manufacture it at a low cost by correcting the deviation.

  As described above, the method for designing a tandem thin-film solar battery according to the present invention is useful for easily and inexpensively manufacturing a tandem thin-film solar battery suitable for the environmental conditions of the installation site.

  DESCRIPTION OF SYMBOLS 1 Translucent board | substrate, 2 Front transparent conductive film, 3 1st p-type semiconductor film, 4 1st i-type semiconductor film, 5 1st n-type semiconductor film, 6 2nd p-type semiconductor film, 7 2nd i-type semiconductor film, 8 2nd n Type semiconductor film, 9 back transparent conductive film, 10 back reflector, 11 first photoelectric conversion unit, 12 second photoelectric conversion unit, 21 first connection layer, 22 second connection layer, 23 third connection layer, 31a vector e1, 31b vector e2, 32a vector (e1), 32b vector (e2), 32c vector (e3), 100 design device, 110 input device, 111 user input device, 112 external storage medium input device, 120 display device, 130 central processing unit , 140 storage device, 141 main storage device, 142 secondary storage device, 150 output means, 160 bus line, 161 Optical characteristic calculation processing program, 162 Electrical characteristic calculation processing program, 163 Power loss calculation processing program, 164 Optimal determination processing program, 165 Structure information adjustment processing program, 166 Output processing program, 171 Environmental information storage means, 172 Solar cell structure information storage Means, em, e1, e2, e3 vectors.

Claims (21)

A transparent electrode layer and a plurality of photoelectric conversion units made of a plurality of semiconductor films with different impurity doping conditions are laminated in this order on a light-transmitting substrate, and a connection layer that eliminates the characteristic dependency between each layer A first connection layer that is provided between the translucent substrate and the transparent electrode layer and eliminates the shape dependence of the translucent substrate; and on the transparent electrode layer side of the plurality of photoelectric conversion units The impurity doping condition is different from the second connection layer provided between the first photoelectric conversion unit and the transparent electrode layer to eliminate the electrical dependency between the first photoelectric conversion unit and the transparent electrode layer. A third connection layer provided between the semiconductor films to eliminate electrical dependence between the semiconductor films, and a method for designing a tandem thin film solar cell in which sunlight is incident from the translucent substrate side There,
A first step of determining environmental information of an installation location of the tandem-type thin film solar cell including information on solar radiation;
Shape information and optical property information about the translucent substrate, the transparent electrode layer, the plurality of photoelectric conversion units, and the connection layer, and an electrical property about the transparent electrode layer, the plurality of photoelectric conversion units, and the connection layer A second step of determining a design structure of the tandem-type thin film solar cell to be designed based on the information;
A third step of calculating optical property information for each photoelectric conversion unit with respect to sunlight incident from the translucent substrate side using the optical property information and the shape information;
A fourth step of calculating the electrical property information of the design structure using the electrical property information, the optical property information, and the information on the solar radiation;
A fifth step of calculating a power loss of the design structure using the electrical characteristic information;
A sixth step of determining whether the power loss is within an allowable range by comparing the power loss with a predetermined threshold;
Including
In the sixth step, when the power loss is equal to or less than the predetermined threshold, the design is finished with the design structure as a final structure,
In the sixth step, when the power loss is larger than the predetermined threshold value, a new design structure is determined by adjusting at least one of the optical property information, the electrical property information, and the shape information. Repeatedly performing the third and subsequent steps after performing the seventh step;
A method for designing a tandem-type thin film solar cell. In the fourth step, each photocurrent in the plurality of photoelectric conversion units is calculated, and the electrical characteristic information is calculated based on the photocurrent,
In the fifth step, calculating a power loss due to mismatch of photocurrents in the plurality of photoelectric conversion units,
The method for designing a tandem-type thin film solar cell according to claim 1. The environmental information includes latitude and longitude information of the installation location and sky shielding information,
The fourth step includes
Calculating solar radiation spectrum information at the installation location using the environmental information and information on the solar radiation;
Using the solar radiation spectrum information and optical characteristic information for each photoelectric conversion unit, calculating a photocurrent for each photoelectric conversion unit;
Calculating electrical property information of the design structure using a photocurrent for each photoelectric conversion unit;
The method for designing a tandem-type thin film solar cell according to claim 2, comprising: The step of calculating the photoelectric current for each photoelectric conversion unit is to correct the loss due to internal loss from the current value obtained from the proportional relationship to the solar radiation spectrum information,
The method for designing a tandem-type thin film solar cell according to claim 2 or 3. The correction of the loss due to the internal loss is obtained by subtracting a constant value from the current value obtained from the proportional relationship to the solar radiation spectrum information.
The design method of the tandem-type thin film solar cell according to claim 4. The step of calculating the solar radiation spectrum information includes:
Calculating a sky description parameter composed of solar altitude, solar orientation, and cloudiness using the environmental information, and calculating the solar radiation spectrum information including the sky description parameter;
The method for designing a tandem-type thin film solar cell according to any one of claims 3 to 5. Calculating the power loss due to the mismatch of the photocurrents,
The number of junctions of the photoelectric conversion unit is n (2 ≦ n),
Unit number em corresponding to each junction of the photoelectric conversion units em (m is an index of junction), and a unit that becomes -em when all unit numbers e other than any one unit number em are added Using the number e
calculating the power loss Pm of each of the m junctions;
Calculating the product of Pm and the number of units em for all m;
Adding the product of the Pm and the number of units em to all m and calculating the power loss due to photocurrent mismatch at a certain time;
Including
In the sixth step,
Calculate the cumulative power loss by integrating the power loss due to photocurrent mismatch at a certain time for a predetermined period,
Terminating the design with the design structure as a final structure when the accumulated power loss is less than or equal to the predetermined threshold;
The method for designing a tandem-type thin film solar cell according to any one of claims 2 to 6. The step of calculating the power loss due to the mismatch of the photocurrents calculates the cumulative power loss using the following formula (1) using a complex number as a unit number,
Terminating the design with the design structure as a final structure when the cumulative power loss over a predetermined period is less than or equal to the predetermined threshold;
The method for designing a tandem-type thin film solar cell according to any one of claims 2 to 6.
The tandem-type thin film solar cell includes a third connection layer that is provided between semiconductor films having different impurity doping conditions and eliminates electrical dependence between the semiconductor films,
After the first step,
An eighth step of calculating the amount of solar radiation information at the installation location using the information about the solar radiation;
A ninth step of calculating the temperature of the junction between the semiconductor films in the photoelectric conversion unit based on the solar radiation amount information;
A tenth step of calculating the electrical property information of the design structure independently from the electrical dependence between the semiconductor films using the solar radiation information and the temperature of the junction;
An eleventh step of calculating a power loss of the design structure due to the temperature of the junction using the electrical characteristic information;
Is further implemented,
In the eleventh step, when the power loss due to the temperature of the junction is equal to or less than the predetermined threshold, the design structure is determined as the final structure, and the design is finished.
In the eleventh step, if the power loss due to the temperature of the junction is larger than the predetermined threshold value, the optical property information, the electrical property information, and the shape information are adjusted to adjust the power loss. Repeatedly performing the eighth and subsequent steps after performing the twelfth step of determining a proper design structure,
The method for designing a tandem-type thin film solar cell according to any one of claims 1 to 8. In the step of calculating the temperature of the joint,
The heat transfer coefficient between the tandem thin film solar cell and the outside air is calculated using information on the installation inclination angle, the installation direction, the wind direction, and the wind speed of the tandem thin film solar cell at the installation location in the environmental information. Process,
Calculating the temperature of the joint using the solar radiation information and the heat transfer rate;
The method for designing a tandem-type thin film solar cell according to claim 9. In the second step, the design structure is determined using structure information of the tandem-type thin film solar cell suitable for STC conditions as the initial structure information.
The method for designing a tandem thin film solar cell according to claim 1, wherein: In the second step, a plurality of pairs of design structures that are optimal for a certain spectrum shape are provided in advance, and a spectrum that is closest to the most frequently used spectrum shape at the installation location is provided in advance. Selecting from among a pair of design structures that are optimal for the certain spectral shape, and determining an initial structure as a design structure that is paired with the spectrum;
The method for designing a tandem-type thin film solar cell according to any one of claims 1 to 11. When selecting the design structure that is optimal for the most frequent spectral shape, selecting on the basis of the average photon energy of the spectrum;
The method for designing a tandem-type thin film solar cell according to claim 12. Causing a computer to execute the method for designing a tandem-type thin film solar cell according to any one of claims 1 to 13,
Design program characterized by Executing a process of outputting the solar cell structure determined as the final structure to output means connected to the computer;
The design program according to claim 14. On the translucent substrate, a transparent electrode layer and a plurality of photoelectric conversion units made of a plurality of semiconductor films having different impurity doping conditions are laminated in this order,
As a connection layer that relaxes the characteristic dependency between adjacent layers,
A first connection layer provided between the translucent substrate and the transparent electrode layer to eliminate the shape dependency due to the translucent substrate;
The electrical dependency between the first photoelectric conversion unit and the transparent electrode layer is eliminated by being provided between the first photoelectric conversion unit on the transparent electrode layer side and the transparent electrode layer among the plurality of photoelectric conversion units. A second connection layer,
A third connection layer that is provided between the semiconductor films having different doping conditions of the impurities and eliminates electrical dependence between the semiconductor films;
With
Each of the connection layers is
For at least one characteristic of interface shape, refractive index, band edge energy,
Having a characteristic between the value of the structure immediately below the connection layer and the value of the structure immediately above the connection layer;
A tandem-type thin film solar cell. The surface roughness of the interface between the first connection layer and the transparent electrode layer is the surface roughness of the interface between the first connection layer and the translucent substrate, and between the first connection layer and the first connection layer. A value between the surface roughness of the interface with the layer immediately above,
The tandem-type thin film solar cell according to claim 16. Concavities and convexities are formed on the surface of the transparent electrode layer in the transparent substrate made of glass,
The transparent electrode layer made of zinc oxide or tin oxide is formed on the unevenness of the translucent substrate via the first connection layer containing zirconium oxide;
The tandem-type thin film solar cell according to claim 17. Each of the plurality of photoelectric conversion units is formed by laminating a p-type semiconductor film, an i-type semiconductor film, and an n-type semiconductor film in this order from the translucent substrate side,
The second connection layer is provided between the transparent electrode layer and the first photoelectric conversion unit on the transparent electrode layer side among the plurality of photoelectric conversion units,
The second connection layer has a work function between a work function of the transparent electrode layer and a valence band upper end of the p-type semiconductor film of the first photoelectric conversion unit;
The tandem-type thin film solar cell according to any one of claims 16 to 18. The transparent electrode layer is made of zinc oxide or tin oxide;
The p-type semiconductor film of the first photoelectric conversion unit is made of amorphous silicon;
The second connection layer is made of a material containing titanium oxide;
The tandem-type thin film solar cell according to claim 19. The third connection layer is made of a material in which the upper end of the valence band comes to an intermediate position between the upper end of the valence band of the semiconductor film immediately below the third connection layer and the semiconductor film immediately above the third connection layer. about,
The tandem-type thin film solar cell according to any one of claims 16 to 20.