KR20220165016A - Solar power generation system - Google Patents

Abstract

According to one aspect of the present invention, a solar power generation system is provided. The solar power generation system is made of a plurality of solar panels. The plurality of solar panels are formed on at least a part of an outer wall area of a building. Surface roughness of the plurality of solar panels may be different depending on a location where they are attached to the building.

Description

Solar power generation system

The present invention relates to a photovoltaic power generation system, and more particularly, to a building-integrated photovoltaic (BIPV) system. Photovoltaic power generation having a double-sided light-receiving solar cell module having improved transmittance using a silver oxide transparent electrode so as to be applicable to a building-integrated photovoltaic (BIPV) system. It's about the system.

In order to respond to the climate crisis and environmental pollution caused by the use of fossil fuels, the importance of renewable energy sources such as solar power, wind power, wave power, and hydrogen energy is increasing. Recently, research on generating electricity directly from buildings in cities by applying solar cells to BIPV (Building-Integrated Photovoltaic) systems is in progress. Transparent BIPV windows can be installed on most exterior walls of buildings and generate power while transmitting visible light from the outside of the building to the inside of the building.

In the case of BIPV windows, various thin-film solar cells such as organic solar cells (OPV), dye-sensitized solar cells, amorphous silicon, and perovskite solar cells are being studied. Considering the long lifetime of buildings, the stability of organic solar cells, dye-sensitized or perovskite solar cells have not yet been validated for BIPV applications. In contrast, hydrogenated amorphous silicon (a-Si:H) thin-film solar cells have various advantages over BIPV windows. It is cheaper, non-toxic, and has higher manufacturability for large-area substrates. In addition, the stability of the hydrogenated amorphous silicon thin film solar cell was demonstrated in the field, and the hydrogenated amorphous silicon thin film solar cell with various colors or transmittances meeting the actual requirements of the building was demonstrated.

In general, the solar cell measures the luminous intensity based on 100 mW/cm 2 of light perpendicularly incident on the solar cell (1 sun). However, in most practical applications, light does not enter the BIPV system vertically. Therefore, BIPV devices have no choice but to operate in low light conditions. In order to increase generated power, most solar cell devices improve efficiency by using a light trapping structure. The light trapping structure increases the path length for light absorption to generate more light-generated current. In the case of a hydrogenated amorphous silicon thin film solar cell, the light trap structure can be implemented by texturing the front electrode of the cell to effectively scatter incident light to improve the output current.

However, the light trapping structure generally has a morphological complexity capable of scattering incident light, but hinders the growth of a uniform and perfect active layer. Therefore, the light trapping structure may cause a defect in which the output current is unintentionally reduced due to the recombination of the carriers of the solar cell.

In addition, current loss increases according to the intensity of incident light and the behavior of the thin film solar cell for the light trapping effect is complicated. Therefore, it is difficult to evaluate light trapping structures independent of light intensity for the performance of solar cells. In BIPV applications, the intensity of sunlight depends on the actual conditions of the external environment, such as geographic location, installation angle, sun position and weather conditions. Therefore, in order to predict the characteristics of BIPV devices, it is important to understand the light trapping effect of thin-film solar cell devices under various illumination conditions, and an optimal photovoltaic power generation system considering various conditions must be developed.

Solar cell modules applied to conventional BIPV systems have to overcome problems related to poor reliability during long-term operation, and there is a problem that requires the development of a new type of electrode with high transparency and excellent conductivity. Another object of the present invention is to provide an optimal photovoltaic power generation system in consideration of different photovoltaic power generation efficiencies depending on the intensity of illumination. However, these tasks are illustrative, and the scope of the present invention is not limited thereby.

According to one aspect of the present invention for solving the above problems, a photovoltaic power generation system is provided.

The photovoltaic power generation system is a photovoltaic power generation system composed of a plurality of photovoltaic panels, wherein the plurality of photovoltaic panels are formed on at least a portion of an outer wall area of a building, and the surface roughness of the plurality of photovoltaic panels is attached to the building. Each may be different depending on the location to be.

In the photovoltaic power generation system, surface roughness of the plurality of photovoltaic panels may increase relatively from an edge of an outer wall of the building to a central portion.

In the photovoltaic power generation system, surface roughness of the plurality of solar panels may be relatively increased from one edge portion of the outer wall of the building to the other edge portion.

In the photovoltaic power generation system, surface roughness of the plurality of photovoltaic panels may increase relatively from a lower layer to an upper layer of an outer wall of the building.

In the photovoltaic power generation system, the plurality of photovoltaic panels according to a difference in surface roughness of the solar panels attached to an area where the amount of light incident is relatively high and surface roughness of the solar panels attached to an area where the amount of light incident is relatively low The surface roughness of can be controlled differently.

In the solar power generation system, the plurality of solar panels may include double-sided light-receiving solar cell modules having an oxide-metal-oxide (OMO) electrode structure.

In the photovoltaic power generation system, the module comprises: a first transparent electrode layer formed on a substrate; a photoelectric conversion layer formed on the first transparent electrode layer; and a second transparent electrode layer formed on the photoelectric conversion layer, wherein at least a portion of an upper surface of the first transparent electrode layer is etched to control haze of the solar cell module, and the second transparent electrode layer is etched. The electrode layer may include a structure in which a first oxide layer, a metal layer, and a second oxide layer are sequentially stacked.

In the solar power generation system, the photoelectric conversion layer may include a structure in which a p-type semiconductor layer, an I-type semiconductor layer, and an N-type semiconductor layer are sequentially stacked.

According to the embodiment of the present invention made as described above, improved permeability is achieved by using a silver oxide transparent electrode that is non-toxic, can be manufactured in a large area, has excellent reliability even during long-term operation, and has excellent transmittance and electrical conductivity. It is possible to provide a photovoltaic power generation system using a double-sided light-receiving solar cell module having Of course, the scope of the present invention is not limited by these effects.

1 is a diagram schematically illustrating the structure of a double-sided light-receiving solar cell module used in a photovoltaic power generation system according to an embodiment of the present invention.
2 to 5 are diagrams schematically illustrating the structure of a double-sided light-receiving solar cell module attached to a building to explain a photovoltaic power generation system according to an embodiment of the present invention.
6 is a result of measuring the surface morphology of a ZnO:Al thin film for each etching time in a double-sided light-receiving solar cell sample according to an experimental example of the present invention.
7 is a result of analyzing the optical characteristics of a ZnO:Al thin film according to etching time in a double-sided light-receiving solar cell sample according to an experimental example of the present invention.
8 is a result of analyzing photoelectric conversion characteristics and short-circuit current characteristics according to illumination intensity at which light is incident for each etching time of a ZnO:Al thin film of a double-sided light-receiving solar cell sample according to an experimental example of the present invention.
9 is a result of analyzing the resistance characteristics according to the incident light intensity for each etching time of the ZnO:Al thin film of the double-sided light-receiving solar cell sample according to the experimental example of the present invention.
10 is a result of measuring the external quantum efficiency (EQE) and the open circuit voltage (Voc) according to the etching time of the ZnO:Al thin film of the double-sided light-receiving solar cell sample according to the experimental example of the present invention.
11 is a result of measuring electrical characteristics (J/I _L , α _E , and J _Loss ) according to etching time of the ZnO:Al thin film of a double-sided light-receiving solar cell sample according to an experimental example of the present invention.
12 is a result of analyzing the microstructure according to the etching time of the ZnO:Al thin film of the double-sided light-receiving solar cell sample according to the experimental example of the present invention.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art, and the following examples may be modified in many different forms, and the scope of the present invention is as follows It is not limited to the examples. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the spirit of the invention to those skilled in the art.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present invention.

Conventionally, the photoelectric conversion efficiency of a solar cell module is measured based on 1 sun (amount of light perpendicularly incident on a solar cell: 100 mW/cm 2 ). However, light is seldom incident vertically on a building, and accordingly, it is inevitable to operate under conditions of relatively low illumination. Due to this, there is a problem in that the photoelectric conversion efficiency is lower than the measured photoelectric conversion efficiency of the solar cell module.

In order to solve this problem, the present invention tried to provide a photovoltaic power generation system capable of obtaining maximum photoelectric conversion efficiency by measuring and comparing the efficiency of the solar cell module at various illuminances.

1 is a diagram schematically illustrating the structure of a double-sided light-receiving solar cell module used in a photovoltaic power generation system according to an embodiment of the present invention.

Referring to FIG. 1 , the double-sided light-receiving solar cell module 100 has a structure in which a first transparent electrode layer 10, a photoelectric conversion layer 20, and a second transparent electrode layer 30 are sequentially stacked on a substrate 40. includes Here, the photoelectric conversion layer 20 may include, for example, a hydrogenated amorphous silicon (a-Si:H) thin film layer. The hydrogenated amorphous silicon is a non-toxic material, can be manufactured in a large area, and has excellent reliability.

The substrate 40 is made of a transparent material such as glass or polymer. In addition, any transparent material can be used to transmit light. The first transparent electrode layer 10 is formed on the substrate 40, and the deposition method is a sputtering method, an electron beam method, an ion plating method, a screen printing method, a chemical vapor deposition (CVD) method, a spray pyrolysis method (SPD), Any one of deposition methods such as the pyrosol method may be used.

For the photoelectric conversion layer 20 , for example, a hydrogenated amorphous silicon (a-Si:H) thin film layer may be formed on the first transparent electrode layer 10 using plasma enhanced chemical vapor deposition (PECVD). Here, the photoelectric conversion layer 20 may be formed as a thin film layer having the same shape according to the surface structure of the first transparent electrode layer 10 .

The photoelectric conversion layer 20 includes a P-type semiconductor layer 22 , an I-type semiconductor layer 24 and an N-type semiconductor layer 26 . For example, hydrogenated amorphous silicon can control the P-type or N-type conductivity. Therefore, a PN junction structure may be formed by preparing the hydrogenated amorphous silicon in P-type and N-type. However, since it is an amorphous semiconductor, the carrier mobility is small and the recombination lifetime is short, so the diffusion length of minority carriers is about 0.1 μm to 1 μm, and a sufficient photovoltaic effect cannot be expected in a PN junction structure using only diffusion.

Therefore, a PIN junction structure is formed with an I-type semiconductor layer 24 having a thickness of about 0.5 μm interposed between the PN junction structures. The I-type semiconductor layer 24 has a high resistance, and electrons and holes generated according to light are quickly transferred to the P-type semiconductor layer 22 and the N-type semiconductor layer, respectively, by the internal electric field applied to the I-type semiconductor layer 24. (26).

In addition, since there is no long-range order in atomic arrangement in hydrogenated amorphous silicon, wavenumber conservation is not required during optical transition. Therefore, compared to crystalline silicon, which requires the help of phonons for wavenumber preservation in the indirect transition type, since it has a large absorption coefficient at the high energy axis of the absorption edge, it is possible to form a thin photoelectric conversion layer 20 with a thickness of about 0.5 μm.

The lower surface of the P-type semiconductor layer 22 is in contact with the upper surface of the first transparent electrode layer 10 , and the upper surface of the N-type semiconductor layer 26 is in contact with the lower surface of the second transparent electrode layer 30 . Here, the type of the transparent electrode layer in contact with the P-type semiconductor layer 22 and the N-type semiconductor layer 26 may be different depending on the manufacturing process.

The first transparent electrode layer 10 may use, for example, a transparent conductive oxide such as ZnO:Al (Al doped zinc oxide), ITO (Indium Tin Oxide), FTO (Florine doped Tin Oxide), or the like. The transparent conductive oxide is used as the first transparent electrode layer 10, but when the first transparent electrode layer 10 is made of a structurally hard material, that is, when it is made of a material resistant to external shocks for BIPV, the first transparent electrode layer (10) It can be used for electrodes and substrates.

At least a portion of the upper surface of the first transparent electrode layer 10 may be textured. The double-sided light-receiving solar cell module 100 improves photoelectric conversion efficiency by using a light trapping structure. The light trapping structure may generate more light-generated current by increasing a path length of light for light absorption. That is, the output current is improved by effectively scattering incident light by texturing at least a portion of the surface of the first transparent electrode layer 10 . In general, in order to increase the efficiency of the double-sided light-receiving solar cell module 100, haze is increased at an incident part where light is incident to scatter light so that the light is absorbed as much as possible. Therefore, the photoelectric conversion efficiency of the double-sided light-receiving solar cell module 100 tends to increase as the haze increases.

As described above, the photoelectric conversion efficiency of the double-sided light-receiving solar cell module 100 is measured based on 1 sun. However, there are not many cases in which light is substantially vertically incident on the surface of the double-sided light-receiving solar cell module 100 . Rather, the photoelectric conversion time of the double-sided light-receiving solar cell module 100 is longer at a relatively lower illuminance than the 1sun standard, and the power generated at this time will be greater. Conventionally, only a method of always increasing the haze of the double-sided light-receiving solar cell module 100 has been proposed under the premise that the higher the haze on a 1-sun basis, the higher the photoelectric conversion efficiency.

On the other hand, in the present invention, it can be confirmed that the photoelectric conversion efficiency increases as the haze of the double-sided light-receiving solar cell module 100 decreases at a low illuminance of less than 1 sun. This is due to recombination of electrons and holes due to defects in the photoelectric conversion layer 20 due to the surface roughness of the first transparent electrode layer 10 rather than increased light collection due to an increase in the time for forming texturing at low illumination of less than 1 sun. It is believed that more losses occur. That is, the light trapping structure having high surface roughness hinders uniform and perfect growth of the active layer, and thus generated carriers recombine within the thin film, causing defects that unintentionally reduce output current.

Here, the surface texturing of the first transparent electrode layer 10 may form a desired haze by controlling an etching time using, for example, 0.5 mol% hydrochloric acid (HCl). The etching time is differently controlled according to the thickness of the first transparent electrode layer 10, and also differently controlled according to the type of etching solution.

On the other hand, the second transparent electrode layer 30 has an oxide-metal-oxide (OMO structure) stacked structure, and includes a first AZO thin film 32, a silver oxide (AgOx) thin film 34 and a second AZO thin films 36 may be sequentially stacked. An OMO structure in which multi-layer electrodes with highly conductive metal thin films are inserted between transparent conductive oxide layers can be fabricated using a relatively low-temperature process compared to the formation of conventional electrodes.

The second transparent electrode layer 30 may be formed using, for example, a sputtering method. First, forming a first AZO thin film 32 on the photoelectric conversion layer 20 using an aluminum-doped zinc oxide (AZO) target, forming the first AZO thin film 32 using a silver (Ag) target Forming a silver oxide (AgOx) thin film 34 on the silver oxide (AgOx) thin film 34 and forming a second AZO thin film 36 on the silver oxide (AgOx) thin film 34 using an aluminum-doped zinc oxide (AZO) target. can include

The sputtering method includes depositing a silver oxide (AgOx) thin film 34 on the photoelectric conversion layer 20 by supplying a process gas into a chamber and applying a high voltage to a silver (Ag) target, wherein the process gas As a mixture, a mixed gas of an inert gas and an oxygen gas is used, and the partial pressure of the oxygen gas in the process gas may be 5% to 20%. Here, the inert gas includes argon, nitrogen or a mixed gas thereof.

On the other hand, the partial pressure of oxygen gas in the process gas is controlled in the range of 5% to 20% to form the silver oxide thin film 34, but the thickness of the first AZO thin film 32 and the second AZO thin film 36 Accordingly, the thickness of the silver oxide thin film 34 can be controlled, and the conductivity and transmittance are respectively changed by the partial pressure of the oxygen gas. Therefore, the partial pressure of the oxygen gas in the process gas is adjusted according to the thickness of the multilayer thin films constituting the second transparent electrode layer 30, and may be preferably 10% to 15%, more preferably 11% to 14%. may be in the range of

The first AZO thin film 32 and the second AZO thin film 36 are aluminum (Al) doped zinc oxide thin films (AZO), and in some cases, the first transparent electrode layer 10 used as a front electrode layer You can also use the same material as

The silver oxide thin film 34 uses, for example, silver (Ag) having the lowest resistivity among metals, but includes silver (Ag) doped with a predetermined amount of oxygen, not pure silver (Ag). This can be expressed as AgOx, where x is an arbitrary real number and varies depending on the content of oxygen.

Meanwhile, the conductivity and transmittance of the second transparent electrode layer 30 having the OMO structure are determined by the thicknesses of the first AZO thin film 32, the silver oxide thin film 34, and the second AZO thin film 36. Here, the silver oxide thin film 34 is the most important element, and has high light transmittance and excellent electrical characteristics compared to the conventionally used silver (Ag) thin film.

In the early stages of silver (Ag) particle growth, silver metal atoms are formed as separate islands. However, at a certain critical thickness, electrical resistance and light absorption rapidly increase with decreasing thickness of the silver (Ag) thin film. For example, if the thickness is greater than this critical thickness, the electrical resistance decreases according to the thickness of the silver (Ag) thin film, but the transmittance rapidly drops due to the strong reflection of the silver (Ag) thin film in the visible and near infrared regions. In order to solve this problem, by doping an oxygen component in the silver (Ag) thin film, the transmittance in the visible light wavelength band is improved without significant loss of electrical properties.

Depending on the content of oxygen doped in the silver oxide thin film 34, silver (Ag) and an oxide of silver (Ag), for example, Ag ₂ O or AgO, may coexist. In the case of silver (Ag), as a metal having a large surface energy, it forms a spherical island shape in a stable state in order to minimize surface energy during thin film growth. In this case, it acts as a limiting point in reducing the thickness of the thin film and simultaneously increases the surface roughness of the thin film. In the present invention, when depositing a silver (Ag) thin film in order to suppress such island growth, oxygen gas may be supplied as a reactive gas.

The double-sided light-receiving solar cell module 100 having the above-described structure may be formed on at least a part of the outer wall of a building and used as a photovoltaic power generation system for BIPV.

2 to 5 are diagrams schematically illustrating the structure of a double-sided light-receiving solar cell module attached to a building to explain a photovoltaic power generation system according to an embodiment of the present invention.

Referring to FIG. 2, the photovoltaic power generation system is composed of a plurality of photovoltaic panels, and the plurality of photovoltaic panels are, for example, a double-sided light-receiving solar cell module having an oxide-metal-oxide (OMO) electrode structure ( 100) may be included. The plurality of solar panels may be formed on at least a partial outer wall area of the building 200 . Here, the surface roughness of the plurality of solar panels is different depending on the position where they are attached to the building 200, and the plurality of solar panels can be connected in series according to the type and efficiency of the module, or the current can be connected in parallel. That is, the surface roughness of the plurality of solar panels is different depending on the difference between the surface roughness of the solar panel attached to the area where the light incident amount is relatively high and the surface roughness of the solar panel attached to the area where the light incident amount is relatively low. will be controlled Controlling the surface roughness differently is determined according to the arrangement direction of the building 200 . A detailed description of this will be described later with reference to FIGS. 3 to 5 below. Here, since the structure of the double-sided light-receiving solar cell module 100 is the same as that of FIG. 1 , only the substrate 40 and the first transparent electrode layer 10 are shown in FIGS. 3 to 5 for convenience.

Referring to FIG. 3, when viewed from the top of the building 200, when the direction of the building 200 is in the south direction, the number of solar panels toward the center from the edge of the outer wall of the building 200 The double-sided light-receiving solar cell module 100 having a plurality of OMO electrode structures may be formed on the outer wall of the building 200 so that the surface roughness is relatively high. Referring to an enlarged drawing of the double-sided light-receiving solar cell module 100 attached to the building 200, the central portion of the building 200 where light is incident vertically and the highest amount of light is collected, that is, the center of the building 200 The surface roughness of the first transparent electrode layer 10 formed on the substrate 40 may be designed to be relatively low as it goes from the central portion toward the edge of the outer wall.

Referring to FIG. 4, when viewed from the side of the building 200, the surface roughness of the plurality of solar panels is relatively high from the lower layer to the upper layer of the outer wall of the building 200 so that the plurality of outer walls of the building 200 are relatively high. A double-sided light-receiving solar cell module 100 having two OMO electrode structures may be formed. Referring to the enlarged drawing of the double-sided light-receiving solar cell module 100 attached to the building 200, the upper part of the building 200 where the highest amount of light is collected, that is, from the upper part of the building 200 to the lower part It can be designed so that the surface roughness of the first transparent electrode layer 10 formed on the substrate 40 becomes relatively low.

Referring to FIG. 5, when viewed from the top of the building 200, when the direction of the building 200 is southeast or southwest, from one edge of the outer wall of the building 200 to the other edge. The double-sided light-receiving solar cell module 100 having a plurality of OMO electrode structures may be formed on the outer wall of the building 200 so that the surface roughness of the plurality of solar panels becomes relatively high toward . Referring to the enlarged drawing of the double-sided light-receiving solar cell module 100 attached to the building 200, the outer part of the building 200 where light is incident vertically and the highest amount of light is collected, that is, the outer part of the building 200 The surface roughness of the first transparent electrode layer 10 formed on the substrate 40 may be designed to be relatively low as it goes from an edge portion located on one side of the outer wall to an edge portion located on the opposite side.

Here, the double-sided light-receiving solar cell module 100 having the roughest surface roughness may be disposed based on a position where sunlight is vertically incident on the building 200 when the sun is positioned in the south direction. In addition, the photovoltaic power generation system is designed so that the sum of the photoelectric conversion efficiencies satisfies the maximum value by arranging the double-sided light-receiving solar cell module 100 having a gradually lower surface roughness from the position outside the standard to the farther position. can do.

Hereinafter, in order to help understanding of the present invention, experimental examples for confirming the change in photoelectric conversion efficiency according to the incident light intensity will be described. However, the following experimental examples are only for helping understanding of the present invention, and the present invention is not limited to the following experimental examples.

<Experimental example>

A 1 μm-thick ZnO:Al thin film (Al 1 wt%) was deposited on soda lime glass having a thickness of 1.8 mm (50 × 50 mm 2 ) by DC pulse magnetron sputtering. Thereafter, the surface of the ZnO:Al thin film was etched using a 0.5 mol% HCl solution, and at this time, the etching time was controlled to 5s, 10s, 15s, and 20s, respectively. p ⁺ -a-SiOx:H (5nm), pa-SiOx:H (10nm), i ⁺ -a-Si:H (20nm) on a substrate equipped with a ZnO:Al thin film etched and textured under each etching condition ), ia-Si:H (280 nm), na-SiOx:H (5 nm), n-μc-SiOx:H (30 nm), ZnO: Al (50 nm), Ag (8 nm) and ZnO: Al (50 nm) The double-sided light-receiving solar cell samples each having an OMO electrode structure were fabricated by sequential deposition. Here, the hydrogenated amorphous silicon thin film was performed in a multi-chamber cluster system, and the P-type hydrogenated amorphous silicon thin film layer was formed using a mixture of dopant gases of B ₂ H ₆ , PH ₃ and CO ₂ under a frequency condition of 13.56 MHz. deposited A type I hydrogenated amorphous silicon thin film layer was deposited using a SiH ₄ source gas diluted with H ₂ under a very high frequency condition of 40.68 MHz. Then, an N-type SiOx thin film layer was deposited with the same mixture of gases that formed the P-type hydrogenated amorphous silicon thin film layer. The OMO electrode structure was formed by the DC pulsed magnetron sputtering method.

Thereafter, for each experimental sample, the optical properties of the etched ZnO:Al thin film were measured using an ultraviolet-visible spectrophotometer (Cary 5000, Varian), and the thickness of each thin film was measured using an ellipsometer.

The electrical properties of the ZnO:Al thin film were measured using a 4-probe system (MCP-T600, Mitsubishi Chemical Company), and the surface morphology of the thin film was measured using an atomic force microscope (AFM, NX10, Park System) and a field emission transmission electron microscope ( JEM-2100F HR, JEOL Ltd.).

In addition, the external quantum efficiency of the solar cell was measured using a quantum efficiency measurement system (IQE-200, Newport Co.), and the efficiency was measured using a solar simulator (Oriel 300, Newport Co.) and a source meter (Keithley 2400). (h), open circuit voltage (VOC) and short circuit current density (JSC) were analyzed and measured under standard recommended AM1.5G front incident and light-emitting diode (LED) illumination.

6 is a result of measuring the surface morphology of a ZnO:Al thin film for each etching time in a double-sided light-receiving solar cell sample according to an experimental example of the present invention.

First, referring to FIG. 6, it can be seen that the surface roughness of the ZnO:Al thin film increases as the etching time increases. The size and density of the crater shape can be controlled by the etching time, and the surface of the chemically etched thin film can effectively scatter light. This could also be confirmed through the graphs shown in (B) and (C) of FIG. 3 . As a result of chemical etching, the average surface roughness (R _avg ) and surface area of the ZnO:Al thin films increased from 18.4 nm to 41.67 nm and from 102.02 μm ² to 116.27 μm ² , respectively.

7 is a result of analyzing the optical characteristics of a ZnO:Al thin film according to etching time in a double-sided light-receiving solar cell sample according to an experimental example of the present invention.

First, referring to (A) of FIG. 7, it shows similar average transmittance (T _avg ) in the visible light wavelength band regardless of the etching time, and when each sample varies from 0 s to 20 s, 74.8 %, 73.8 %, 73.7 %, 73.6% and 73.4% are shown. Compared to the sample without etching, it was confirmed that the surface roughness of the ZnO:Al thin film increased as the etching time increased, and the light scattering effect increased accordingly.

In addition, as shown in (B) of FIG. 7, the haze value increased to 3.4%, 8.8%, 11.6%, and 14.6%, respectively, in the visible light wavelength band (400 nm to 600 nm) as the etching time increased. . Therefore, since light scattering can increase the light path or capture light in the photovoltaic layer and improve the absorbance of light in the solar cell, more light-generated carriers are expected to be generated.

On the other hand, referring to (C) of FIG. 7, as the etching time increased, the thickness of the ZnO:Al thin film decreased from 1110 nm to 963 nm, but the sheet resistance increased from 6.89 Ω/□ to 8.48 Ω/□. Although this has an optical advantage due to the light trapping effect due to etching of the ZnO:Al thin film, it was confirmed that excessive etching of the ZnO:Al thin film may cause unwanted electrical loss of the front transparent electrode. Therefore, both optical gain and electrical loss must be considered in order to obtain optimal photoelectric conversion characteristics of a solar cell.

8 is a result of analyzing photoelectric conversion characteristics and short-circuit current characteristics according to illumination intensity at which light is incident for each etching time of a ZnO:Al thin film of a double-sided light-receiving solar cell sample according to an experimental example of the present invention.

First, referring to FIG. 8 , it was confirmed that the type of sample having the highest photoelectric conversion efficiency was different according to the etching time according to the illuminance of the incident light. That is, the highest photoelectric conversion efficiency was measured in the sample in which the etching time was 20 s under the condition of 1.0 sun. On the other hand, the highest photoelectric conversion efficiency was measured in the sample with an etching time of 10 s under the condition of 0.1 sun. At this time, it was confirmed that the short circuit current density (J _SC ) exhibited the most similar operation to the photoelectric conversion efficiency (PCE) as shown in (B) of FIG. 5 . Since light trapping in solar cells is generally known to increase light absorption, the J _SC value should increase with the amount of light trapping or the etching time. However, the operation of the J _SC shown in (B) of FIG. 5 is not described in light trapping properties, and it is determined that other mechanisms are further included. This will be described in detail below based on other analysis results.

9 is a result of analyzing the resistance characteristics according to the incident light intensity for each etching time of the ZnO:Al thin film of the double-sided light-receiving solar cell sample according to the experimental example of the present invention.

First, referring to (A) of FIG. 9 , it can be seen that the shunt resistance (R _sh ) decreases as the etching time increases. Under the 1 sun condition, the value of the shunt resistance is small (that is, the current loss is large), but the change in the shunt resistance is much smaller for the difference in light trapping compared to low illumination. Therefore, the photoelectric conversion efficiency and short-circuit current under the 1 sun condition increased as expected due to the light trapping effect.

However, as the light intensity decreases, the change in the shunt resistance increases and the photoelectric conversion efficiency increases, and the short-circuit current depends more on the value of the shunt resistance (current loss) than the light trapping effect. Therefore, it can be confirmed that the maximum photoelectric conversion efficiency and short-circuit current under the condition of less than 1.0 sun are obtained not from the maximum light trapping structure (the structure with the roughest surface roughness of the ZnO: Al thin film), but from a structure in which the light intensity and shunt resistance value are balanced. could

It was confirmed that the shunt resistance behavior for this light intensity appeared better when normalized to the resistance value measured in a solar cell manufactured without a light trapping structure (a structure manufactured without etching the ZnO:Al thin film). . As shown in (B) of FIG. 9, the value of the normalized shunt resistance increases linearly according to the intensity of incident light of the light trapping structure, and the slope also tends to increase as the etching time increases. That is, this means that the loss of the value of the shunt resistor can be serious under low illumination conditions, and thus it can be confirmed that the photoelectric conversion characteristics of the solar cell can be significantly affected.

10 is a result of measuring the external quantum efficiency (EQE) and the open circuit voltage (Voc) according to the etching time of the ZnO:Al thin film of the double-sided light-receiving solar cell sample according to the experimental example of the present invention. Here, the external quantum efficiency (EQE) means a ratio of the external quantum efficiency (EQE) measured at a reverse bias voltage of -1V to the external quantum efficiency (EQE) at a zero bias voltage in a wavelength range of 400 nm to 780 nm.

Referring to (A) of FIG. 10 , it was confirmed that defects and relative current loss increased as the etching time increased. In addition, since the recombination loss was relatively uniformly observed in the entire wavelength band, it was confirmed that defects existed in the entire photoelectric conversion layer. Here, the recombination dynamics can be confirmed by the dependence of the open-circuit voltage (Voc) of the solar cell on the light intensity, as shown in FIG. In general, the value of n for the diode current component is 1 for the diffusion current and 2 for the recombination current of the diode junction. Referring again to (B) of FIG. 10 , it was confirmed that the extracted n value increased from 1.87 to 2.01 as the etching time increased from 5s to 20s, and accordingly, as the etching time increased, the current loss due to recombination increased. I could see this growing.

11 is a result of measuring electrical characteristics (J/I _L , α _E , and J _Loss ) according to etching time of the ZnO:Al thin film of a double-sided light-receiving solar cell sample according to an experimental example of the present invention.

Referring to FIG. 11 , it was confirmed that the J/I _L curve was saturated as the light intensity ( _IL ) increased, and the saturation value increased with etching time while the inflection point moved to the right. When the absorbance (α _E ) and the loss parameter (J _Loss ) are extracted as shown in (B) of FIG. 11 using the J/I _L curve shown in (A) of FIG. 11, the solar cell as the etching time increases. It shows that the total absorbance of increases, but the current loss can increase as the number of defects increases as the etching time increases.

12 is a result of analyzing the microstructure according to the etching time of the ZnO:Al thin film of the double-sided light-receiving solar cell sample according to the experimental example of the present invention.

Referring to FIG. 12, no defects were found in the sample in which etching was not performed, but in the sample in which etching was performed for 20 s, fine cracks were found in the a-Si:H layer, which is a photoelectric conversion layer. It was confirmed that losses may occur due to It was confirmed again that this coincided with the external quantum efficiency results shown in FIG. 10 . That is, when silicon atoms are deposited on a rough surface, fine cracks can be observed near the boundary of the growing cluster, which is reported as a defect that creates a recombination process of light-generated carriers. In addition, as shown in FIG. 6, it is determined that the number of defects increases due to the effect of increasing the interfacial area as the etching time increases. In summary, as the interfacial area of the solar cell active layer widens, the number of shunt paths increases due to defects such as voids, stacking faults, and atomic mismatches, and dangling bonds are formed at the interface to generate current. that has to be taken into account.

As described above, by changing the haze by adjusting the etching time of the ZnO:Al thin film, how the photoelectric conversion efficiency changes according to the incident illuminance (light amount) was examined through an experimental example. At this time, it was confirmed that the haze conditions for obtaining the maximum efficiency were different for each illuminance. At low illumination of 0.1 sun, the lower the etching time, the highest photoelectric conversion efficiency was obtained. On the other hand, at high illumination of 1 sun, the longer the etching time, the highest photoelectric conversion efficiency was obtained. It is judged that the loss due to recombination of electrons and holes due to defects in the solar cell occurs more due to the roughness of the thin film surface than the increased light capture due to etching at low illumination. When applied to a photovoltaic power generation system, it was confirmed that a higher maximum photovoltaic power generation performance than before can be obtained only when the surface roughness of each photovoltaic panel is arranged to have a relatively different surface roughness depending on the location where it is attached to the building.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

10: first transparent electrode layer
20: photoelectric conversion layer
22: P-type semiconductor layer
24: I-type semiconductor layer
26: N-type semiconductor layer
30: second transparent electrode layer
32: first oxide layer
34: metal layer
36: second oxide layer
40: substrate
100: double-sided light-receiving solar cell module
200: Architecture

Claims (8)

A solar power generation system consisting of a plurality of solar panels,
The plurality of solar panels are formed on at least a part of the outer wall area of the building,
The surface roughness of the plurality of solar panels is different depending on the position attached to the building,
solar power system. According to claim 1,
The surface roughness of the plurality of solar panels increases relatively from the edge of the outer wall of the building toward the central portion,
solar power system. According to claim 1,
The surface roughness of the plurality of solar panels is relatively high from one edge of the outer wall of the building to the other edge,
solar power system. According to claim 1,
The surface roughness of the plurality of solar panels increases relatively from the lower layer to the upper layer of the outer wall of the building,
solar power system. According to claim 1,
The surface roughness of the plurality of solar panels is differently controlled according to the difference between the surface roughness of the solar panel attached to the area where the light incident amount is relatively high and the surface roughness of the solar panel attached to the area where the light incident amount is relatively low. doing,
solar power system. According to claim 1,
The plurality of solar panels include a double-sided light-receiving solar cell module having an oxide-metal-oxide (OMO) electrode structure,
solar power system. According to claim 6,
The module is
A first transparent electrode layer formed on the substrate;
a photoelectric conversion layer formed on the first transparent electrode layer; and
A second transparent electrode layer formed on the photoelectric conversion layer; includes,
Controlling the haze of the solar cell module by etching at least a portion of the upper surface of the first transparent electrode layer;
The second transparent electrode layer includes a structure in which a first oxide layer, a metal layer, and a second oxide layer are sequentially stacked.
solar power system. According to claim 7,
The photoelectric conversion layer includes a structure in which a p-type semiconductor layer, an I-type semiconductor layer, and an N-type semiconductor layer are sequentially stacked.
solar power system.

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