JP2012182177A - Photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable photoelectric conversion device enhancing adhesive strength between an electrode and a light absorption layer.SOLUTION: A photoelectric conversion device 20 includes: an electrode 2 including molybdenum; and a light absorption layer 31 provided on the electrode 2 and including oxygen and selenium. Further, the light absorption layer 31 in the present embodiment has a plurality of first crystal grains and a plurality of second crystal grains, including the oxygen and the selenium. Further, the first crystal grains and the second crystal grains in the present embodiment are in contact with the electrode 2. In the present embodiment, the second crystal grains have a molar concentration of the oxygen at a portion in contact with the electrode 2 higher than that of the oxygen at a portion where the first crystal grains are in contact with the electrode 2.

Description

  The present invention relates to a photoelectric conversion device.

  Research and development has been progressing on chalcopyrite photoelectric conversion devices used for photovoltaic power generation and the like because they are relatively low cost and easy to increase in area.

  In this chalcopyrite photoelectric conversion device, soda lime glass is usually used as a substrate, and a molybdenum (Mo) thin film is formed thereon as a lower electrode. The photoelectric conversion device further includes a chalcogen compound semiconductor layer (chalcopyrite semiconductor layer) such as copper indium gallium diselenide (CIGS) as a light absorption layer and a mixed crystal compound semiconductor such as cadmium sulfide as a buffer layer. ing.

At this time, a molybdenum selenide (MoSe ₂ ) layer is formed at the interface between the Mo thin film electrode and the CIGS light absorption layer (see, for example, Patent Document 1).

JP 2002-319686 A

The adhesive strength between such a MoSe ₂ layer and the light absorbing layer described above is relatively good. However, when a plurality of MoSe ₂ layers are formed in a state where the c-axis is perpendicular to the surface of the Mo thin film electrode, the adhesive strength between the MoSe ₂ layers decreases, peeling occurs between the MoSe ₂ layers, and light absorption occurs. In some cases, the layer peeled off the electrode.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a highly reliable photoelectric conversion device by increasing the adhesive strength between an electrode and a light absorption layer.

  A photoelectric conversion device according to an embodiment of the present invention includes an electrode including molybdenum and a light absorption layer including oxygen and selenium provided on the electrode. Further, in the present embodiment, the light absorption layer has a plurality of first crystal grains and a plurality of second crystal grains containing the oxygen and the selenium. Further, in the present embodiment, the first crystal grain and the second crystal grain are in contact with the electrode. In the present embodiment, in the second crystal grain, the molar concentration of oxygen in the portion in contact with the electrode is larger than the molar concentration of oxygen in the portion in contact with the electrode of the first crystal grain.

According to the photoelectric conversion device according to one embodiment of the present invention, since excessive generation of MoSe ₂ occurring at the interface between the second crystal grains of the light absorption layer and the electrode can be reduced, peeling between the layers of MoSe ₂ is performed. Occurrence of peeling of the light absorption layer from the electrode, which can be caused by the above, can be reduced. As a result, in this embodiment, the reliability can be improved by increasing the adhesive strength between the electrode and the light absorption layer.

It is a top view which shows typically the structure of the photoelectric conversion apparatus which concerns on one Embodiment of this invention. It is sectional drawing in the position shown with the dashed-dotted line II-II in FIG. It is sectional drawing in the position shown with the dashed-two dotted line III-III in FIG. It is sectional drawing which expanded and showed typically the light absorption layer of the photoelectric conversion apparatus which concerns on one Embodiment. It is sectional drawing which expanded and showed typically the light absorption layer of the photoelectric conversion apparatus which concerns on other embodiment. It is sectional drawing which shows the mode in the middle of manufacture of the photoelectric conversion apparatus which concerns on one Embodiment. It is sectional drawing which shows the mode in the middle of manufacture of the photoelectric conversion apparatus which concerns on one Embodiment. It is sectional drawing which shows the mode in the middle of manufacture of the photoelectric conversion apparatus which concerns on one Embodiment. It is sectional drawing which shows the mode in the middle of manufacture of the photoelectric conversion apparatus which concerns on one Embodiment. It is sectional drawing which shows the mode in the middle of manufacture of the photoelectric conversion apparatus which concerns on one Embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, parts having the same configuration and function are denoted by the same reference numerals, and redundant description is omitted in the following description. Further, the drawings are schematically shown, and the sizes, positional relationships, and the like of various structures in the drawings are not accurately illustrated. 1 to 10 are provided with a right-handed XYZ coordinate system in which the arrangement direction of photoelectric conversion cells 10 (the horizontal direction in the drawing in FIG. 1) is the X-axis direction.

<(1) Schematic configuration of photoelectric conversion device>
<(1-1) Schematic configuration of photoelectric conversion device>
As illustrated in FIGS. 1 to 3, the photoelectric conversion device 20 includes a substrate 1 and a plurality of photoelectric conversion cells 10 arranged in a plane on one main surface of the substrate 1. Adjacent photoelectric conversion cells 10 are separated by a separation groove P3. That is, in the photoelectric conversion device 20, a plurality of photoelectric conversion cells 10 are arranged on one main surface of the substrate 1 through the separation groove portion P <b> 3 along a predetermined arrangement direction (+ X direction in the present embodiment). In FIG. 1, the separation groove portion P <b> 1 is seen through the top surface for convenience of illustration, and is indicated by a dotted line. In FIG. 1, only a part of the three photoelectric conversion cells 10 is shown. However, in the photoelectric conversion device 20, a large number (for example, eight) of photoelectric conversion cells 10 may be arranged in a plane (two-dimensionally) in the horizontal direction of the drawing. For example, electrodes for obtaining a voltage and a current by power generation can be provided at both ends in the X-axis direction of the photoelectric conversion device 20. In the photoelectric conversion device 20, for example, a large number of photoelectric conversion cells 10 may be arranged in a matrix.

  Further, for example, a mode in which the shape of the upper surface of each photoelectric conversion cell 10 is approximately rectangular and the shape of the upper surface of the photoelectric conversion device 20 is approximately square may be employed. In addition, the shape of the upper surface of each photoelectric conversion cell 10 does not need to be substantially rectangular, and may be other shapes. Moreover, the shape of the upper surface of the photoelectric conversion device 20 does not have to be generally square, and may be other shapes. However, in the photoelectric conversion device 20, the conversion efficiency is improved if a large number of photoelectric conversion cells 10 are arranged in a high-density plane.

  The conversion efficiency indicates a rate at which sunlight energy is converted into electric energy in the photoelectric conversion device 20. For example, the conversion efficiency can be derived by dividing the value of the electric energy output from the photoelectric conversion device 20 by the value of the energy of sunlight incident on the photoelectric conversion device 20 and multiplying by 100.

<(1-2) Basic configuration of photoelectric conversion cell>
Each photoelectric conversion cell 10 includes an electrode provided on the substrate 1 (hereinafter referred to as a lower electrode 2), a photoelectric conversion layer 3, and an electrode provided on the photoelectric conversion layer 3 (hereinafter referred to as an upper electrode 45). It has. Each photoelectric conversion cell 10 is provided with a separation groove P1 and a separation groove P2. In the photoelectric conversion device 20, the main surface on the side where the upper electrode 45 is provided is a light receiving surface.

  The substrate 1 supports a plurality of photoelectric conversion cells 10. Examples of the main material included in the substrate 1 include glass, ceramics, resin, and metal. Here, it is assumed that the substrate 1 is blue plate glass (soda lime glass) having a thickness of about 1 to 3 mm.

  The lower electrode 2 is a conductive layer provided on one main surface of the substrate 1 on the + Z side. The lower electrode 2 contains molybdenum. Further, the thickness of the lower electrode 2 is, for example, about 0.2 to 1 μm. The lower electrode 2 can be formed by a known thin film forming method such as a sputtering method or a vapor deposition method.

  The photoelectric conversion layer 3 is provided on the lower electrode 2 and includes a light absorption layer 31 and a buffer layer 32 that are sequentially stacked. Since the light absorption layer 31 and the buffer layer 32 are layers mainly including a semiconductor, the photoelectric conversion layer 3 is a layer mainly including a semiconductor (also referred to as a semiconductor layer).

  The light absorption layer 31 is provided on a main surface (also referred to as one main surface) on the + Z side of the lower electrode 2 and mainly includes a semiconductor having a first conductivity type (here, p-type conductivity type). . The thickness of the light absorption layer 31 is, for example, about 1 to 3 μm. The light absorption layer 31 mainly includes, for example, an I-III-VI group compound semiconductor having selenium. Thereby, the light absorption layer 31 can be thinned, and the conversion efficiency can be increased at a low cost with a small amount of material. The I-III-VI group compound semiconductor is a semiconductor mainly containing an I-III-VI group compound.

Here, as the I-III-VI group compound having selenium, a group I-B element (also referred to as a group 11 element), a group III-B element (also referred to as a group 13 element), and a group VI-B element (group 16). (Also referred to as an element). Examples of the I-III-VI group compounds include CuInSe ₂ (also referred to as copper indium selenide, CIS), Cu (In, Ga) Se ₂ (also referred to as copper indium diselenide, gallium, CIGS), and Cu. A material such as (In, Ga) (Se, S) ₂ (also referred to as diselene, copper indium gallium sulfide, gallium, or CIGSS) may be employed. Here, the light absorption layer 31 shall be demonstrated in the example which mainly contains CIGS.

  The light absorption layer 31 may be, for example, a thin film of a multicomponent compound semiconductor such as copper indium selenide / gallium having a thin film mainly containing diselen / copper indium sulfide / gallium as a surface layer.

  The light absorption layer 31 can be formed by a vacuum process such as sputtering or vapor deposition. The light absorption layer 31 can also be formed by a process called a coating method or a printing method. In the application method or the printing method, for example, a complex solution of elements mainly contained in the light absorption layer 31 is applied on the lower electrode 2, and then drying and heat treatment are performed. By using a process called this coating method or printing method, the cost for manufacturing the photoelectric conversion device 20 can be reduced.

The buffer layer 32 is provided on the main surface (also referred to as one main surface) on the + Z side of the light absorption layer 31, and has a second conductivity type (here, n) different from the first conductivity type of the light absorption layer 31. Mainly including a semiconductor having a conductive type). Note that semiconductors having different conductivity types are semiconductors having different conductive carriers. Moreover, the conductivity type of the light absorption layer 31 may be n-type, and the conductivity type of the buffer layer 32 may be p-type. Here, a heterojunction region is formed between the light absorption layer 31 and the buffer layer 32. For this reason, in the photoelectric conversion cell 10, photoelectric conversion can occur in the light absorption layer 31 and the buffer layer 32 that form the heterojunction region.

The buffer layer 32 mainly includes a compound semiconductor. Examples of the compound semiconductor included in the buffer layer 32 include cadmium sulfide (CdS), indium sulfide (In ₂ S ₃ ), zinc sulfide (ZnS), zinc oxide (ZnO), indium selenide (In ₂ Se ₃ ), In (OH, S), (Zn, In) (Se, OH), (Zn, Mg) O, and the like may be employed. If the buffer layer 32 has a resistivity of 1 Ω · cm or more, the generation of leakage current can be suppressed. The buffer layer 32 can be formed by, for example, a chemical bath deposition (CBD) method or the like.

  The buffer layer 32 has a thickness in the normal direction (+ Z direction) of one main surface of the light absorption layer 31. This thickness is set to, for example, 10 to 200 nm. If the thickness of the buffer layer 32 is 100 to 200 nm, the buffer layer 32 is less likely to be damaged when the transparent conductive layer 4 is formed on the buffer layer 32 by a sputtering method or the like.

  The upper electrode 45 is provided on the + Z side main surface (also referred to as one main surface) of the buffer layer 32. The upper electrode 45 includes a translucent conductive layer 4 and a grid electrode portion 5.

  The translucent conductive layer 4 is provided on one main surface of the buffer layer 32 and is, for example, a transparent conductive layer (also referred to as a transparent conductive layer) having an n-type conductivity. The translucent conductive layer 4 serves as an electrode (also referred to as an extraction electrode) that extracts charges generated in the photoelectric conversion layer 3. The translucent conductive layer 4 mainly includes a material having a lower resistivity than the buffer layer 32. The translucent conductive layer 4 may include what is called a window layer, and may include a window layer and a transparent conductive layer.

The translucent conductive layer 4 mainly includes a material having a wide forbidden band, transparent, and low resistance. As such a material, for example, a metal oxide semiconductor such as zinc oxide (ZnO), a compound of zinc oxide, indium oxide containing tin (ITO), and tin oxide (SnO ₂ ) can be employed. The zinc oxide compound only needs to contain any one element of aluminum, boron, gallium, indium, and fluorine.

  The translucent conductive layer 4 can be formed by a sputtering method, a vapor deposition method, a chemical vapor deposition (CVD) method, or the like. The thickness of the translucent conductive layer 4 may be, for example, 0.05 to 3.0 μm. Here, if the translucent conductive layer 4 has a resistivity of less than 1 Ω · cm and a sheet resistance of 50 Ω / □ or less, the photoelectric conversion layer 3 charges from the translucent conductive layer 4. Can be taken out well.

  If the buffer layer 32 and the light-transmitting conductive layer 4 have a property (also referred to as light transmittance) that allows light to easily pass through the wavelength band of light that can be absorbed by the light absorption layer 31, light absorption is achieved. A decrease in light absorption efficiency in the layer 31 can be suppressed. Moreover, if the thickness of the translucent conductive layer 4 is 0.05 to 0.5 μm, the light transmissivity in the translucent conductive layer 4 is enhanced, and at the same time, the current generated by the photoelectric conversion is satisfactorily transmitted. obtain. Further, if the absolute refractive index of the translucent conductive layer 4 and the absolute refractive index of the buffer layer 32 are substantially the same, the incidence caused by the reflection of light at the interface between the translucent conductive layer 4 and the buffer layer 32. Light loss can be reduced.

The grid electrode portion 5 is a linear electrode portion (also referred to as a linear electrode portion) provided on the main surface (also referred to as one main surface) on the + Z side of the translucent conductive layer 4. The grid electrode part 5 includes a plurality of current collecting parts 5a, connecting parts 5b, and hanging parts 5c. The plurality of current collectors 5a are separated in the Y-axis direction, and each current collector 5a extends in the X-axis direction. The connecting portion 5b is provided in the Y-axis direction, and each current collecting portion 5a is connected. The hanging part 5c is connected to the lower part of the connecting part 5b,
It connects with the lower electrode 2 extended | stretched from the adjacent photoelectric conversion cell 10 through the separation groove part P2.

  The current collector 5 a plays a role of collecting charges generated in the photoelectric conversion layer 3 and taken out in the translucent conductive layer 4. By providing the current collector 5a, the conductivity of the translucent conductive layer 4 is supplemented, so that the translucent conductive layer 4 can be thinned. As a result, it is possible to achieve both the securing of the charge extraction efficiency and the improvement of the light transmissivity in the translucent conductive layer 4. In addition, if the grid electrode part 5 mainly contains the metal excellent in electroconductivity, such as silver, the conversion efficiency in the photoelectric conversion apparatus 20 can improve. Moreover, as a metal contained in the grid electrode part 5, copper, aluminum, nickel etc. may be sufficient, for example.

  The electric charges collected by the translucent conductive layer 4 and the plurality of current collecting portions 5a are transmitted to the adjacent photoelectric conversion cell 10 through the connecting portion 5b and the hanging portion 5c. Thereby, in the photoelectric conversion apparatus 20, the adjacent photoelectric conversion cells 10 are electrically connected in series. Specifically, the drooping portion 5c electrically connected to the current collector 5a of the upper electrode 45 of one photoelectric conversion cell 10 and the lower electrode 2 of the other photoelectric conversion cell 10 are electrically connected. Are connected in series.

  Moreover, if the width | variety of the current collection part 5a is 50-400 micrometers, the fall of the incident amount of the light to the light absorption layer 31 may be suppressed, ensuring the favorable electroconductivity between the adjacent photoelectric conversion cells 10. FIG. The interval between the plurality of current collectors 5a provided in one photoelectric conversion cell 10 may be about 2.5 mm, for example.

<(1-3) Arrangement of separation groove and its role>
The separation groove P1 extends linearly in the Y-axis direction. By providing one or more separation grooves P1, the plurality of lower electrodes 2 are separated in the X-axis direction. In FIG. 2, three lower electrodes 2 are shown. An extending portion of the light absorption layer 31 provided immediately above is embedded in the separation groove P1. Thereby, the lower electrode 2 of one adjacent photoelectric conversion cell 10 and the lower electrode 2 of the other photoelectric conversion cell 10 are electrically separated. The width of the separation groove portion P1 may be, for example, about 50 μm to 400 μm, which is the same as the width of the grid electrode portion 5.

  The separation groove portion P2 is provided from one main surface of the translucent conductive layer 4 to the upper surface of the lower electrode 2, and extends linearly in the Y-axis direction. For this reason, the separation groove portion P2 separates the stacked portion in which the photoelectric conversion layer 3 and the translucent conductive layer 4 are stacked in the X-axis direction. That is, the separation groove P2 is provided so as to penetrate the photoelectric conversion layer 3 in a direction perpendicular to one main surface of the substrate 1.

  The separation groove portion P3 is provided from the upper surface of the photoelectric conversion cell 10 to the upper surface of the lower electrode 2, and extends in the Y-axis direction. The width of the separation groove P3 may be, for example, about 40 to 1000 μm.

  When the photoelectric conversion device 20 is viewed in plan from above the light receiving surface (here, + Z side), the separation groove P2 is provided between the separation groove P1 and the separation groove P3. In other words, the separation groove portion P1, the separation groove portion P2, and the separation groove portion P3 are provided in this order in the + X direction. Further, in each photoelectric conversion cell 10, the photoelectric conversion layer 3 is provided from above the lower electrode 2 to beyond the separation groove P <b> 1 and to the upper part of the adjacent lower electrode 2. Here, the adjacent lower electrode 2 is the lower electrode 2 extending from the adjacent photoelectric conversion cell 10.

When the photoelectric conversion device 20 is seen through from above the light receiving surface (here, + Z side), the photoelectric conversion device 20 includes the separation groove portion P1 and the separation groove portion P2, and includes the separation groove portion P1 and the separation groove portion P2. There are a region sandwiched between (also referred to as a connection region), a region sandwiched between the separation groove P2 and the separation groove P3, and a remaining region. For example, as shown in FIG. 3, this remaining region is a region contributing to power generation (also referred to as a power generation contribution region). On the other hand, for example, as shown in FIG. 3, a region sandwiched between the separation groove P2 and the separation groove P3 is a region that does not contribute to power generation (also referred to as a non-power generation contribution region).

<(1-4) Detailed structure of light absorption layer>
The light absorption layer 31 has a plurality of crystal grains as shown in FIG. And this crystal grain contains oxygen. The crystal grains 31A are a mixture of CIGS and oxygen mainly contained in the light absorption layer 31. Such crystal grains 31 </ b> A have a portion in contact with the lower electrode 2. A MoSe ₂ layer is formed at the interface between the crystal grains 31A containing oxygen and the lower electrode 2 containing molybdenum. If MoSe ₂ is excessively generated and a plurality of layers are formed to increase the thickness in the + Z direction, the MoSe ₂ is likely to be peeled off. In such a case, the light absorption layer 31 is easily peeled off from the lower electrode 2.

In the present embodiment, the crystal grain 31 </ b> A has two types of crystal grains (first crystal grain and second crystal grain) having different oxygen molar concentrations at the portion in contact with the lower electrode 2. At this time, the average crystal grain size of the first crystal grains and the second crystal grains may be, for example, 0.1 to 2 μm. The molar concentration of oxygen in the second crystal grains is larger than the molar concentration of oxygen in the first crystal grains. Therefore, MoSe ₂ generated at the contact portion between the second crystal grain and the lower electrode 2 is less than MoSe ₂ generated at the contact portion between the first crystal grain and the lower electrode 2. That is, in the present embodiment, excessive generation of MoSe ₂ generated at the interface between the second crystal grains of the light absorption layer 31 and the lower electrode 2 is reduced. Therefore, in this embodiment, it is possible to reduce the occurrence of peeling of the light absorption layer 31 from the lower electrode 2 that may be caused by peeling between the MoSe ₂ layers. As a result, in this embodiment, the reliability can be improved by increasing the adhesive strength between the lower electrode 2 and the light absorption layer 31.

  In the present embodiment, the molar concentration of oxygen in the second crystal grains in the portion in contact with the lower electrode 2 is, for example, 8 to 12 mol%. Moreover, the molar concentration of oxygen of the first crystal grains in the portion in contact with the lower electrode 2 is, for example, 4 to 7 mol%. The molar concentration of oxygen in the second crystal grains is 1.5 to 2.5 times larger than the molar concentration of oxygen in the first crystal grains at the portion in contact with the lower electrode 2. The molar concentration of oxygen in the first crystal grains and the second crystal grains is determined by, for example, energy dispersive X-ray analysis (EDS: Energy Dispersive x-ray) while observing a cross section of the light absorption layer 31 on the XZ plane with an electron microscope. Spectroscopy) may be used for measurement. The molar concentration of oxygen described above may be measured by, for example, Auger Electron Spectroscopy (AES).

  And the molar concentration of oxygen is calculated as follows, for example. First, for 60 arbitrary crystal grains of the light absorption layer 31, the molar concentration of oxygen at a site in contact with the lower electrode 2 is measured. Next, the molar concentration of oxygen in these crystal grains is plotted, and a graph showing the distribution of the molar concentration of oxygen is created. Next, it is divided into two groups consisting of 20 or more crystal grains. At this time, in these groups, the other group having an average oxygen molar concentration 1.5 to 2.5 times higher than the average oxygen molar concentration in one group is a group of second crystal grains.

Further, in the present embodiment, the molar concentration of selenium in the second crystal grains in the portion in contact with the lower electrode 2 may be smaller than the molar concentration of selenium in the first crystal grains in the portion in contact with the lower electrode 2. Thus, in the present embodiment can reduce the excessive production of MoSe ₂ occurring at the interface between the second crystal grains and the lower electrode 2. At this time, the molar concentration of selenium in the second crystal grains in the portion in contact with the lower electrode 2 is 35 to 40 mol%. On the other hand, the molar concentration of selenium in the first crystal grains in the portion in contact with the lower electrode 2 is 45 to 50 mol%. The molar concentration of selenium in the second crystal grains only needs to be about 20% smaller than the molar concentration of selenium in the first crystal grains in the portion in contact with the lower electrode 2. The molar concentration of selenium in the first crystal grains and the second crystal grains can be measured by the same method as the molar concentration of oxygen described above.

In the present embodiment, the ratio of the area occupied by the second crystal grains per unit area in the region of the light absorption layer 31 in plan view may be 3% to 10%. Note that the unit area, for example, may be a ² order of 10 to 1000 mm. Thereby, in this embodiment, when the separation groove part P2 and the separation groove part P3 are formed by mechanical scribing using a scribe needle, it becomes difficult to prevent scanning of the scribe needle, so that productivity is improved. Specifically, as described above, the MoSe _{2 at} the interface between the lower electrode 2 and the light absorption layer 31 is easily peeled off from the lower electrode 2 as the thickness thereof increases. Therefore, in the mechanical scribe in which the light absorption layer 31 is peeled from the lower electrode 2 to form the separation groove portion P2 and the separation groove portion P3, the separation groove portion described above can be formed relatively easily. In addition, the ratio of the area occupied per unit area of the 2nd crystal grain in the area | region which planarly viewed the light absorption layer 31 can be confirmed from a microscope picture. Specifically, for example, after taking a photograph of the surface of the light absorption layer 31 (XY plane in FIG. 4) using a microscope, the first crystal grains and the second crystal grains are colored by using image processing software. What is necessary is just to identify and calculate the occupation area of each crystal grain.

  Next, another embodiment of the photoelectric conversion device of the present invention will be described. As shown in FIG. 5, the present embodiment is different from the above-described embodiment in that it includes a light absorption layer 31 having first crystal grains and second crystal grains having different average crystal grain sizes. For this reason, in the present embodiment, as in the above-described embodiment, there is a difference in the molar concentration of oxygen between the first crystal grains and the second crystal grains.

  In the present embodiment, the average crystal grain size of the second crystal grain 31Aa is larger than the average crystal grain size of the first crystal grain. In FIG. 5, for convenience of illustration, only the second crystal grains are denoted by reference numerals, and crystal grains other than the second crystal grains 31 </ b> Aa correspond to the first crystal grains. In the present embodiment, the average crystal grain size of the first crystal grains may be 0.1 to 1 μm. On the other hand, the average crystal grain size of the second crystal grain 31Aa is 0.5 to 2 μm. That is, the average crystal grain size of the second crystal grain 31Aa is 2 to 20 times the average crystal grain size of the first crystal grain. Note that the average crystal grain size of each crystal grain can be obtained, for example, by entering the boundary of the crystal grain in a cross-sectional micrograph and then calculating it using image processing software. Specifically, it is only necessary to measure the particle diameter of 20 arbitrary first crystal grains and second crystal grains and calculate the average value.

  Thus, in this embodiment, since the average crystal grain size of the second crystal grain 31Aa is large, the contact area between the second crystal grain 31Aa and the lower electrode 2 is increased. Thereby, in this embodiment, since the second crystal grains 31Aa that are less likely to be peeled off from the lower electrode 2 than the first crystal grains are easily brought into contact with the lower electrode 2, the light absorption layer 31 is peeled off from the lower electrode 2. It becomes difficult.

  Further, the average crystal grain size of the second crystal grain 31Aa may be larger than the average thickness of the light absorption layer 31, as shown in FIG. With such a configuration, the light receiving area of the light absorption layer 31 in which the second crystal grain 31Aa is located can be increased, so that the conversion efficiency can be improved. Further, if the surface of the second crystal grain 31Aa protruding from the light receiving surface (upper surface on the + Z direction side) of the light absorption layer 31 formed of the first crystal grains is a curved surface, the light receiving area is further increased. Can be big. In addition, the average thickness of the light absorption layer 31 is 1-2 micrometers, for example.

<(2) Manufacturing process of photoelectric conversion device>
Here, an example of a manufacturing process of the photoelectric conversion device 20 having the above configuration will be described. Hereinafter, a case where the light absorption layer 31 is formed by using a coating method or a printing method and the buffer layer 32 is further formed will be described as an example. 6 to 10 are XZ cross-sectional views schematically showing a state in the process of manufacturing the photoelectric conversion device 20.

<(2-1) Formation of Lower Electrode 2>
First, as shown in FIG. 6, the lower electrode 2 mainly containing Mo or the like is formed on substantially the entire main surface of the cleaned substrate 1 by using a sputtering method or the like.

<(2-2) Formation of Separation Groove P1>
Next, a linear separation groove P <b> 1 is formed from a predetermined formation target position on the upper surface of the lower electrode 2 to the upper surface of the substrate 1 immediately below it. FIG. 7 is a view showing a state after the separation groove portion P1 is formed. The separation groove P1 can be formed, for example, by irradiating a predetermined formation target position while scanning with a YAG laser or other laser light.

<(2-3) Formation of photoelectric conversion layer 3>
Next, the light absorption layer 31 and the buffer layer 32 are sequentially formed on the lower electrode 2 to form the photoelectric conversion layer 3. FIG. 8 is a diagram illustrating a state after the photoelectric conversion layer 3 is formed.

  Here, the light absorption layer 31 can be formed by applying a predetermined solution to the surface of the lower electrode 2 and then sequentially performing drying and heat treatment. The predetermined solution can be prepared, for example, by dissolving a group IB metal and a group III-B metal directly in a solvent (also referred to as a mixed solvent) containing a selenium-containing organic compound and a basic organic solvent. In the predetermined solution, for example, the total concentration of the group I-B metal and the group III-B metal can be 10 wt% or more. As a method for applying the predetermined solution, various methods such as spin coater, screen printing, dipping, spraying, and die coater can be adopted.

  The selenium-containing organic compound is an organic compound containing a selenium element. As the selenium-containing organic compound, for example, selenol, selenide, diselenide and the like can be employed.

  Here, for example, as a method for forming the light absorbing layer 31, a method in which the following steps (i) to (iii) are mainly performed in order may be employed. (i) A mixed solvent is prepared by dissolving benzeneselenol so as to be 100 mol% with respect to pyridine. (ii) In this mixed solvent, the copper of the bare metal, the indium of the bare metal, the gallium of the bare metal, and the selenium of the bare metal are directly dissolved to prepare a solution. (iii) This solution is applied to the surface of the lower electrode 2 by a blade method, and then dried to form a film. The film is subjected to heat treatment in an atmosphere of hydrogen gas.

  In addition, the process in which a metal is directly dissolved in a mixed solvent is a process in which a simple metal or an alloy metal is directly mixed and dissolved in a mixed solvent. In this embodiment, the film is further dried for about 5 to 15 minutes in the presence of oxygen and about several ppm of moisture. In the film after this drying step, a plurality of cracks are generated in the depth direction of the film (the -Z direction in FIG. 8). As described above, since the drying step is performed in an oxygen atmosphere, oxygen enters a part of the film in contact with the lower electrode 2. Thereafter, heat treatment is performed in a reducing atmosphere. The reducing atmosphere may be any one of, for example, a nitrogen atmosphere, a hydrogen atmosphere, and a mixed gas atmosphere of hydrogen and nitrogen or argon. The heat processing temperature should just be 400-600 degreeC, for example. Through the above steps, the light absorption layer 31 having a plurality of crystal grains can be formed.

Further, the molar concentration of oxygen in the crystal grains at the site in contact with the lower electrode 2 depends on the presence or absence of the cracks described above. That is, in the portion in contact with the lower electrode 2, since the crystal grains (second crystal grains) located at the portion where the crack is generated take in oxygen from the outside through the crack, the crystal located at the portion where the crack is not generated The molar concentration of oxygen becomes larger than the grains (first crystal grains). Furthermore, with the manufacturing method described above, oxygen is taken into the second crystal grains, so that selenium near the lower electrode 2 is likely to volatilize, so that the molar concentration of selenium can be reduced.

  As another method, for example, in the film drying step, the film is partially dried in a short time using a heater or the like from the substrate 1 side, so that the selenium is partially volatilized to form a molar concentration of selenium. May form small crystal grains.

  In order to form the second crystal grain having an average crystal grain size larger than that of the first crystal grain as shown in FIG. 5, for example, the following may be performed. First, in the drying step of the film in the presence of oxygen, a distribution is generated in the molar concentration of selenium in the film near the lower electrode 2 by the above-described method through cracks or a method of partially volatilizing selenium. Then, the film is heat-treated at a high temperature rising rate. In addition, the temperature increase rate at this time is about 30 degreeC / min, and is set about 10-20 degreeC / min faster than usual. In a portion where the molar concentration of selenium is small, CuSe, which is a compound of copper and selenium, reacts with In, Ga and Se, and it is difficult to form a CIGS crystal. Since CuSe is present in the liquid phase during the heat treatment, CIGS grain growth can be further promoted, so that the average crystal grain size is increased. Further, in a portion where the molar concentration of selenium is small, a relatively large amount of oxygen is present compared to selenium. Therefore, the molar concentration of oxygen in the vicinity of the lower electrode 2 of the crystal grains (second crystal grains) having a large average crystal grain size can be made larger than the molar concentration of oxygen in the first crystal grains in the vicinity of the lower electrode 2.

  The buffer layer 32 is formed by a solution growth method (CBD method). For example, the buffer layer 32 mainly containing CdS is formed by immersing the substrate 1 in which the light absorption layer 31 has been formed in a solution prepared by dissolving cadmium acetate and thiourea in ammonia. Can be formed.

<(2-4) Formation of translucent conductive layer 4>
Next, the translucent conductive layer 4 is formed on the photoelectric conversion layer 3. FIG. 9 is a view showing a state after the translucent conductive layer 4 is formed. The translucent conductive layer 4 can be formed by sputtering, vapor deposition, chemical vapor deposition (CVD), or the like. For example, the transparent translucent conductive layer 4 mainly including zinc oxide to which aluminum is added is formed on the buffer layer 32.

<(2-5) Formation of Separation Groove P2>
Next, the separation groove P <b> 2 is formed in a region from the predetermined formation target position to the upper surface of the lower electrode 2 in the upper surface of the translucent conductive layer 4. FIG. 10 is a diagram illustrating a state after the separation groove portion P2 is formed. The separation groove portion P2 can be formed by mechanical scribing using a scribe needle. Note that the separation groove portion P2 may be formed by a laser beam in the same manner as the separation groove portion P1.

<(2-6) Formation of grid electrode portion 5>
Next, the grid electrode part 5 is formed from a predetermined formation target position on the upper surface of the translucent conductive layer 4 in which the separation groove part P2 is formed to the inside of the separation groove part P2. FIGS. 11A and 11B are views showing a state after the grid electrode portion 5 is formed.

  The grid electrode portion 5 is printed so that, for example, a metal paste in which a metal powder such as silver is dispersed in a resin binder or the like has the current collecting portion 5a and the connecting portion 5b, and the printed metal paste is dried. It can be formed by solidifying. At this time, the metal paste also enters the separation groove portion P2 and solidifies by drying, whereby the hanging portion 5c of the grid electrode portion 5 is formed. Solidification here means solidification after melting when the binder contained in the metal paste is a thermoplastic resin, and solidification by curing when the binder is a curable resin such as a thermosetting resin or a photocurable resin. And are included.

  Here, the connection part 5b of the grid electrode part 5 (upper electrode 45) is printed so that thickness becomes larger than another site | part. As this method, for example, the number of times of printing of the portion of the connecting portion 5b may be increased more than other portions. As another method, the metal paste may be printed more than other portions by slowing down the speed of the squeegee when printing the connecting portion 5b. Thereby, the thickness of the connection part 5b of the grid electrode part 5 in the + Z direction which is a direction perpendicular to one main surface of the substrate 1 is larger than the thickness of the other grid electrode part 5 part such as the current collecting part 5a. Become. In the metal paste printing process, printing may be performed once, or may be performed twice or more.

  As the metal paste, a paste having a silver content of 85 to 98 wt% and a resin component content of 2 to 15 wt% may be employed. For example, when the silver content in the metal paste is 88 to 92 wt%, viscosity suitable for printing and good conductivity can be obtained.

<(2-7) Formation of Separation Groove P3>
After the grid electrode portion 5 is formed, the separation groove portion P3 is formed in a region from the predetermined formation target position to the upper surface of the lower electrode 2 on the upper surface of the translucent conductive layer 4. Thereby, the photoelectric conversion apparatus 20 shown by FIGS. 1-4 is obtained. The separation groove part P3 can be formed by mechanical scribing using a scribe needle, like the separation groove part P2. At this time, the edge part of the grid electrode part 5 may be slightly shaved off.

  It should be noted that the present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the gist of the present invention.

1: Substrate 2: Lower electrode 3: Photoelectric conversion layer 31: Light absorption layer 31A: Crystal grain 31Aa: Second crystal grain 32: Buffer layer 4: Translucent conductive layer 5: Grid electrode part 5a: Current collector part 5b 5b1, 5b2: connecting part 5c: hanging part 10: photoelectric conversion cell 20: photoelectric conversion device 45: upper electrodes P1 to P3: separation groove part

Claims (5)

An electrode comprising molybdenum;
A light absorption layer containing oxygen and selenium provided on the electrode,
The light absorption layer includes a plurality of first crystal grains and a plurality of second crystal grains including the oxygen and the selenium,
The first crystal grains and the second crystal grains are in contact with the electrode;
The second crystal grain is a photoelectric conversion device, wherein a molar concentration of the oxygen in a portion in contact with the electrode is larger than a molar concentration of the oxygen in a portion in contact with the electrode of the first crystal grain.   2. The photoelectric conversion device according to claim 1, wherein the second crystal grain has a molar concentration of the selenium in a portion in contact with the electrode that is smaller than a molar concentration of the selenium in a portion in contact with the electrode of the first crystal grain.   3. The photoelectric conversion device according to claim 1, wherein an average crystal grain size of the second crystal grains is larger than an average crystal grain size of the first crystal grains.   The photoelectric conversion device according to claim 1, wherein the light absorption layer includes the second crystal grains having an average crystal grain size larger than an average thickness of the light absorption layer.   5. The photoelectric conversion according to claim 1, wherein the second crystal grains have an area ratio of 3% to 10% per unit area in a region of the light absorption layer in plan view. apparatus.

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