JP2011151135A - Photoelectric conversion module - Google Patents

Abstract

A photoelectric conversion module having improved durability while ensuring output characteristics is provided.
A photoelectric conversion device includes a photoelectric conversion cell, a protective layer provided on the surface of the photoelectric conversion cell and provided with a large number of needle-like crystals having an acid-receiving function, and a protective layer. And a sealing film including a resin having an ester bond.
[Selection] Figure 1

Description

  The present invention relates to a photoelectric conversion module.

  Photoelectric conversion modules used in solar cells and the like are generally arranged in parallel between a transparent protective member on the front surface side and a protective member on the rear surface side that receive light, with a sealing film on the front surface side and the back surface side. A plurality of photoelectric conversion cells are sealed. As the surface-side sealing film, for example, a film made of an ethylene vinyl acetate copolymer (EVA) having an ester bond is used from the viewpoint of ensuring high transparency.

  In such a photoelectric conversion module, EVA tends to be hydrolyzed over time due to permeation of moisture or water at a high temperature to generate acetic acid. This acetic acid may corrode the electrodes and elements of the photoelectric conversion cell. In view of this, a solar cell is proposed in which a sealing film on the surface side is formed by a composition in which an acid-accepting agent that traps acid is added to an ethylene-polar monomer copolymer (see, for example, Patent Document 1).

JP 2008-53377 A

  For a sealing film formed of a composition to which an acid acceptor or the like is added, if the amount of the acid acceptor added is large, the transparency is lowered, and if the amount of the acid acceptor is small, photoelectric conversion by an acid is performed. The function of preventing cell deterioration is insufficient. That is, it is difficult to achieve both ensuring of the output characteristics of the photoelectric conversion module and improvement of durability. And such a problem is common in the photoelectric conversion module generally sealed with the sealing film which has transparency.

  This invention is made | formed in view of the said subject, and it aims at providing the photoelectric conversion module which improved durability, ensuring output characteristics.

  In order to solve the above-described problem, the photoelectric conversion module according to the first aspect includes a photoelectric conversion cell and a large number of needle-like crystals having an acid-receiving function provided on the surface of the photoelectric conversion cell. And a sealing film including a resin having an ester bond provided on the protective layer.

  ADVANTAGE OF THE INVENTION According to this invention, the function of the deterioration prevention by acid reception is improved, ensuring transparency. Thereby, coexistence with the ensuring of the output characteristic in a photoelectric conversion module and the improvement of durability is achieved.

It is sectional drawing which shows the structure of a photoelectric conversion module. It is a top view which shows the structure of a photoelectric conversion apparatus. It is sectional drawing which shows the structure of a photoelectric conversion apparatus. It is a figure for demonstrating the structure of a protective layer. It is sectional drawing which shows the mode in the middle of manufacture of a photoelectric conversion apparatus. It is sectional drawing which shows the mode in the middle of manufacture of a photoelectric conversion apparatus. It is sectional drawing which shows the mode in the middle of manufacture of a photoelectric conversion apparatus. It is sectional drawing which shows the mode in the middle of manufacture of a photoelectric conversion apparatus. It is sectional drawing which shows the mode in the middle of manufacture of a photoelectric conversion apparatus. It is sectional drawing which shows the mode in the middle of manufacture of a photoelectric conversion apparatus. It is a figure which illustrates the specific formation aspect of a protective layer.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

<(1) Schematic configuration of photoelectric conversion module>
FIG. 1 is a cross-sectional view illustrating a schematic configuration of a photoelectric conversion module 20 according to an embodiment of the present invention.

  The photoelectric conversion module 20 has a configuration in which a protective layer 6, a sealing film 7, and a protective substrate 8 are sequentially stacked on a photoelectric conversion device 21 that receives light such as sunlight and generates electric power.

  The protective layer 6 is a layer provided on the light receiving surface side surface of the photoelectric conversion device 21 and having a function of capturing an acid (acid receiving function). The protective layer 6 has a structure in which a large number of needle crystals having an acid accepting function are arranged, and has a thickness of 0.5 μm to 2 μm, for example. The acicular crystal includes a crystal extending long in one direction such as a rod or a column with a sharp tip, in addition to a sharp tip. And since the protective layer 6 is comprised by the acicular crystal | crystallization which is crystalline, the light transmittance in the light-receiving surface side is maintained favorable. A specific configuration of the protective layer 6 and a method for forming the protective layer 6 will be described later.

  The sealing film 7 is a film provided on the protective layer 6 for sealing the photoelectric conversion device 21. The sealing film 7 as the sealing portion includes, for example, a portion made of a resin including an ester bond such as an ethylene vinyl acetate copolymer (EVA) from the viewpoint of ensuring transparency. The thickness of the sealing film 7 is preferably 1 mm or less from the viewpoint of preventing the occurrence of cracking due to stress load, and for example, 0.5 mm or 1 mm is preferably employed.

  By the way, although the resin having an ester bond constituting the sealing film 7 is gradually, it is hydrolyzed over time by permeation of moisture and / or water at a high temperature, and the acid (resin constituting the sealing film 7). Produces acetic acid if it contains EVA.

  With respect to the generation of this acid, in the photoelectric conversion module 20 according to the embodiment, the acid is captured by the protective layer 6 provided between the photoelectric conversion device 21 and the sealing film 7, and the photoelectric conversion device 21 is corroded. Is prevented.

  The protective substrate 8 is provided on the sealing film 7 and protects moisture and foreign matter from entering the photoelectric conversion module 20 from the outside. The protective substrate 8 is configured by, for example, a flat glass substrate.

<(2) Configuration of photoelectric conversion device>
FIG. 2 is a top view showing the configuration of the photoelectric conversion device 21. 3 is a cross-sectional view of the photoelectric conversion device 21 taken along section line III-III in FIG. 2, that is, an xz cross-sectional view of the photoelectric conversion device 21 at the position indicated by the one-dot chain line in FIG. 1 to 10, a right-handed xyz coordinate system in which the arrangement direction of photoelectric conversion cells 10 (the horizontal direction in the drawing in FIG. 2) is the x-axis direction is attached.

  The photoelectric conversion device 21 has a configuration in which a plurality of photoelectric conversion cells 10 are arranged in parallel on the substrate 1. In FIG. 2, only two photoelectric conversion cells 10 are shown for convenience of illustration, but in the actual photoelectric conversion device 21, in the horizontal direction of the drawing, or further in the vertical direction of the drawing perpendicular thereto, A large number of photoelectric conversion cells 10 are arranged in a plane (two-dimensionally).

  Each photoelectric conversion cell 10 mainly includes a lower electrode layer 2, a photoelectric conversion layer 3, an upper electrode layer 4, a grid electrode 5, and a connection portion 45. In the photoelectric conversion device 21, the main surface on the side where the upper electrode layer 4 and the grid electrode 5 are provided is the light receiving surface side. Further, the photoelectric conversion device 21 is provided with three types of groove portions, that is, a first groove portion P1, a second groove portion P2, and a third groove portion P3.

  The substrate 1 is for supporting a plurality of photoelectric conversion cells 10. Examples of the material used for the substrate 1 include glass, ceramics, resin, and metal. Here, a blue plate glass (soda lime glass) having a thickness of about 1 mm to 3 mm is used as the substrate 1.

  The lower electrode layer 2 is a metal such as Mo (molybdenum), Al (aluminum), Ti (titanium), Ta (tantalum), or Au (gold) provided on one main surface of the substrate 1, or these It is a conductor layer made of a metal laminate structure. The lower electrode layer 2 is formed to a thickness of about 0.2 μm to 1 μm using a known thin film forming method such as sputtering or vapor deposition.

  The photoelectric conversion layer 3 has a configuration in which a light absorption layer 31 and a buffer layer 32 are stacked.

  The light absorption layer 31 is a semiconductor layer having a p-type conductivity type and made of a chalcopyrite (also referred to as CIS) I-III-VI group compound provided on the lower electrode layer 2. The light absorption layer 31 has a thickness of about 1 μm to 3 μm.

Here, the I-III-VI group compound is a group IB 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 (also referred to as a group 16 element). ) And a compound. Examples of the I-III-VI group compound 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), Cu ( In, Ga) (Se, S) ₂ (also referred to as diselene, copper indium gallium sulfide, gallium, CIGSS). The light absorption layer 31 may be formed of a thin film of a multicomponent compound semiconductor such as copper indium selenide / gallium having a thin film of selenide / copper indium sulfide / gallium as a surface layer.

  The light absorption layer 31 may be a semiconductor layer made of a II-VI group compound. The II-VI group compound is a compound semiconductor of a group II-B (also referred to as a group 12 element) and a group VI-B element. However, I-III-VI compound semiconductors, which are chalcopyrite compound semiconductors, are preferably used from the viewpoint of reducing the layer thickness and increasing the photoelectric conversion efficiency at low cost with a small amount of material.

  The light absorption layer 31 can be formed by a so-called vacuum process such as sputtering or vapor deposition, and a complex solution of constituent elements of the light absorption layer 31 is applied on the lower electrode layer 2 and then dried and heat-treated. It can also be formed by a process called a coating method or a printing method. However, from the viewpoint of suppressing the manufacturing cost of the photoelectric conversion device 21, the latter process is preferably used.

  The buffer layer 32 is a semiconductor layer provided on the light absorption layer 31 and having an n-type conductivity type different from the conductivity type of the light absorption layer 31. The buffer layer 32 is provided in a mode of heterojunction with the light absorption layer 31 when the light absorption layer 31 is made of an I-III-VI group compound semiconductor. In the photoelectric conversion cell 10, photoelectric conversion occurs in the light absorption layer 31 and the buffer layer 32 constituting the heterojunction, and thus the light absorption layer 31 and the buffer layer 32 are the photoelectric conversion layer 3. In addition, the structure of the photoelectric converting layer 3 is not limited to this, The semiconductor layer of a different conductivity type may be a homojunction. Here, semiconductors having different conductivity types are semiconductors having different conductive carriers.

The buffer layer 32 is made of, for example, CdS (cadmium sulfide), In ₂ S ₃ (indium sulfide), ZnS (zinc sulfide), ZnO (zinc oxide), In ₂ Se ₃ (indium selenide), In (OH, S). , (Zn, In) (Se, OH), and (Zn, Mg) O. From the viewpoint of reducing leakage current, the buffer layer 32 preferably has a resistivity of 1 Ω · cm or more.

  The buffer layer 32 is preferably formed to a thickness of 10 nm to 200 nm, preferably 100 nm to 200 nm. Thereby, the fall of the photoelectric conversion efficiency in high temperature, high humidity conditions is suppressed especially effectively. The buffer layer 32 is formed by, for example, a chemical bath deposition (CBD) method.

  The upper electrode layer 4 is a transparent conductive film having an n-type conductivity type provided on the buffer layer 32. The upper electrode layer 4 is provided as an extraction electrode for charges generated in the photoelectric conversion layer 3. The upper electrode layer 4 is made of a material having a lower resistivity than the buffer layer 32. The upper electrode layer 4 includes what is called a window layer, and when a transparent conductive film is further provided in addition to the window layer, these can be regarded as the upper electrode layer 4 together.

The upper electrode layer 4 includes a wide bandgap, transparent, and low resistance material, such as ZnO (zinc oxide), zinc, a zinc oxide compound containing boron, boron, gallium, indium, fluorine, or the like. The metal oxide semiconductor is composed of at least one of indium oxide (ITO) and tin oxide (SnO ₂ ).

  The upper electrode layer 4 is formed to a thickness of 0.05 μm to 3.0 μm by sputtering, vapor deposition, chemical vapor deposition (CVD), or the like. And from a viewpoint of taking out an electric charge favorably from the photoelectric converting layer 3, it is preferable that the upper electrode layer 4 has a resistivity of less than 1 Ω · cm and a sheet resistance of 50 Ω / □ or less.

  It is preferable that the buffer layer 32 and the upper electrode layer 4 are made of a material having optical transparency with respect to the wavelength region of light absorbed by the light absorption layer 31. Thereby, the fall of the light absorption efficiency in the light absorption layer 31 by providing the buffer layer 32 and the upper electrode layer 4 is suppressed.

  From the viewpoint of enhancing the light transmittance, at the same time enhancing the effect of preventing the loss of light reflection and the light scattering effect, and further transmitting the current generated by the photoelectric conversion, the upper electrode layer 4 is 0.05 to The thickness is preferably 0.5 μm. Further, from the viewpoint of preventing light reflection loss at the interface between the upper electrode layer 4 and the buffer layer 32, it is preferable that the refractive indexes of the upper electrode layer 4 and the buffer layer 32 are equal.

  The grid electrodes 5 are provided apart from each other in the y-axis direction, and each of the current collectors 5a is connected to the plurality of current collectors 5a extending in the x-axis direction and extends in the y-axis direction. It is an electrode which has electroconductivity provided with connecting part 5b to do. The grid electrode 5 is made of a metal such as Ag, for example.

  The current collector 5 a plays a role of collecting charges generated in the photoelectric conversion layer 3 and taken out in the upper electrode layer 4. By providing the current collector 5a, the upper electrode layer 4 can be thinned. Since the upper electrode layer 4 is provided above the light absorption layer 31, it is desirable that the upper electrode layer 4 be formed as thin as possible in order to increase light transmission. However, as the thickness is reduced, the resistance increases. Efficiency is reduced. Therefore, by providing the current collector 5a, the charge extraction efficiency is ensured, and the light transmittance of the upper electrode layer 4 can be improved.

  The charges collected by the grid electrode 5 and the upper electrode layer 4 are transmitted to the adjacent photoelectric conversion cell 10 through the connection part 45 provided in the second groove part P2. The connection part 45 is comprised by the extension part 4a of the upper electrode layer 4, and the drooping part 5c from the connection part 5b formed on it. Thereby, in the photoelectric conversion device 21, one lower electrode layer 2 of the adjacent photoelectric conversion cell 10, the other upper electrode layer 4 and the grid electrode 5 are connected to each other by the connection portion 45 provided in the second groove portion P2. The connection conductor is electrically connected in series.

  The grid electrode 5 has a width of 50 μm to 400 μm from the viewpoint of minimizing the reduction in the light receiving area that affects the amount of light incident on the light absorption layer 31 while ensuring good conductivity. Is preferred.

  In addition, it is preferable that at least the surface of the connecting portion 5b of the grid electrode 5 is formed of a material that reflects light in the wavelength region absorbed by the light absorption layer 31. Such a configuration is, for example, by adding metal particles such as silver having a high light reflectivity to a translucent resin, or depositing a metal having a high light reflectivity such as aluminum on the surface of the connecting portion 5b. Etc. can be formed. In this case, when the photoelectric conversion device 21 is modularized, the light reflected by the connecting portion 5 b can be reflected again in the photoelectric conversion module 20 and can be incident again on the light absorption layer 31. As a result, the amount of incident light increases to the photoelectric conversion efficiency of the photoelectric conversion device 21.

  Preferably, at least the current collector 5a of the grid electrode 5 preferably includes solder. Thereby, about the grid electrode 5, while the tolerance with respect to a bending stress is improved, an electrical resistance can be reduced more.

  More preferably, the grid electrode 5 includes two or more kinds of metals having different melting points, is heated at a temperature at which at least one kind of metal is not melted, and is melted at least one other metal and then cured by cooling. And is preferably formed. In this case, since the metal having a low melting point is melted in the forming process, the grid electrode 5 is densified and the resistance is reduced. At that time, the spread of the molten metal is suppressed by the high melting point metal which is not melted.

<(3) Structure of protective layer>
FIG. 4 is a schematic diagram showing the configuration of the protective layer 6, focusing on a part of the protective layer 6 and its periphery.

  The protective layer 6 is configured by providing a large number of needle crystals 61 on the surface of the upper electrode layer 4, that is, the photoelectric conversion cell 10. That is, the protective layer 6 is an array in which a large number of needle crystals 61 are arrayed. FIG. 4 shows a state in which the needle-like crystals 61 are provided on the surface of the upper electrode layer 4. However, as shown in FIG. 1, many needle-like crystals are also provided on the surface of the grid electrode 5. A crystal 61 is provided.

The acicular crystal 61 is composed of a metal oxide having an acid accepting function. Examples of the metal oxide having an acid accepting function include ZnO (zinc oxide), MgO (magnesium oxide), and a mixture of zinc oxide and magnesium oxide. That is, the needle-like crystal 61 may be composed of a metal oxide crystal containing at least one metal oxide of ZnO and MgO, or a mixed crystal of ZnO and MgO (Zn _x Mg _{(1-x )} O [0 ≦ x ≦ 1]).

  In addition, when comparing ZnO and MgO, MgO is stronger in basicity than ZnO and has a higher ability to accept acids. In addition, the transmittance of ultraviolet rays is higher with MgO. However, MgO is easier to absorb water. For this reason, from the viewpoint of ensuring the water resistance of the needle-like crystal 61 and preventing the peeling of the protective layer 6 and utilizing the characteristics of both ZnO and MgO, the needle-like crystal 61 is composed of the ZnO crystal and the MgO crystal. And a mixed crystal of ZnO and MgO. Further, from the viewpoint of making the characteristics of the protective layer 6 uniform, the acicular crystal 61 is preferably composed of a mixed crystal of ZnO and MgO.

  Each of the acicular crystals 61 may extend in the same direction, or each may extend in a random direction. From the viewpoint of more effectively suppressing acid intrusion from the sealing film 7 to the photoelectric conversion cell 10, the needle-like crystals 61 extend in random directions and substantially cover the surface of the photoelectric conversion cell 10. It is good to be. Further, the acicular crystal 61 preferably has a high density on the photoelectric conversion cell 10 side. Thereby, the refractive index can be changed in the thickness direction of the protective layer 6 to suppress light loss due to reflection, and light can be advanced from the sealing film 7 through the protective layer 6 to the photoelectric conversion cell 10 with low loss. Can do. Therefore, the photoelectric conversion efficiency can be increased.

  Thus, the acicular crystal 61 having a high density on the photoelectric conversion cell 10 side includes, for example, the first acicular crystal 61A extending perpendicularly to the light receiving surface side surface of the photoelectric conversion cell 10 and the photoelectric conversion cell 10. The second acicular crystal 61B extends from the surface on the light receiving surface side in a direction inclined with respect to the normal direction of the surface.

  Specifically, the first acicular crystal 61A includes a plurality of spaced apart ones on the light receiving surface side surface of the photoelectric conversion cell 10 (specifically, the upper electrode layer 4 and the grid electrode 5). From each of the starting points 6p, an angle of about 90 ° is formed with respect to the surface on the light receiving surface side of the photoelectric conversion cell 10 and extends perpendicular to the surface on the light receiving surface side of the photoelectric conversion cell 10. The second acicular crystal 61B has a wider angle including a direction perpendicular to the light receiving surface side surface of the photoelectric conversion cell 10 (specifically, the upper electrode layer 4 and the grid electrode 5) from each of the plurality of starting points 6p. It extends in a direction within a range (for example, an angle with the surface on the light receiving surface side is 0 ° to 90 °). The length of the second needle crystal 61B is shorter than the length of the first needle crystal 61A. In the first and second acicular crystals 61A and 61B, the longitudinal direction and the c-axis coincide with each other, and each first acicular crystal 61A has substantially the same length.

  One or more first acicular crystals 61A and one or more second acicular crystals 61B extend from one starting point 6p. There is a gap between two adjacent first acicular crystals 61A. The tip of the second acicular crystal 61B extending from an arbitrary starting point 6p (on the side opposite to the starting point 6p) is an acicular crystal 61 (the first acicular crystal 61A or the second acicular crystal) extending from another starting point 6p adjacent to the starting point 6p. It is in contact with or close to the side surface of the needle-like crystal 61B).

  In addition, the protective layer 6 includes a lower region 6 a that constitutes a portion on the photoelectric conversion cell 10 side, and an upper region 6 b that constitutes a portion on the opposite side to the photoelectric conversion cell 10. The second acicular crystal 61B exists in the lower region 6a but does not exist in the upper region 6b in the direction perpendicular to the light receiving surface of the photoelectric conversion cell 10. For this reason, the ratio of the cross section (area) of the needle-like crystal 61 occupying a plane parallel to the light receiving surface of the photoelectric conversion cell 10 is higher in the lower region 6a than in the upper region 6b. In other words, the density (arrangement density) of the acicular crystals 61 (specifically, the first and second acicular crystals 61A and 61B) disposed in the lower region 6a is the acicular shape in the upper region 6b. The arrangement density of the crystals 61 (specifically, the first needle crystals 61A) is higher.

  The orientation of the needle crystal 61 is lower in the lower region 6a than in the upper region 6b. The acicular crystal 61 is generally c-axis oriented (at least in the upper region 6b) (the c-axis extends along a specific direction (the direction perpendicular to the light receiving surface of the photoelectric conversion cell 10), and the frequency is high). .

  An exposed portion of the surface of the photoelectric conversion cell 10 that is not covered with the first needle crystal 61A is substantially (completely) covered with the second needle crystal 61B. That is, the light-receiving side surface of the photoelectric conversion cell 10 is almost completely covered with the acicular crystals 61 (specifically, the first and second acicular crystals 61A and 61B). In other words, the entire surface of the photoelectric conversion cell 10 is covered with the needle crystal 61. Therefore, the sealing film 7 and the photoelectric conversion cell 10 are separated by the presence of the protective layer 6, and the sealing film 7 and the surface of the photoelectric conversion cell 10 are not in contact with each other.

  In FIG. 4, the length of the first needle crystal 61 </ b> A is shown to be about three times the length of the second needle crystal 61 </ b> B because of the illustrated relationship. From the viewpoint of separating the sealing film 7 and the photoelectric conversion cell 10, the distance between adjacent first needle crystals 61 </ b> A is preferably as short as 0.1 μm or less, for example. At this time, for example, the length of the first needle-like crystal 61A is 10 times or more of the length of the second needle-like crystal 61B, the thickness of the protective layer 6 is 0.5 μm to 2 μm, and the lower region The thickness of 6a is 50 nm or less.

  The acicular crystal 61 is an n-type semiconductor crystal made of, for example, ZnO. Between the photoelectric conversion cell 10 and the needle-like crystal 61 (mainly in the vicinity of the starting point 6p), there are a plurality of minute regions 9 made of zinc oxide crystals. The crystal orientation of each minute region 9 is random and does not necessarily coincide with the crystal orientation of the needle crystal 61.

  Since the protective layer 6 composed of the above-described array of needle crystals 61 has a large surface area in contact with the sealing film 7, it can capture more acid that can be generated in the sealing film 7. Moreover, since the disposition density of the needle-like crystals 61 in the lower region 6a is high, the invasion of the acid from the sealing film 7 to the photoelectric conversion cell 10 is more reliably prevented.

<(4) Manufacturing method of photoelectric conversion module>
Next, a method for manufacturing the photoelectric conversion module 20 having the above configuration will be described. Specifically, after the method for forming the photoelectric conversion device 21 is described, the method for forming the protective layer 6 will be described.

<(4-1) Method for Manufacturing Photoelectric Conversion Device>
Hereinafter, a case where the light absorption layer 31 made of an I-III-VI group compound semiconductor is formed using a coating method or a printing method, and the buffer layer 32 is further formed will be described as an example.

  5 to 10 are cross-sectional views showing a state in the middle of manufacturing the photoelectric conversion device 21. FIG. Note that the cross-sectional views shown in FIGS. 5 to 10 show a state in the middle of manufacturing a portion corresponding to the cross-section shown in FIG.

  First, as shown in FIG. 5, the lower electrode layer 2 made of Mo or the like is formed on the substantially entire surface of the cleaned substrate 1 using a sputtering method or the like. Then, the first groove portion P1 is formed from the linear formation target position along the Y direction on the upper surface of the lower electrode layer 2 to the upper surface of the substrate 1 immediately below the formation position. It is preferable that the first groove portion P1 is formed by scribe processing in which groove processing is performed by irradiating the formation target position while scanning with a YAG laser or other laser light. FIG. 6 is a diagram illustrating a state after the first groove portion P1 is formed.

  After the first groove portion P1 is formed, the light absorption layer 31 and the buffer layer 32 are sequentially formed on the lower electrode layer 2. FIG. 7 is a diagram illustrating a state after the light absorption layer 31 and the buffer layer 32 are formed.

  About the light absorption layer 31, the solution for forming the light absorption layer 31 is apply | coated to the surface of the lower electrode layer 2, and after forming a film | membrane by drying, this film | membrane is formed by heat-processing. The solution for forming the light absorption layer 31 directly dissolves the group IB metal and the group III-B metal in a solvent (also simply referred to as a mixed solvent) containing a chalcogen element-containing organic compound and a basic organic solvent. Thus, the total concentration of the group I-B metal and the group III-B metal is 10 wt% or more. For the application of this solution, various methods such as spin coater, screen printing, dipping, spraying, and die coater can be applied.

  The chalcogen element-containing organic compound is an organic compound containing a chalcogen element. The chalcogen element refers to S, Se, or Te among VI-B group elements. Examples of the chalcogen element-containing organic compound include thiol, sulfide, disulfide, selenol, selenide, diselenide and the like.

  For example, it is produced by directly dissolving bullion copper, bullion indium, bullion gallium, and bullion selenium in a mixed solvent in which benzeneselenol is dissolved to 100 mol% with respect to pyridine. A step in which the solution is applied by a blade method and dried to form a film, followed by heat treatment in an atmosphere of hydrogen gas is preferable.

  To directly dissolve a metal in a mixed solvent means to dissolve a single metal or alloy ingot directly into the mixed solvent and dissolve it. Drying is desirably performed in a reducing atmosphere. The drying temperature is, for example, 50 ° C to 300 ° C. The heat treatment is preferably performed in a reducing atmosphere so as to prevent oxidation and obtain a good I-III-VI compound semiconductor. The reducing atmosphere is desirably any of a nitrogen atmosphere, a forming gas atmosphere, and a hydrogen atmosphere. The heat treatment temperature is, for example, 400 ° C to 600 ° C.

  The buffer layer 32 is formed by a solution growth method (CBD method). For example, the buffer layer 32 made of CdS is formed in the light absorption layer 31 by immersing the substrate 1 in which cadmium acetate and thiourea are dissolved in ammonia and the light absorption layer 31 is formed. This process is a suitable example.

  After the light absorption layer 31 and the buffer layer 32 are formed, the second groove portion P2 extends from the linear formation target position along the Y direction on the upper surface of the buffer layer 32 to the upper surface of the lower electrode layer 2 immediately below the formation position. It is formed. The second groove portion P2 is formed, for example, by performing scribing using a scribe needle having a scribe width of about 40 μm to 50 μm continuously several times while shifting the pitch. Further, the second groove portion P2 may be formed by scribing after the tip shape of the scribe needle is expanded to an extent close to the width of the second groove portion P2. Alternatively, two or more scribe needles may be fixed in a state where they are in contact with each other or close to each other, and may be formed by performing scribing once to several times. FIG. 8 is a diagram illustrating a state after the second groove portion P2 is formed. The second groove portion P2 is formed at a position slightly shifted in the X direction from the first groove portion P1.

  After the second groove portion P2 is formed, the transparent upper electrode layer 4 mainly composed of indium oxide (ITO) containing tin, for example, is formed on the buffer layer 32. The upper electrode layer 4 is formed by sputtering, vapor deposition, CVD, or the like. FIG. 9 is a view showing a state after the upper electrode layer 4 is formed.

  After the upper electrode layer 4 is formed, the grid electrode 5 is formed. The grid electrode 5 is formed, for example, by printing a conductive paste in which a metal powder such as Ag is dispersed in a resin binder or the like in a pattern, drying it, and solidifying it. Solidification includes the solidified state after melting when the binder used in the conductive paste is a thermoplastic resin, and after curing when the binder is a curable resin such as a thermosetting resin or a photocurable resin. The state of is also included. FIG. 10 is a diagram illustrating a state after the grid electrode 5 is formed.

  After the grid electrode 5 is formed, a third groove portion P3 is formed from the linear formation target position on the upper surface of the upper electrode layer 4 to the upper surface of the lower electrode layer 2 immediately below the formation position. The width of the third groove portion P3 is preferably about 40 μm to 1000 μm, for example. Further, the third groove portion P3 is preferably formed by mechanical scribing similarly to the second groove portion P2. In this manner, the photoelectric conversion device 21 shown in FIGS. 2 and 3 is formed by forming the third groove P3.

<(4-2) Method for forming protective layer>
Next, a method for forming the protective layer 6 will be described. For the formation of the protective layer 6, the following forming method according to the technique proposed by the present applicant (see International Publication No. 2006/129650) can be used.

The protective layer 6 is formed by growing needle-like crystals 61 on the light receiving surface side surface of the photoelectric conversion device 21 by an electroless plating method using a predetermined plating solution. The predetermined plating solution is X ¹ OH (wherein X ¹ represents any one of Na, K and Cs), X ² ₂ CO ₃ (wherein X ² is any one of Na, K and Cs) A plating solution containing at least one alkali selected from the group consisting of NH ₃ and having a pH of 13 or more. In this electroless plating method, the needle-like crystal 61 grows using a substance having a hydroxyl group on the surface as a catalyst.

  The base of the region where the needle-like crystal 61 grows is a plurality of crystal grains, the crystal grains having random crystal orientations, and the requirement that the surface is hydrophilic and amorphous It satisfies. Note that when the base is formed of a plurality of crystal grains, an amorphous matrix may exist between the crystal grains. If any of these requirements is satisfied by the surface of the light receiving surface side of the photoelectric conversion device 21 to be plated (hereinafter also referred to as the plating target surface) itself, the surface of the plating target surface is used as a base. The acicular crystal 61 can be grown.

  In addition, before performing electroless plating, particles as a base satisfying any of the above requirements may be arranged on the surface to be plated. These particles are made of, for example, the same material as the minute region 9. In this case, in the step of performing electroless plating, the needle-like crystal 61 grows using the particles arranged as the base as nuclei (seed). In this case, the arrangement density of the growing acicular crystals 61 is controlled by the density of the arranged particles.

  In the case of performing electroless plating without arranging such particles on the surface to be plated, the material itself constituting the surface on the light receiving surface side of the photoelectric conversion device 21 is a substance having a hydroxyl group on the surface (OH in the structural formula). Whether it is a substance containing a group or a substance that forms an OH group on the surface when it comes into contact with water). On the other hand, when the electroless plating is performed after the particles as the base are arranged on the surface to be plated, the particles may be composed of a substance having a hydroxyl group on the surface, and the material itself constituting the surface to be plated is The substance may not be a substance having a hydroxyl group on the surface.

  The formation temperature of the needle-like crystal 61 by electroless plating is 60 ° C. to 100 ° C., preferably 70 ° C. to 90 ° C., and the surface to be plated as in the case where the CVD method or the pulse laser deposition method is adopted. Need not be held at high temperatures.

  According to this electroless plating method, a uniform array of acicular crystals 61 can be formed on the surface of the plating target having a complicated surface shape, and the acicular crystals 61 can be formed even if the surface of the plating target is not conductive. Can be formed.

  Further, according to the above formation method, the needle-like crystal 61 has a starting point on the surface of the plating target (if the forming method includes a step of arranging particles as a base on the surface of the plating target, this particle is the starting point). Therefore, acicular crystals 61 grow in various directions.

  If a method for forming acicular crystals such as a CVD method or an electrodeposition method is employed, most of the acicular crystals grow in a direction substantially perpendicular to the surface to be plated. When such a method is employed, the second acicular crystal 61B does not grow, and the lower region 6a having a high arrangement density of the acicular crystals 61 is not formed. Even when a protective layer having no lower region 6a is formed, acid can be received by the array of needle crystals 61A. The lower region 6a having a high arrangement density is preferably formed.

  When a plurality of starting points on which the acicular crystal grows are positioned apart from each other on the surface to be plated, the surface to be plated is exposed from among a large number of acicular crystals grown almost perpendicular to the surface to be plated. To do. On the other hand, according to the above forming method, the acicular crystal grown on the surface of the plating object substantially perpendicularly (so that the angle formed with the surface of the plating object is within a predetermined angle range) (on the first acicular crystal 61A). The exposed portion of the surface to be plated that is not covered by the substantially equivalent) is substantially completely formed by needle-like crystals (substantially equivalent to the second needle-like crystals 61B) that grow in a direction away from the direction perpendicular to the surface to be plated. Covered. That is, by the above formation method, it is possible to form the protective layer 6 capable of satisfactorily separating the photoelectric conversion device 21 and the sealing film 7.

  The direction in which the acicular crystal 61 grows also depends on the crystal orientation or crystallinity of the portion that is the starting point from which the acicular crystal 61 grows. For example, when the surface of the plating target has a hydroxyl group, the surface of the plating target can be a starting point for the growth of the needle-shaped crystal 61, but when the crystal orientation related to the surface of the plating target is aligned, Crystal orientation may be aligned.

  For this reason, it is preferable that the part from which the acicular crystal 61 grows exhibits crystallinity and has a random crystal orientation or does not exhibit crystallinity. For example, when the particle (substance having a surface hydroxyl group) made of the same material as that of the microregion 9 shows crystallinity and has a random crystal orientation or does not show crystallinity, The crystal orientation of the growing needle crystal 61 is random. However, even if the core particle has crystallinity, the crystal orientation of a certain particle does not necessarily match the crystal orientation of the needle crystal 61 that grows from the particle.

  When the acicular crystal 61 grows in a random direction, the adjacent acicular crystals 61 are sterically hindered and bonded to each other, and as a result, the lower region 6a substantially covers the surface to be plated. .

  Here, when the particles are arranged on the surface to be plated, for example, a colloidal solution in which particles (fine particles) serving as starting points for the growth of the needle-like crystals 61 are dispersed on the surface to be plated by dip coating, spray coating, spin coating, or When dropped, usually the crystal orientations of the particles are not aligned. As a result, particles having a random crystal orientation are arranged on the surface to be plated.

  Further, the second acicular crystal 61B that grows from an arbitrary starting point in a direction significantly different from the direction perpendicular to the surface to be plated is hindered by the acicular crystal 61 that grows from another adjacent starting point and grows longer. I can't. On the other hand, the first needle crystal 61A that grows in a direction substantially perpendicular to the surface to be plated can grow for a long time without being blocked by other needle crystals 61. In this way, the longitudinal direction of the acicular crystal 61 is aligned as the entire protective layer 6. Therefore, for example, when the longitudinal direction of the acicular crystal 61 and the c-axis coincide with each other, the array of acicular crystals 61 is c-axis oriented.

  Further, in order to substantially cover the surface to be plated with the protective layer 6 made of the needle-like crystals 61, it is necessary that the growth starting points exist to some extent. In the following, a method will be described in which the growth starting points are assumed to be particles (fine particles) and the growth starting points exist to a certain extent.

  When an array of acicular crystals 61 made of ZnO is formed, the growth starting particles (fine particles made of ZnO) are plated with, for example, an ethanol solution in which zinc acetate dihydrate (ZnO precursor) is dissolved. It is formed by spin-coating the target surface, heating (baking) the target surface for plating, and thermally decomposing zinc acetate. Here, depending on the heating temperature, fine particles made of amorphous ZnO and / or fine particles made of ZnO that are crystalline and random in crystal orientation are obtained. In addition, there may be a state in which an amorphous matrix made of ZnO exists between fine particles made of ZnO that are crystalline and have random crystal orientations.

  In this case, by adjusting the concentration of zinc acetate dihydrate in the ethanol solution to about 0.001 mol / liter to about 0.1 mol / liter, the acicular crystal 61 to be grown substantially covers the surface to be plated. Thus, fine particles made of ZnO can be densely present (for example, exist so as to form a thin film) as much as possible. When the concentration of zinc acetate dihydrate in the ethanol solution is too low, the density of fine particles formed on the surface to be plated becomes too low, and the needle-like crystals 61 do not substantially cover the surface to be plated. However, by increasing the number of times of spin coating and thermal decomposition, even if the concentration is 0.001 mol / liter or less, the acicular crystals 61 can be covered to the extent that the acicular crystals 61 cover the surface to be plated closely. It becomes possible to make the fine particles which become the growth starting point exist densely.

  However, in this case, the fine particles partially agglomerate and the acicular crystals 61 are formed on the agglomerated fine particles, and the adhesion strength between the surface to be plated and the acicular crystals 61 (that is, the protective layer 6) does not increase. For this reason, the surface to be plated may be exposed due to peeling of the acicular crystals 61 or the like. Therefore, the number of spin coating is preferably 1 to 5 times.

  Here, when the acicular crystal 61 made of ZnO grows, the fine particles made of ZnO are taken into the acicular crystal 61. For this reason, even if the acicular crystal and the surface to be plated are not in direct contact at the start of the growth of the acicular crystal 61, The surface to be plated can be in direct contact. When the growth of the acicular crystal 61 is completed, if the area where the acicular crystal 61 and the surface of the plating target are in direct contact is large to some extent, the adhesion strength between the surface of the plating target and the acicular crystal 61 is increased.

  However, when the concentration of zinc acetate dihydrate in the ethanol solution is higher than about 0.1 mol / liter, needle-like crystals 61 are formed on the aggregated fine particles. In this case, when the growth of the needle crystal 61 is completed, the contact area between the surface to be plated and the array of needle crystals 61 is reduced, or the surface of the plating object and the array of needle crystals 61 are not in contact with each other. . For this reason, the adhesion strength between the surface to be plated and the needle crystal 61 is lowered, and the needle crystal 61 is peeled off. As a result, the surface to be plated is exposed and the surface to be plated cannot be substantially covered with the array of needle-like crystals 61.

  If the heating temperature after spin-coating the ethanol solution in which zinc acetate dihydrate is dissolved on the surface to be plated is 180 ° C. to 500 ° C., fine particles made of ZnO are obtained on the surface to be plated. Even in this temperature range, when heating at a low temperature, the heating time required to obtain fine particles made of ZnO becomes long. If the salt (precursor) used is decomposed to obtain particles of the target material, hydrolysis, dehydration condensation, plasma irradiation can be used instead of thermal decomposition (including those by microwave heating). Etc. may be performed.

  In addition, when this forming method includes a step of arranging the particles on the surface to be plated, a part of the particles may remain as the minute region 9 after the growth of the acicular crystal 61 is completed. In this case, the adhesion between the acicular crystal 61 and the surface to be plated can be improved by the minute region 9. The adhesion strength between the surface to be plated and the array of needle crystals 61 can be controlled by the density of the particles arranged on the surface to be plated prior to electroless plating.

  Furthermore, in this formation method, for example, the length and density of the needle-like crystals 61 can be controlled by controlling the time for performing electroless plating. The needle-like crystal 61 may be repeatedly grown by a plurality of times of electroless plating.

  By the formation method described above, the protective layer 6 in which the needle crystals 61 are formed at a high density is formed. FIG. 11 is a diagram showing a specific example of an array of acicular crystals 61 composed of a large number of acicular crystals 61 formed by the above-described forming method. FIG. 11 shows a photograph (also referred to as an SEM photograph) obtained by photographing the array of needle crystals 61 from the side with a scanning electron microscope. Here, the thickness of the array of needle-like crystals 61 is about 1.2 μm to 1.3 μm, and the thickness of the array corresponding to the lower region 6a is 50 nm or less. The density of the first needle crystals 61A in the upper region 6b measured by the SEM photograph taken from the tip side of the first needle crystals 61A is, for example, 1000 or more per 1 μm × 1 μm projection area.

  Note that the sealing film 7 is formed on the protective layer 6 thus formed by, for example, heat-rolling and forming an EVA composition containing EVA and a crosslinking agent. Thereafter, the protective substrate 8 is laminated on the sealing film 7, and for example, the EVA is cured by crosslinking by heating and pressurizing at a temperature of about 135 ° C. to 180 ° C., and the sealing film 7 and the protective substrate 8 are bonded. Integrated. Thereby, the photoelectric conversion module 20 in which the photoelectric conversion device 21, the protective layer 6, the sealing film 7, and the protective substrate 8 are stacked and integrated is obtained.

<(5) Summary of one embodiment>
As mentioned above, in the photoelectric conversion module 20 which concerns on one Embodiment, the protective layer 6 which consists of the acicular crystal | crystallization 61 which has an acid accepting function is provided in the surface of the photoelectric conversion apparatus 21. FIG. The protective layer 6 captures an acid generated by hydrolysis of the sealing film 7 containing a resin having an ester bond. For this reason, generation | occurrence | production of the malfunction which an acid corrodes the photoelectric conversion apparatus 21 is prevented. In addition, since the acicular crystal 61 is crystalline, it has good light transmittance, and the protective layer 6 made of an array of acicular crystals 61 has a large surface area on the sealing film 7 side, and therefore more. It is possible to capture acid. Therefore, the function of preventing deterioration due to acid reception is enhanced while ensuring transparency. Thereby, coexistence with the ensuring of the output characteristic in the photoelectric conversion module 20 and a durable improvement is achieved.

  Furthermore, since the protective layer 6 is provided on the light receiving surface side of the photoelectric conversion cell 10, it also functions as an antireflection film. For this reason, it is possible to add an antireflection function without increasing the manufacturing cost.

  Further, from the viewpoint of more surely preventing acid from entering the photoelectric conversion cell 10 from the sealing film 7, the protective layer 6 is a lower region where the disposition density of the acicular crystals 61 is high on the photoelectric conversion cell 10 side. 6a is preferred. It is more preferable that the lower region 6 a substantially covers the surface of the photoelectric conversion cell 10, and that the sealing film 7 is not in contact with the surface of the photoelectric conversion cell 10 due to the presence of the protective layer 6. preferable.

<(6) Modification>
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.

  In the above embodiment, the case where the layer responsible for photoelectric conversion is mainly composed of a chalcopyrite-based I-III-VI group compound is described, but the present invention is not limited to this. For example, by providing a protective layer made of acicular crystals having an acid-accepting function between the photoelectric conversion cell and the sealing film, ensuring both output characteristics and improvement in durability in the photoelectric conversion module can The same can be realized in a photoelectric conversion module using a crystal substrate, a single crystal substrate, or other photoelectric conversion materials. Further, for example, the present invention can be applied to a back contact type photoelectric conversion device in which both an anode and a negative electrode are provided on the non-light-receiving surface side.

  Furthermore, for example, if a protective layer made of acicular crystals having an acid-receiving function is provided between the photoelectric conversion cell and the sealing film on the non-light-receiving surface side of the photoelectric conversion cell, the solar battery cell on the non-light-receiving surface side Corrosion is prevented.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower electrode layer 3 Photoelectric conversion layer 4 Upper electrode layer 5 Grid electrode 6 Protective layer 6a Lower region 6b Upper region 7 Sealing film 8 Protective substrate 10 Photoelectric conversion cell 20 Photoelectric conversion module 21 Photoelectric conversion device 31 Light absorption layer 32 Buffer layer 45 Connection portion 61 Acicular crystal 61A First acicular crystal 61B Second acicular crystal

Claims (8)

A photoelectric conversion cell;
A protective layer provided on the surface of the photoelectric conversion cell, on which a large number of needle-like crystals having an acid accepting function are disposed;
A sealing film containing a resin having an ester bond provided on the protective layer;
A photoelectric conversion module comprising: The photoelectric conversion module according to claim 1,
The acicular crystals are
A photoelectric conversion module comprising a metal oxide. The photoelectric conversion module according to claim 2,
The metal oxide is
A photoelectric conversion module comprising at least one metal oxide of zinc oxide and magnesium oxide. The photoelectric conversion module according to claim 2,
The acicular crystals are
A photoelectric conversion module comprising a mixed crystal of zinc oxide and magnesium oxide. The photoelectric conversion module according to any one of claims 1 to 4, wherein
The protective layer is
A first region constituting a portion on the opposite side of the photoelectric conversion cell; a first region constituting a portion on the photoelectric conversion cell side and having a higher density of acicular crystals than the first region; And a photoelectric conversion module having two regions. The photoelectric conversion module according to claim 5,
The second region is
A photoelectric conversion module characterized by substantially covering the surface of the photoelectric conversion cell. The photoelectric conversion module according to any one of claims 1 to 6, wherein
The sealing film is
The photoelectric conversion module, which is not in contact with the surface of the photoelectric conversion cell due to the presence of the protective layer. The photoelectric conversion module according to any one of claims 1 to 7,
The protective layer is
A photoelectric conversion module provided on a light receiving surface side surface of the photoelectric conversion cell.