JP2012186290A - Photoelectric conversion element and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion element at a low cost while improving characteristics of a solar cell.SOLUTION: There is provided a photoelectric conversion element 1 of a CIS solar cell comprising: a metal oxide semiconductor layer 4; a buffer layer 5 stacked on the metal oxide semiconductor layer 4 so as to contact the metal oxide semiconductor layer 4; and a light absorbing layer 6 stacked on the buffer layer 5 on a side opposite to the metal oxide semiconductor layer so as to contact the buffer layer 5. The buffer layer 5 is formed of an InSlayer to which another material is added, and is formed by spraying technique performed in the air. The other material added to the buffer layer should preferably be metal containing at least one element selected from a group of metallic elements including titanium (Ti), zinc (Zn), tin (Sn), niobium (Nb), yttrium (Y), lantern (La), zirconium (Zr), tantalum (Ta), hafnium (Hf), strontium (Sr), barium (Ba), calcium (Ca), vanadium (V), and tungsten (W), for example.

Description

  The present invention relates to a photoelectric conversion element and a method for manufacturing the photoelectric conversion element, and particularly relates to a photoelectric conversion element including a compound solar cell that obtains high photoelectric conversion efficiency and a method for manufacturing the photoelectric conversion element.

From the viewpoint of global warming and finite fossil fuel reserves, etc., energy resources have been reviewed, and as one of them, solar power generation, which is a clean power generation technology, has attracted attention. Solar energy is inexhaustible, there is no worry of exhaustion like fossil fuels, and there is no increase in CO ₂ .

  Currently, the mainstream photovoltaic power generation is silicon solar cells. However, since silicon solar cells are expensive to manufacture and it is difficult to depreciate the current cost of electricity, product development based on a free economy has not yet been made.

Accordingly, there is a need for a lower cost and higher efficiency solar cell, a thin film silicon solar cell with reduced silicon usage, a chalcogenide-based thin film solar cell such as Cu (In, Ga) Se ₂ , CuInS ₂ , and dye enhancement. Development of organic solar cells such as sensitive solar cells is underway.

Among them, Cu (In, Ga) Se ₂ and CuInS ₂ (hereinafter referred to as Cu (In, Ga) Se ₂ and CuInS ₂ are collectively referred to as CIS) as solar cells having a high possibility of replacing silicon solar cells. Chalcogenide-based thin film solar cells have been widely studied.

  However, most of the thin film fabrication processes used in current CIS solar cells use vacuum processes such as vapor deposition, sputtering, ALD (Atomic Layer Deposition), and CVD (Chemical Vapor Deposition). It is difficult to reduce the cost in terms of production efficiency, and it is difficult to apply it to large areas.

  Thus, electrodeposition methods, screen printing methods, spray pyrolysis methods, and the like can be cited as film forming methods that are inexpensive and capable of increasing the area without relying on a vacuum process. A CdTe solar cell is produced as a solar cell manufactured by such a high-speed and low-cost process. The CdTe solar cell by this method has a conversion efficiency of 10% in the module, which is very low compared with the conversion efficiency of about 15%, which is the conversion efficiency of other solar cell modules. This is because the cost is 100 yen / W or less, which is about two-fifths of other solar cells. In other words, it turned out that the biggest concern of consumers is cost. Therefore, it is clear that the cost aspect is a very important factor in production and sales.

  From the above, the most important point in the production of solar cells is the cost. From this viewpoint, the spray pyrolysis method is promising. The spray pyrolysis method is known as a film formation method for a large area, and is an attractive film formation method that can greatly reduce the power generation cost if it can be applied to at least one film formation process for CIS solar cell production. Sufficient photoelectric conversion efficiency and reproducibility are important for commercial production of CIS solar cells by spray pyrolysis.

  An object of this invention is to provide the photoelectric conversion element which consists of a CIS solar cell which can be manufactured at low cost, and has improved the solar cell characteristic, and its manufacturing method.

In view of the above-mentioned purpose, as a result of intensive research on a method for improving the characteristics of a solar cell by improving its characteristics, a buffer layer generally used in CIS solar cells is formed by a spray method. It was found that the solar cell characteristics can be improved by forming a buffer layer made of In ₂ S ₃ to which other materials are added by spraying, and the present invention has been made. That is, the present invention has the following configuration.

The present invention relates to a photoelectric conversion of a CIS solar cell including a metal oxide semiconductor layer, a buffer layer stacked in contact with the metal oxide semiconductor layer, and a light absorption layer stacked in contact with the buffer layer on the side opposite to the metal oxide semiconductor layer. In particular, the buffer layer is composed of an In ₂ S ₃ layer to which other materials are added. From the viewpoint of production cost, the buffer layer is preferably formed by spraying in air.

  Examples of other materials added to the buffer layer include titanium (Ti), zinc (Zn), tin (Sn), niobium (Nb), yttrium (Y), lanthanum (La), zirconium (Zr), and tantalum. (Ta), hafnium (Hf), strontium (Sr), barium (Ba), calcium (Ca), vanadium (V), metal containing at least one selected from the group consisting of tungsten (W), etc. Is preferred.

Examples of the buffer layer to which other materials are added include CdS. In addition to safety concerns, In ₂ S ₃ is preferable because light absorption shows a decrease in the spectral response in the blue region.

  The thickness of the other material addition buffer layer is about 0.1 to 1.0 μm, preferably about 0.2 to 0.8 μm. The buffer layer added with the other material having such a thickness becomes a high-resistance n-type semiconductor layer having an effect of improving reproducibility.

The metal oxide semiconductor used for the metal oxide semiconductor layer is not particularly limited as long as it is an n-type semiconductor having a band gap of about 2 to 5 eV. For example, titanium (Ti), zinc (Zn), tin (Sn), niobium (Nb), indium (In), yttrium (Y), lanthanum (La), zirconium (Zr), tantalum (Ta), hafnium (Hf) ), Strontium (Sr), barium (Ba), calcium (Ca), vanadium (V), a metal oxide containing at least one selected from the group consisting of metal elements such as tungsten (W) is preferable. Further, it contains at least one selected from the group consisting of non-metallic elements such as nitrogen (N), carbon (C), fluorine (F), sulfur (S), chlorine (Cl), and phosphorus (P). May be. In particular, an n-type semiconductor whose conduction band is lower in the electron energy level than the conduction band of the buffer In ₂ S ₃ layer to which other materials are added is preferable. Specifically, titanium oxide, tungsten oxide, zinc oxide, niobium oxide, tantalum oxide, strontium titanate, and the like are more preferable, and titanium oxide is more preferable. Note that in the case where a perovskite oxide semiconductor is used as the metal oxide semiconductor, a donor may be doped. By forming a metal oxide semiconductor layer made of these metal oxide semiconductors, the metal oxide semiconductor layer becomes a window layer for introducing light into a light absorption layer described later, and another material addition buffer described later It can be an n-type semiconductor layer that plays a role of collecting electrons from the layer. In addition, these metal oxide semiconductors may be used independently and may be used in combination of 2 or more type.

  When titanium oxide is employed as the metal oxide semiconductor used for the metal oxide semiconductor layer, it is preferable to use an anatase type crystal structure.

  The thickness of the metal oxide semiconductor layer is preferably about 10 to 2000 nm, and more preferably about 20 to 300 nm. By setting the thickness of the metal oxide semiconductor layer to this level, it is possible to more reliably suppress the leakage current and collect electrons from the other material addition buffer layer described later.

The light absorption layer is preferably made of a chalcopyrite semiconductor. Examples of the chalcopyrite semiconductor that can be used for the light absorption layer include CuInS ₂ , CuIn (S, Se) ₂ , and CuZnSnS ₂ .

  The light absorption layer is preferably formed by a spray method. Thereby, since a vacuum process is not used, manufacturing cost can be reduced.

  The thickness of the light absorption layer can be made thinner than that of the dye-sensitized solar cell, preferably about 0.8 to 3.0 μm, more preferably about 1.0 to 2.5 μm.

  A light-transmitting conductive layer is preferably provided on the side opposite to the other material-added buffer layer in contact with the metal oxide semiconductor layer. The light-transmitting conductive layer may be made of, for example, a transparent conductive oxide. For example, fluorine-doped tin oxide (FTO), indium tin oxide (ITO), gallium-doped zinc oxide, aluminum-doped zinc What consists of an oxide, niobium dope titanium oxide, etc. is preferable, and what consists of ITO among these is more preferable. Thereby, a translucent conductive layer becomes a window layer for introducing into a light absorption layer, and the electric power obtained from the light absorption layer can be taken out efficiently.

  The thickness of the translucent conductive layer is preferably about 0.1 to 10.0 μm, and more preferably about 0.3 to 1.0 μm. By setting the thickness of the translucent conductive layer within the above range, the sheet resistance can be reduced, and as a result, the series resistance of the photoelectric conversion device can be reduced, so that the fill factor characteristic can be maintained.

  A light-transmitting substrate is preferably provided on the side opposite to the metal oxide semiconductor layer in contact with the light-transmitting conductive layer. Although it does not restrict | limit especially as a translucent board | substrate, For example, what is necessary is just to comprise from glass, a plastics, etc. Thereby, it can become a window layer for introducing light into the light absorption layer. Although the thickness of a translucent board | substrate is not specifically limited, What is necessary is just to be about 0.1-5.0 mm.

  For example, a substrate with a transparent conductive film such as a glass with an ITO film or a glass with an FTO film may be used as the light-transmitting substrate and the light-transmitting conductive layer.

  A back electrode is preferably provided on the side opposite to the other material-added buffer layer in contact with the light absorption layer. Although it does not restrict | limit especially as a back electrode, For example, a metal electrode, especially molybdenum, gold | metal | money, silver, aluminum, carbon, platinum etc. are preferable. Also, alloys of these metals are preferably used. The thickness of the back electrode is not particularly limited, but may be about 0.1 to 2.0 μm.

  In the present invention, the terms “translucent” or “transparent” mean that the light absorption layer transmits light of at least a part of the wavelength range in which the photoelectric conversion function is exhibited. That is, it means that it is transparent to ultraviolet, visible or near infrared wavelength light.

The production method of the present invention relating to the production of a photoelectric conversion element is characterized in that the buffer layer constituting the photoelectric conversion element of the present invention is formed by a spray method. That is, the buffer layer is a metal oxide semiconductor in which a precursor solution made of a constituent material compound of In ₂ S ₃ added with other materials is heated in the state where the surface of the metal oxide semiconductor layer as a base is heated to 150 to 400 ° C. It is formed by spraying on the surface of the layer.

  In a preferred embodiment, the metal oxide semiconductor layer and the light absorption layer are also formed by a spray method. That is, in a state where the surface on which the metal oxide semiconductor layer and the light absorption layer are to be formed is heated to a predetermined temperature, the precursor solution composed of each constituent raw material compound is placed on the surface of each substrate in the air. Formed by spraying. Thus, as the number of steps formed by the spray method is increased, the manufacturing cost is reduced.

The photoelectric conversion element of this invention can improve a solar cell characteristic by adding another material to the buffer layer.
In the photoelectric conversion element manufacturing method of the present invention, the production cost can be reduced by forming the buffer layer by a spray method as compared with the case of using a vacuum process.

It is a schematic cross section which shows one aspect | mode of the photoelectric conversion element of this invention which has another material addition buffer layer.

  Specific embodiments of the photoelectric conversion element of the present invention described above will be described in more detail with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view illustrating one embodiment of the photoelectric conversion element of the present invention when the metal oxide semiconductor layer has a smooth structure.

  This photoelectric conversion element can be formed with, for example, a superstrate structure, and a translucent substrate 2 is disposed on the lower surface side as one main surface, on which a translucent conductive layer 3 and a metal oxide semiconductor are disposed. The layer 4, the other material addition buffer layer 5, the light absorption layer 6, and the back electrode 7 are laminated in this order. By adopting such a configuration, high photoelectric conversion efficiency can be realized with high reproducibility.

  In the present invention, “upper” and “lower” are merely displayed based on the drawings for the sake of convenience, and have no special meaning. Depending on the arrangement direction of the element, it may be upside down or left and right.

  The materials and thicknesses of the translucent substrate 2, the translucent conductive layer 3, the metal oxide semiconductor layer 4, the other material added buffer layer 5, the light absorption layer 6 and the back electrode 7 are as described above.

  The translucent conductive layer 3 may be formed on the translucent substrate 2 by a CVD method, a sputtering method, a spray method, or the like. The spray method is preferable in consideration of manufacturing cost, easy area enlargement, and stable quality. Commercially available glass with a transparent conductive film or the like can also be used as the translucent substrate 2 and the translucent conductive layer 3.

  The metal oxide semiconductor layer 4 may be formed on the translucent conductive layer 3 by a CVD method, a sputtering method, a spray method, or the like. The spray method is preferable in consideration of manufacturing cost, easy area enlargement, and stable quality.

The other material addition buffer layer 5 is formed on the metal oxide semiconductor layer 4 by a spray method. For example, on the surface of the metal oxide semiconductor layer 4 whose surface is heated to 150 to 400 ° C., a raw material solution containing InCl ₃ , CS (NH ₂ ) ₂ and TiCl ₄ which is another material (concentration is InCl, respectively) ₃ : 1 mM to 500 mM, CS (NH ₂ ) ₂ : 1 mM to 500 mM, and TiCl _{4 1} mM to 500 mM) may be sprayed in the air to form the other material added buffer layer. At this time, if the surface temperature of the metal oxide semiconductor layer 4 is too low, sufficient thermal decomposition reaction of the sprayed raw material compound for the other material added buffer layer cannot be obtained, and the desired other material added buffer layer is obtained. I can't. If the surface temperature of the metal oxide semiconductor layer 4 is too high, it is difficult to increase the thickness of the other material addition buffer layer 5.

The light absorption layer 6 is formed on the other material addition buffer layer 5 by a spray method. For example, a raw material solution containing CuCl ₂ , InCl ₃ and CS (NH ₂ ) ₂ on the surface of the other material addition buffer layer 5 whose surface is heated to 250 to 400 ° C., preferably 280 to 375 ° C. (concentration is CuCl ₂ : 1 mM to 500 mM, InCl ₃ : 1 mM to 500 mM, and CS (NH ₂ ) ₂ : 1 mM to 1000 mM) may be sprayed in the air to form the light absorption layer 6. At this time, if the surface temperature of the other material-added buffer layer 5 is too low, sufficient thermal decomposition reaction of the sprayed raw material compound for the light absorption layer cannot be obtained. Moreover, the photoelectric conversion efficiency of the other material addition buffer layer 5 is remarkably deteriorated. The CuCl ₂ used may be a hydrate (CuCl ₂ .2H ₂ O), and the CS (NH ₂ ) ₂ may be CS (NHCH ₃ ) ₂ . In addition, although the example was shown about the other material addition buffer layer 5 and the light absorption layer 6 above, it is not limited to this, It can produce with various composition and conditions.

The back electrode 7 may be formed on the light absorption layer 6 by vapor deposition, CVD, sputtering, screen printing, or the like.
(Use of photoelectric conversion elements)

  The photoelectric conversion element of the present invention can be applied to various uses by using the photoelectric conversion element as a power generation means and supplying the generated power to a load. Specifically, the photoelectric conversion device of the present invention, a photoelectric conversion device having a configuration including an inverter device that converts a direct current output from the photoelectric conversion device of the present invention into an alternating current, an electric motor, a lighting device, and the like can do. As its application, for example, it can be used as a CIS type solar cell installed on the roof, wall surface, etc. of a building.

  The present invention will be described more specifically based on examples, but the present invention is not limited to these examples.

(Example)
The photoelectric conversion element of the aspect of FIG. 1 was produced as follows. As the translucent substrate 2 having the translucent conductive layer 3, a translucent conductive layer composed of a SnO ₂ : F layer (fluorine-doped SnO ₂ layer) having a sheet resistance of 10 Ω / □ (square) and a thickness of about 0.5 μm. Was prepared on one main surface (surface area was 25 cm ² ), and a metal oxide semiconductor layer 4 made of titanium oxide was laminated thereon to a thickness of about 100 nm. The spraying method is used as the laminating method, the surface temperature of the translucent conductive layer 3 is set to about 400 to 450 ° C., and the precursor solution is a TAA solution (titanium (IV) isopropoxide and acetylacetone = 1: 2 (molar ratio)). Using an ethanol solution diluted 10 times, the solution was sprayed for 10 minutes at a spray rate of 1 ml / min. As a spraying method, a glass sprayer according to Venturi's law was used, and the distance from the substrate was set to about 20 cm.

On this metal oxide semiconductor layer 4, another material addition buffer layer 5 having a film thickness of about 0.2 μm was formed by spraying. The surface temperature of the metal oxide semiconductor layer 4 was set to about 300 ° C., and 30 ml of an aqueous solution in which 10 mM InCl ₃ , 30 mM CS (NH ₂ ) ₂ and 0.8 mM TiCl ₄ were mixed as a precursor solution was sprayed for 20 minutes. . As a spraying method, an automatic spray gun (HMP-6RWX type manufactured by Lumina) was used, and the distance from the substrate was set to about 30 cm.

Next, about 1 μm of the light absorption layer 6 was laminated on the other material added buffer layer 5 by a spray method. At this time, the surface temperature of the other material addition buffer layer 5 is set to about 300 ° C., and the precursor solution is an aqueous solution in which 30 mM CuCl ₂ .2H ₂ O, 30 mM InCl ₃ and 150 mM CS (NH ₂ ) ₂ are mixed. 40 ml was used and sprayed for 30 minutes. As a spraying method, an automatic spray gun (HMP-6RWX type manufactured by Lumina) was used, and the distance from the substrate was set to about 30 cm.

  Finally, gold was deposited as a back electrode 7 on the light absorption layer 6 by a vapor deposition method to a thickness of 50 nm to produce a photoelectric conversion element.

The size of the photoelectric conversion element is about 5 mm square (= 25 mm ² ), and in order to form a plurality of photoelectric conversion elements on one glass substrate, the metal oxide semiconductor layer 4, the buffer layer 5, and the light absorption layer 6 are formed. And when forming the back electrode 7, it sprayed or vapor-deposited on the translucent conductive layer 3 of a glass substrate, and piled up the metal mask board in which several square holes with a side of 5 mm were made. In the resulting photoelectric conversion element, as shown in FIG. 1, in order to partially expose the light absorption layer 6 from the back electrode 7, the area of the hole is used as a mask plate for forming the back electrode 7. A material slightly smaller than the area of the light absorption layer 6 may be used. The material of the mask plate is stainless steel, for example, and is not particularly limited as long as it is not affected by the substrate temperature.

(Comparative example)
The photoelectric conversion element which produced the photoelectric conversion element like the Example except having used the buffer layer without addition of other materials was used as a comparative example.

Specifically, without adding 0.8 mM TiCl ₄ to the precursor solution of the buffer layer without addition of other materials, a mixed aqueous solution of 10 mM InCl ₃ and 30 mM CS (NH ₂ ) ₂ was used as in the examples. 30 ml was used and sprayed for 20 minutes to form a buffer layer.

(Test results)
About the photoelectric exchange element of an Example and a comparative example, the light (100 mW / cm < ² >) of the solar simulator of AM1.5 was irradiated, and the photoelectric characteristic was measured at room temperature (for example, 20 degreeC).

The photoelectric conversion element of the comparative example had an open circuit voltage, a fill factor, and a photoelectric conversion efficiency of 0.52 V, 0.42, and 2.1%, respectively. On the other hand, in the photoelectric conversion element of the Example which laminated | stacked the other material addition buffer layer, the result was 0.55V, 0.47, and 2.2%, respectively. Comparing these photoelectric conversion elements, the addition of another material Ti to the buffer In ₂ S ₃ layer increases the open-circuit voltage and the fill factor, thereby improving the photoelectric conversion efficiency.

DESCRIPTION OF SYMBOLS 1 Photoelectric conversion element 2 Translucent board | substrate 3 Translucent conductive layer 4 Metal oxide semiconductor layer 5 Other material addition buffer layer 6 Light absorption layer 7 Back electrode S Sunlight

Claims (10)

A metal oxide semiconductor layer;
A buffer layer stacked in contact with the metal oxide semiconductor layer, wherein the buffer layer includes titanium (Ti), zinc (Zn), tin (Sn), niobium (Nb), yttrium (Y), lanthanum (La ), Zirconium (Zr), tantalum (Ta), hafnium (Hf), strontium (Sr), barium (Ba), calcium (Ca), vanadium (V), and tungsten (W). made of metal from an in ₂ S ₃ with the addition of a buffer layer as other materials added an in ₂ S ₃ layer formed by spraying in air,
A light absorption layer laminated on the opposite side of the metal oxide semiconductor layer in contact with the buffer layer;
A photoelectric conversion element comprising:   2. The photoelectric device according to claim 1, wherein the metal oxide semiconductor layer is at least one selected from the group consisting of titanium oxide, tungsten oxide, zinc oxide, niobium oxide, tantalum oxide, and strontium titanate. Conversion element.   The photoelectric conversion element according to claim 1, wherein the light absorption layer is made of a chalcopyrite semiconductor.   The photoelectric conversion element according to claim 1, further comprising a light-transmitting conductive layer on a side opposite to the buffer layer in contact with the metal oxide semiconductor layer.   The translucent conductive layer is at least one transparent conductive material selected from the group consisting of fluorine-doped tin oxide, indium-doped tin oxide, gallium-doped tin oxide, aluminum-doped tin oxide, and niobium-doped tin oxide. It is an oxide, The photoelectric conversion element as described in any one of Claim 1 to 4. Further comprising a translucent substrate in contact with the translucent conductive layer on the side opposite to the metal oxide semiconductor layer,
The photoelectric conversion element according to any one of claims 1 to 5, further comprising a back electrode on a side opposite to the buffer layer in contact with the light absorption layer.   The photoelectric conversion element according to claim 6, wherein the translucent substrate is made of glass or plastic.   The photoelectric conversion element according to claim 6 or 7, wherein the back electrode is made of at least one selected from the group consisting of molybdenum, gold, silver, aluminum, carbon, and platinum. A method for producing the photoelectric conversion device according to claim 1,
In the formation of the buffer layer, a precursor solution made of the constituent material compound of the other material added In ₂ S ₃ is heated in the air while the surface of the metal oxide semiconductor layer as a base is heated to 150 to 400 ° C. A method for producing a photoelectric conversion element, comprising spraying the surface of an oxide semiconductor layer.   Each of the metal oxide semiconductor layer and the light absorption layer is heated on the surface on which the base material is formed at a predetermined temperature, and a precursor solution made of each constituent raw material compound is placed on the base surface in the air. The method for producing a photoelectric conversion element according to claim 9, wherein the photoelectric conversion element is formed by spraying on the surface.

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