TW201427054A - Photoelectric conversion element and method of producing the same, manufacturing method for buffer layer of photoelectric conversion element, and solar cell - Google Patents

Abstract

The present invention provides a photoelectric conversion element having a buffer layer which suppresses characteristics variation among elements. The photoelectric conversion element has a bottom electrode layer 20, a photoelectric conversion layer 30, a buffer layer 40, and a translucent conductive layer 60 laminated on a substrate 10, wherein the photoelectric conversion layer contains a compound semiconductor of a chalcopyrite structure of at least one of group Ib element, group IIIb element and group VIb element as a main component. The buffer layer 40 comprises a compound with an alkali metal, which is at least one of lithium, sodium, and potassium. A content of the alkali metal in the compound forming the buffer layer is 0.1at% to 5at%.

Description

Method for manufacturing buffer layer of photoelectric conversion element and photoelectric conversion element

The present invention relates to a method of manufacturing a buffer layer for a photoelectric conversion element and a photoelectric conversion element of a solar cell, a CCD (Solid State Sensor) sensor, and the like, and a method of manufacturing the photoelectric conversion element.

A photoelectric conversion element including a photoelectric conversion layer and an electrode that is electrically connected thereto is used for applications such as solar cells. In the past, in solar cells, monocrystalline germanium or polycrystalline germanium in bulk, or amorphous germanium solar cells in thin films have been the mainstream. Research and development of compound semiconductor solar cells that do not rely on bismuth have been ongoing. In a compound semiconductor-based solar cell, a bulk system such as GaAs (gallium arsenide) or a CIS (copper indium selenide) or CIGS (copper indium gallium selenide) containing a group Ib element and a group IIIb element and a group VIb element Film systems such as those are well known. CI(G)S is a compound represented by the general formula Cu _1-z In _1-x Ga _x Se _2-y S _y (wherein, 0≦x≦1, 0≦y≦2, 0≦z≦1) The semiconductor is a CIS system when x=0, and a CIGS system when x>0. In the present specification, CIS and CIGS are combined and described as "CI(G)S".

In a conventional thin film photoelectric conversion element such as CI (G)S system, generally, CdS (vulcanization) is provided between the photoelectric conversion layer and the light-transmitting conductive layer formed thereon. Cadmium) buffer layer. In such a system, the buffer layer is usually formed into a film by a chemical bath deposition method (CBD method: Chemical Bath Deposition).

In recent years, the Cd free of the buffer layer has been studied in consideration of the environmental load. A zinc-based compound such as Zn(S, O) which is a main component of the Cd-free buffer layer is studied.

Patent Document 1 and Patent Document 2 propose a method of manufacturing a photoelectric conversion element including a Zn (S, O) based buffer layer.

[First technical literature]

[Patent Literature]

[Patent Document 1] JP-A-2011-119764

[Patent Document 2] JP-A-2012-18953

However, it has been clarified by the inventors of the present invention that the photoelectric conversion efficiency of a solar cell obtained by integrating a CIGS photoelectric conversion element to which a conventional Zn-based compound buffer layer is applied is seen from a single cell. Expected to be lower. The present inventors have found that a photoelectric conversion element including a buffer layer containing a Zn-based compound has a very large variation in characteristics between cells, and therefore, for a large-area solar cell (for example, a plurality of single cell cells) The sub-modules are connected in series, and the characteristics are affected by the battery cells with lower efficiency, and the expected performance cannot be exhibited.

Compared with the Cds-based buffer layer, the uniformity of the Zn-based compound buffer layer is low, and therefore it is considered that the variation between the cell cells is relatively large. Therefore, when developing a photoelectric conversion element including a buffer layer of a Zn-based compound, it is important to reduce the variation in characteristics between the cells while improving the photoelectric conversion efficiency. And, preferably, the battery cell The difference in characteristics between the two is not limited to the Zn-based compound buffer layer, and is also the same in the case of a buffer layer containing a compound of any composition.

In view of the above circumstances, an object of the present invention is to provide a photoelectric conversion element including a buffer layer capable of suppressing variations in characteristics between elements.

Further, an object of the present invention is to provide a method for producing a buffer layer which can suppress variation in characteristics of an element, and to further provide a method for producing a photoelectric conversion element to which the method for producing a buffer layer is applied.

The photoelectric conversion element of the present invention is a photoelectric conversion element in which a bottom electrode layer, a photoelectric conversion layer, a buffer layer, and a light-transmitting conductive layer are laminated on a substrate, and the photoelectric conversion layer contains an Ib group element, a Group IIIb element, and VIb. a compound semiconductor of a chalcopyrite structure of at least one of the group elements as a main component, wherein the buffer layer comprises an alkali metal-containing compound, and the alkali metal is at least one of lithium, sodium and potassium, among the above compounds The content of the alkali metal is 0.1 at% or more and 5 at% or less.

The compound constituting the buffer layer preferably contains a metal, sulfur and oxygen. The metal is at least one selected from the group consisting of Cd, Zn, In, and Sn.

Further, the above metal is any one of Zn, In and Sn, and particularly Zn is preferable.

The content of the alkali metal is preferably 0.5 at% or more and 2.5 at% or less.

The thickness of the buffer layer is preferably 1 nm or more and 100 nm or less.

Preferably, the Group Ib element is at least one selected from the group consisting of Cu and Ag, and the Group IIIb element is at least one selected from the group consisting of Al, Ga, and In, and the Group VIb element is selected. At least one of the group consisting of S, Se, and Te.

The solar cell of the present invention is characterized in that a plurality of photoelectric conversion elements of the present invention are integrated.

The method for producing a buffer layer according to the present invention is a method for producing a buffer layer in which a bottom electrode layer, a photoelectric conversion layer, a buffer layer, and a light-transmitting conductive layer of a photoelectric conversion element are laminated on a substrate, and the photoelectric conversion layer is included A compound semiconductor of a chalcopyrite structure of at least one of a group Ib element, a group IIIb element and a group VIb element as a main component, wherein a chemical bath deposition containing a predetermined metal ion, thiourea, or an alkali metal ion of 1 M or more is prepared. In the reaction liquid to be used, at least the surface of the photoelectric conversion layer of the buffer film formation substrate in which the bottom electrode layer and the photoelectric conversion layer are laminated in this order is brought into contact with the reaction liquid, thereby depositing on the surface of the photoelectric conversion layer. The buffer layer.

The predetermined metal is preferably at least one of Cd, Zn, In, and Sn, and Zn, In, or Sn is more preferable, and Zn is particularly preferable.

In the case of an alkali metal, at least one of sodium, potassium and lithium is preferred.

A method for producing a photoelectric conversion element according to the present invention is a method for producing a photoelectric conversion element in which a bottom electrode layer, a photoelectric conversion layer, a buffer layer, and a light-transmitting conductive layer are laminated on a substrate, wherein the photoelectric conversion layer contains an Ib element , IIIb elements and a compound semiconductor of a chalcopyrite structure of at least one of the group VIb elements as a main component, It is characterized in that a buffer layer is formed by the method for producing a buffer layer of the present invention.

In the photoelectric conversion element of the present invention, a buffer layer is provided on a photoelectric conversion layer containing a compound semiconductor having a chalcopyrite structure as a main component, and the buffer layer has sodium, potassium and/or lithium in a ratio of 0.1 at% or more and 5 at% or less. The alkali metal compound is therefore excellent in in-plane uniformity of properties. An element having a buffer layer containing an alkali metal in an amount of 0.1 at% or more and 5 at% or less has a small variation in characteristics between the photoelectric conversion elements formed on the same substrate, and a photoelectric conversion element having uniform characteristics can be obtained.

Since the buffer layer contains an alkali metal and the buffer layer can be used as an alkali metal supply layer for the photoelectric conversion layer, photoelectric conversion can be obtained by adding an alkali metal to the photoelectric conversion layer without increasing the number of processes. The effect of increased efficiency.

In the solar cell of the present invention, since the photoelectric conversion element having high uniformity can be provided, it is possible to suppress the photoelectric conversion efficiency caused by the influence of the element having poor characteristics due to the problem that the uniformity between the photoelectric conversion elements is low. When it is low, a high photoelectric conversion efficiency can be obtained.

1‧‧‧ photoelectric conversion components

2‧‧‧Solar battery

10‧‧‧Substrate

11‧‧‧Al substrate

12‧‧‧Anodized film

20‧‧‧ bottom electrode layer

30‧‧‧ photoelectric conversion layer

40‧‧‧buffer layer

60‧‧‧Translucent conductive layer

61‧‧‧dick

62‧‧‧dick

64‧‧‧dick

70‧‧‧ Grid

Fig. 1 is a schematic cross-sectional view showing a layer structure of a photoelectric conversion element according to an embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view showing an example of an anodized substrate which can be applied to the photoelectric conversion element of the present invention.

Fig. 3 is a schematic plan view showing an integrated solar cell according to an embodiment of the present invention; Figure.

4 is a partially enlarged cross-sectional view showing an integrated solar cell.

Fig. 5 is a graph showing the results of composition analysis in the depth direction of the sample of Example 3.

Hereinafter, embodiments of the present invention will be described in detail.

A structure and a manufacturing method of a photoelectric conversion element according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of a photoelectric conversion element 1. In order to make it easier to recognize, the proportion of each component in the figure is appropriately changed from the actual object.

The photoelectric conversion element 1 has a bottom electrode layer (back electrode) 20, a photoelectric conversion layer 30, a buffer layer 40, and a light-transmitting conductive layer (transparent electrode) 60 and a gate as an upper electrode layer, which are sequentially laminated on the substrate 10. An element made up of a grid electrode 70. The photoelectric conversion layer 30 has a compound semiconductor containing a chalcopyrite structure of at least one of a group Ib element, a group IIIb element, and a group VIb element as a main component, and the buffer layer 40 includes an alkali metal content of 0.1 at% or more and 5 at A compound having a ratio of at least 100%, the alkali metal being at least one of lithium, sodium, and potassium.

Further, a so-called window layer may be provided between the buffer layer 40 and the light-transmitting conductive layer 60.

The buffer layer 40 is a layer provided for the purpose of preventing recombination of photo-generated carriers, integration of band discontinuities, lattice matching, and coverage of surface irregularities of the photoelectric conversion layer. Further, the damage of the light-transmitting conductive layer 60 at the time of film formation is moderated.

In the present embodiment, the compound constituting the buffer layer 40 is a compound containing a metal, sulfur, and oxygen. The metal (which may also have unavoidable impurities) is at least one selected from the group consisting of Cd, Zn, In, and Sn. When the metal is Zn, In or Sn, it is more effective. In particular, when the metal is Zn, that is, when the buffer layer 40 is a Zn-based compound, the effect of the present invention is particularly large.

When the metal is Zn, the main component constituting the buffer layer 40 is Zn(S, O) or Zn(S, O, OH). The description of Zn(S,O) and Zn(S,O,OH) can be explained as the mixed crystal of zinc sulfide and zinc oxide and the mixed crystal of zinc sulfide and zinc oxide and zinc hydroxide. A part of zinc sulfide or zinc oxide or zinc hydroxide exists in the form of amorphous or the like without forming a mixed crystal. In this case, the alkali metal contained in the buffer layer 40 can be interpreted as a buffer layer 40 composed of a compound formed by adding an alkali metal element to each of the main components Zn(S, O) and Zn(S, O, OH). . Further, when the metal is Cd, In, or Sn, a compound in which Zn of the above chemical formula is substituted with each of Cd, In, and Sn is obtained.

Further, the content of the alkali metal in the compound constituting the buffer layer 40 is 0.1 at% or more and 5 at% or less. The present inventors have found that (in the following embodiments), when it is contained in an amount of 0.1 at% or more, the in-plane uniformity of the buffer layer is improved, and the variation in characteristics of the photoelectric conversion element having such a buffer layer between cells is changed. Very small. Further, in the film formation of the buffer layer by the CBD method, it is difficult to add an alkali metal exceeding 5 at% to the buffer layer. Further, the content of the alkali metal in the buffer layer is preferably 0.5 at% or more and 2.5 at% or less.

Further, the compound constituting the buffer layer may contain two or more kinds of alkali metals. In the case of containing two or more alkali metals, the total content is 0.1 at% The above is 5 at% or less, and more preferably, the content is 0.5 at% or more and 1.5 at% or less.

The composition of the buffer layer can be determined, for example, by X-ray photoelectron spectroscopy (XPS) measurement, and the content of the alkali metal can be determined by measuring the result.

The mechanism of action for reducing the variation in photoelectric conversion efficiency between elements by containing an alkali metal in the buffer layer is not known at present, but it is considered that the energy band structure of the buffer layer is changed by the presence of an alkali metal, and An effect of suppressing recombination of carriers occurring in the photoelectric conversion layer is produced.

Further, by supplying the alkali metal to the buffer layer and supplying the alkali metal for the photoelectric conversion layer containing the CIGS layer, it is also expected to improve the characteristics of the photoelectric conversion layer. It has been conventionally known to improve the photoelectric conversion efficiency by adding an alkali metal to the CIGS layer. As a method of adding an alkali metal for CIGS, a glass substrate using an alkali metal-containing soda-lime glass or a substrate provided with an alkali metal supply layer is known, and a film is formed in CIGS. A technique of adding an alkali metal to CIGS at the time of thermal diffusion from a substrate (JP-A-2011-233874); or forming an alkali metal-containing compound on the surface of CIGS after film formation of a CIGS precursor A technique of forming an alkali metal-containing CIGS by heat treatment (International Publication No. 2005/109525). In the method other than the glass substrate using a soda-lime glass or the like containing an alkali metal in advance, a process of increasing the supply of the alkali metal for the CIGS layer is generated. In the present invention, since the buffer layer containing an alkali metal is formed into a film, the buffer layer can function as an alkali metal supply layer for the CIGS layer. That is, after the buffer layer is formed into a film, the alkali metal is directed to the CIGS by heat treatment at an appropriate temperature. Layer diffusion allows for improved photoelectric conversion efficiency.

The thickness of the buffer layer 40 is 1 nm or more and 1 μm or less, preferably 1 nm or more and 10 nm or less, and more preferably 5 nm or more, particularly preferably 10 nm or more.

Further, the buffer layer 40 preferably has a crystalline portion and an amorphous portion. The molar number of the sulfur atom and the oxygen atom in the buffer layer 40 is preferably 0.2 to 0.8 in terms of the molar number of the sulfur atom. The molar ratio is preferably from 0.4 to 0.5.

Further, the conductivity type of the buffer layer 40 is not particularly limited, and an n-type is particularly preferable.

Hereinafter, a method of manufacturing the buffer layer 40 will be described. In addition, the compound may contain unavoidable impurities.

<film formation step>

The film formation of the buffer layer is by the CBD method.

The so-called "CBD" method, such as the general formula "M(L) _i " ^m+ M ⁿ +iL means (wherein M: metal element, L: ligand, m, n, i: each represents a positive number.) means that by balancing and achieving supersaturation conditions, in a stable environment, appropriate Speed, a method of depositing crystals on a substrate.

In the reaction liquid used for chemical bath deposition, a predetermined metal ion, thiourea, or an alkali metal ion of 1 M or more is used. Hereinafter, a preferred composition of the reaction liquid for chemical bath deposition will be described. In the following, the case where the set metal is zinc will be described, and the case of cadmium, indium, and tin is also substantially the same.

As a source of zinc, it is preferably selected from the group consisting of zinc sulfate, zinc acetate, and nitrate. At least one of the group consisting of zinc acid, zinc citrate, and hydrates of these. The concentration is not particularly limited, and is preferably 0.001 to 0.5 M.

The concentration of thiourea is not particularly limited, and is preferably 0.01 to 1.0 M.

Further, it contains 1 M or more of an alkali metal ion. Here, as a source of the alkali metal, it is preferred to contain trisodium citrate, tripotassium citrate, trilithium citrate, and/or a hydrate thereof. Sodium is used when trisodium citrate is used, potassium is used when tripotassium citrate is used, and lithium is used when trilithium citrate is used, and is incorporated into the buffer layer.

Further, the trisodium citrate, tripotassium citrate, and trilithium citrate have a function as a correcting agent, and are added to the reaction liquid at the time of formation of the buffer layer by a conventional chemical bath deposition method. For example, Patent Document 1 discloses that the concentration of trisodium citrate in the reaction liquid is preferably 0.001 to 0.25 M. In the present invention, the concentration of the alkali metal ion in the reaction liquid is set to 1 M or more, and therefore the concentration of trisodium citrate is 0.34 M or more. In order to have a sufficient alkali metal in the buffer layer, such a concentration is necessary. In the preferred concentration range of the conventional trisodium citrate, the concentration of sodium ions is as large as 0.75 M, and it is difficult to obtain a buffer layer having a sodium content of 0.1 at% or more.

Further, the reaction liquid preferably contains an ammonium salt such as NH ₄ OH which functions as a pH control chemical. The ammonium salt can also be used as a component of a function such as a correcting agent. The concentration of the ammonium salt is preferably from 0.001 to 0.40 M. By adjusting the pH in this way, the solubility and supersaturation of the metal ions can be adjusted. If the concentration of the ammonium salt is in the range of 0.001 to 0.40 M, the reaction rate is fast, and even if the step of forming the fine particle layer is not provided before the film forming step, film formation may be carried out at a practical production speed; the concentration of the ammonium salt exceeds At 0.40 M, the reaction rate becomes slow, and it is necessary to increase the particle layer or the like before the film formation step. The concentration of the ammonium salt is preferably from 0.01 to 0.03 M.

The pH of the reaction solution before the start of the reaction was set to 9.0 to 12.0.

When the pH of the reaction liquid before the start of the reaction is less than 9.0, the decomposition reaction of the component (S) such as thiourea is not performed, and even if it is carried out, it is extremely slow, so that the precipitation reaction does not proceed. The decomposition reaction of thiourea is as follows. The decomposition reaction of thiourea is described in Journal of Electrochemistry Society 141, 205-210 (1994) (Journal of the Electrochemical Society, 141, 205-210 (1994)) and Crystal Growth Journal 299, pp. 136-141. (2007) (Journal of Crystal Growth 299, 136-141 (2007)) and the like.

When the pH before the start of the reaction of the reaction liquid exceeds 12, the effect of the component (N), which is a function such as a distorting agent, is increased, and the precipitation reaction is not carried out, or it is extremely slow even if it is carried out. The pH of the reaction solution before the start of the reaction is preferably from 9.5 to 11.5.

In the reaction liquid to be used in the present invention, the concentration of the component (N) is set to be 0.001 to 0.40 M. If the concentration is such a concentration, the pH is adjusted to a specific value even without using a pH adjuster other than the component (N). Usually, the pH of the reaction liquid before the start of the reaction is set in the range of 9.0 to 12.0.

The pH of the reaction solution after completion of the reaction is not limited. Reaction solution The pH after completion of the reaction is preferably from 7.5 to 11.0. When the pH of the reaction liquid after the completion of the reaction is less than 7.5, it means that the reaction period is not included, and it is meaningless in consideration of efficient production. Further, in the case where the pH is still lowered even after the buffering ammonia is added to the system, there is a high possibility that ammonia is excessively volatilized in the heating step, and improvement in manufacturing is necessary. When the pH of the reaction liquid exceeds 11.0, the decomposition of thiourea is promoted. However, since most of the zinc ions are stabilized as an ammonia complex, the progress of the precipitation reaction is remarkably delayed. The pH of the reaction liquid after completion of the reaction is more preferably 9.5 to 10.5.

In the reaction liquid of the present invention, even if the pH adjusting agent other than the component (N) is not adjusted to a specific pH value, the pH of the reaction liquid after the start of the reaction is usually in the range of 7.5 to 11.0.

The reaction temperature is set to 70 ° C to 95 ° C. If the reaction temperature is less than 70 ° C, the reaction rate becomes slow, the film does not grow, or the film grows but it is difficult to obtain a desired thickness at a practical reaction rate. When the reaction temperature exceeds 95 ° C, the generation of bubbles or the like in the reaction liquid increases, and those bubbles or the like adhere to the surface of the film, and it is difficult to grow a flat and uniform film. Further, in the case where the reaction is carried out in an open system, stable concentration of film deposition conditions is difficult to maintain due to a change in concentration such as solvent evaporation. The reaction temperature is preferably from 80 ° C to 90 ° C.

The reaction time is not particularly limited. In the case of the present invention, the reaction can be carried out at a practical reaction rate even without providing a fine particle layer. The reaction time depends on the reaction temperature, for example, between 10 and 90 minutes, and has a good coating on the undercoat, and can be formed into a film to have a sufficient thickness to serve as a buffer layer. Floor.

The reaction liquid used in the present invention is an aqueous solution, and the pH of the reaction liquid is not a strongly acidic condition. Although the pH of the reaction solution may be from 11.0 to 12.0, the reaction may be carried out under mild pH conditions of less than 11.0, so that a hydroxide ion and a metal of a counter ion can be formed, and it is easy to use in an alkaline solvent. For example, when the substrate of the metal to be dissolved can be applied to an anodized substrate or the like as a flexible substrate, it is possible to form a buffer layer having high uniformity without causing damage to the substrate. The anodized substrate includes an anodized substrate on which an anodized film containing Al ₂ O ₃ as a main component is formed on at least one surface of an Al substrate containing Al as a main component; and Fe as a main component An anodized substrate in which an anodized film containing Al ₂ O ₃ as a main component is formed on at least one surface of a composite substrate of an Al material containing Al as a main component on at least one surface of the Fe material; An anodic oxide film containing Al ₂ O ₃ as a main component is formed on at least one surface of a substrate on which at least one surface of an Fe material containing Fe as a main component is formed on at least one surface of a Fe material containing Fe as a main component. Anodized substrate, etc.

Further, after the film formation step, at least the buffer layer is annealed at a temperature lower than the heat resistance temperature of the substrate. The temperature of the annealing treatment is set to 150 ° C or higher because an effect of improving the photoelectric conversion efficiency is obtained. The annealing treatment method is not particularly limited, and may be heating in a heating device or a dryer, or may be light annealing such as laser annealing or flash lamp annealing.

The photoelectric conversion element of the present invention has no structure other than the buffer layer. Do not limit it. Hereinafter, preferred examples of the respective constituent elements other than the buffer layer will be described in order.

(substrate)

The substrate 10 is not particularly limited, and a glass substrate, a metal substrate such as stainless steel on which an insulating film is formed on the surface, or a surface on at least one side of an Al substrate containing Al as a main component can be used. An anodized substrate having an anodized film containing Al ₂ O ₃ as a main component, and at least one surface of an Fe material containing Fe as a main component, at least a composite substrate of an Al material containing Al as a main component An anodized substrate having an anodized film containing Al ₂ O ₃ as a main component is formed on one surface thereof, and Al having Al as a main component is formed on at least one surface of a Fe material containing Fe as a main component. An anodized substrate of an anodized film containing Al ₂ O ₃ as a main component, a resin substrate such as polyimide, or the like is formed on at least one surface of the substrate of the film.

From the viewpoint of being able to be produced by a roll-to-roll process, a metal substrate, an anodized substrate, and a flexible substrate such as a resin substrate on which an insulating film is formed on the surface is preferable.

In view of the thermal expansion coefficient, the heat resistance, and the insulating properties of the substrate, the anodized substrate is particularly preferably formed of Al ₂ O ₃ on a surface selected from at least one side of an Al substrate having Al as a main component. An anodized substrate of an anodized film as a main component is formed on at least one surface of a composite substrate in which an Al material containing Al as a main component is compounded on at least one surface of a Fe material containing Fe as a main component. An anodized substrate having an anodized film containing Al ₂ O ₃ as a main component and a substrate on an Al film containing Al as a main component are formed on at least one surface of a Fe material containing Fe as a main component. A group of anodized substrates of an anodized film containing Al ₂ O ₃ as a main component is formed on at least one surface.

2 is a substrate on which the anodized film 12 is formed on both sides of the Al substrate 11, and the right side of FIG. 2 is a schematic view of a substrate on which an anodized film 12 is formed on one surface of the Al substrate 11. The anodized film 12 is made of Al ₂ O ₃ as a main component.

In the manufacturing process of the element, it is preferable to suppress the bending of the substrate caused by the difference in thermal expansion coefficient between Al and Al ₂ O ₃ and the film peeling caused thereby, as shown in the left diagram of FIG. A substrate on which the anodized film 12 is formed on both surfaces of the Al substrate 11.

Further, a layer of soda-lime glass (SLG) may be provided on the anodized film of the anodized substrate. By providing the soda lime glass layer, Na can be diffused to the photoelectric conversion layer 30, and the photoelectric conversion layer 30 contains Na, whereby the photoelectric conversion efficiency can be further improved.

Further, a soda lime glass layer may be provided on the substrate. By providing the soda lime glass layer, Na can be diffused to the photoelectric conversion layer 30, and the photoelectric conversion layer 30 contains Na, whereby the photoelectric conversion efficiency can be further improved.

(bottom electrode)

The main component of the bottom electrode (back surface electrode) 20 is not particularly limited, and Mo, Cr, W, and these are preferably combined, and particularly preferably Mo. The film thickness of the bottom electrode (back surface electrode) 20 is not limited, but is preferably about 200 to 1000 nm. For example, the bottom electrode 20 may be formed by sputtering on a substrate by a sputtering method.

(photoelectric conversion layer)

The main component of the photoelectric conversion layer 30 is not particularly limited, and from the viewpoint of obtaining high photoelectric conversion efficiency, at least one compound semiconductor of a chalcopyrite structure is preferable, and it is more preferable to contain an Ib element and At least one compound semiconductor of a group IIIb element and a group VIb element.

As a main component of the photoelectric conversion layer 30, a compound semiconductor containing at least one of a group Ib element, a group IIIb element, and a group VIb element is preferable. The above Group Ib element is selected from at least one of the group consisting of Cu and Ag. The above Group IIIb element is at least one selected from the group consisting of Al, Ga, and In. The above Group VIb element is selected from at least one of the group consisting of S, Se and Te.

As the compound semiconductor, e.g. _{CuAlS 2, CuGaS 2, CuInS 2} , CuAlSe 2, CuGaSe 2, AgAlS 2, AgGaS 2, AgInS 2, AgAlSe 2, AgGaSe 2, AgInSe 2, AgAlTe 2, AgGaTe 2, AgInTe 2, Cu ( In, Al)Se ₂ , Cu(In,Ga)(S,Se) ₂ , Cu _1-z In _1-x Ga _x Se _2-y S _y (wherein 0≦x≦1,0≦y≦ 2,0≦z≦1)(CI(G)S), Ag(In,Ga)Se ₂ and Ag(In,Ga)(S,Se) ₂ and the like.

Further, Cu ₂ ZnSnS ₄ , Cu ₂ ZnSnSe ₄ , Cu ₂ ZnSn(S, Se) ₄ or the like may be used.

The film thickness of the photoelectric conversion layer 30 is not particularly limited, but is preferably 1.0 to 4.0 μm, and particularly preferably 1.5 to 3.5 μm.

The film formation method of the photoelectric conversion layer 30 is not particularly limited, and it can be formed by a method such as a vacuum deposition method, a sputtering method, or an organic metal chemical vapor deposition (MOCVD) method.

(window layer)

As described above, an insulating layer as a window layer may be provided between the buffer layer 40 and the light-transmitting conductive layer 60. The insulating layer is an intermediate layer for taking in light, and prevents recombination of electrons excited by light and holes, and contributes to improving power generation efficiency. The composition of the insulating layer is also not particularly limited, but is preferably i-ZnO or the like. The film thickness here is not particularly limited, and is preferably 10 nm to 2 μm, more preferably 15 to 200 nm. The film formation method is not limited, but sputtering and MOCVD are more suitable. On the other hand, in the case where the buffer layer 40 is produced by the liquid phase method, since the manufacturing process is simple, it is preferable to apply the liquid phase method.

(translucent conductive layer)

The translucent conductive layer (transparent electrode) 60 is a layer that functions as an upper electrode in response to the bottom electrode 20 while the light is taken in, and the current generated by the photoelectric conversion layer 30 flows in. The composition of the light-transmitting conductive layer 60 is not particularly limited, and n-ZnO such as ZnO:Al or the like is preferable. The film thickness of the light-transmitting conductive layer 60 is not particularly limited, but is preferably 50 nm to 2 μm. The film forming method of the light-transmitting conductive layer 60 is not particularly limited, and is similar to the window layer, and is preferably an MOCVD method, a reactive plasma vapor deposition method, or an ion plating method. On the other hand, since the manufacturing process is relatively simple, it is preferable to apply the liquid phase method.

(gate)

The gate electrode 70 is an electrode that is used to extract electric power from the element, and its main component is not particularly limited, and is exemplified by Al or the like. The film thickness of the gate electrode 70 is also not particularly limited, and is preferably 0.1 to 3 μm.

The photoelectric conversion element 1 of the present embodiment has the above configuration.

In the method of producing the photoelectric conversion element 1, the method of forming the buffer layer is not particularly limited as long as the buffer layer is formed by the method for producing the buffer layer, and various film formation methods in the description of the respective layers can be applied. .

The photoelectric conversion element 1 can be advantageously used for a solar cell or the like. The photoelectric conversion element 1 is integrated and a cover glass, a protective film, or the like is attached as needed to prepare a solar cell.

3 is a plan view showing a solar cell 2 in which the photoelectric conversion element 1 is formed by a majority of integration, and FIG. 4 is an enlarged cross-sectional view showing a portion of FIG.

As shown in FIG. 3 and FIG. 4, the solar cell 2 is a photoelectric conversion element (battery cell) formed by laminating a bottom electrode 20, a photoelectric conversion layer 30, a buffer layer 40, and a light-transmitting conductive layer 60 on a single substrate 10. 1 is made up of a plurality of series connected.

After the bottom electrode 20 is formed on the substrate 10, the electrode layer is scribed to form a first scribe line 61, and the photoelectric conversion layer 30 and the buffer layer 40 are sequentially formed thereon, and formed. These are passed through a scribe line 62 on the surface of the electrode layer, and a light-transmitting conductive layer (upper electrode) 60 is laminated, by forming a scribe line 64 from the surface of the light-transmitting conductive layer 60 to the bottom electrode 20 ( The scribe line) can obtain the solar cell 2 in which a plurality of battery cells 1 are integrated. The adjacent battery cells 1 are separated by a scribe line 64, and the adjacent battery cells 1 are connected in series via a light-transmitting conductive layer material embedded in the scribe line 62.

Thereby, the solar cells in which the plurality of photoelectric conversion elements 1 are connected in series are affected by the lower efficiency of the cell characteristics of the plurality of photoelectric conversion elements, and in the past, the average photoelectric conversion efficiency by the battery cells was only expected, but Not necessarily able to get To this efficiency. However, in the photoelectric conversion element of the present invention, since the fluctuation in efficiency between the elements is suppressed to be small, the efficiency obtained from the single cell can be realized, and the efficiency of the integrated solar cell can be expected, and it can be more stable than in the past. High photoelectric conversion efficiency of solar cells.

"Design changes"

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit and scope of the invention.

Description of the embodiments and comparative examples of the present invention.

<Substrate ~ Photoelectric Conversion Layer>

For the substrate, the substrate 1 and the substrate 2 described below are prepared.

Substrate 1: Soda-lime glass substrate

Substrate 2: 100 μm thick stainless steel (SUS) - Anodized 30 μm thick Al composite substrate was placed on the AAO surface of an anodized substrate on which an anodic aluminum oxide (AAO) was formed on the surface of Al. A substrate having a soda lime glass (SLG) layer. The thickness of each layer of the substrate 2 was SUS (100 μm), Al (20 μm), AAO (10 μm), and SLG (0.2 μm).

On the substrate 1 or the substrate 2, a 0.8 μm thick Mo bottom electrode was formed by sputtering, and a film thickness of 1.8 μm as a photoelectric conversion layer was formed on the bottom electrode of Mo by a three-stage method. Cu(In _0.7 Ga _0.3 )Se ₂ layer. In addition, this is called a buffer film formation substrate.

<surface treatment>

Prepare a reaction tank in which a 10% KCN aqueous solution is placed, and buffer the substrate for film formation The surface of the outermost CIGS layer was immersed for 3 minutes at room temperature to remove impurities from the surface of the CIGS layer. After taking out, wash with plenty of water.

After the formation of the Mo electrode and the CIGS layer and the surface treatment using the substrate 1 or the substrate 2, the buffer layer 40 was formed on the surface of the CIGS layer under the conditions of the following Examples 1 to 10 and Comparative Examples 1 to 3.

(Example 1)

The substrate 1 is used.

A zinc sulfate aqueous solution (0.18 [M]) as an aqueous solution (I), a thiourea solution (thiourea 0.30 [M]) as an aqueous solution (II), and an aqueous solution of trisodium citrate as an aqueous solution (III) were separately prepared (2.4 [ M]) and ammonia water (0.3 [M]) as an aqueous solution (IV). Next, I, II, and III in each of the aqueous solutions are mixed in the same volume, and a mixed solution composed of zinc sulfate 0.06 [M], thiourea 0.10 [M], and trisodium citrate 0.8 [M] is completed. This mixed solution was mixed with 0.3 [M] of aqueous ammonia in the same volume to obtain a reaction liquid 1. When the aqueous solutions (I) to (IV) are mixed, the aqueous solution (IV) must be added at the end. For the reaction liquid to be transparent, it is quite important to add the aqueous solution (IV) at the end. The reaction solution 1 was zinc sulfate 0.03 [M], thiourea 0.05 [M], trisodium citrate 0.4 [M], and ammonia 0.15 [M]. The alkali metal in the reaction liquid 1 was sodium, and the concentration was 1.2M. The obtained reaction solution 1 had a pH of 10.4.

Next, on the surface of the photoelectric conversion layer (CIGS) on the outermost surface of the buffer layer film-forming substrate, Zn(S, O) and/or Zn (S, O, Zn(S, O) and/or Zn (S, O) are formed by the CBD method using the reaction solution 1. OH) A buffer layer as a main component. Specifically, the substrate for buffer film formation was immersed for 120 minutes in 500 ml of a reaction liquid adjusted to a temperature of 90 ° C, and then the substrate was placed. After taking out, the surface was sufficiently washed with pure water, and the substrate was dried at room temperature. In the step of immersing the substrate in the reaction liquid, the substrate is provided so that the substrate surface is vertical with respect to the bottom surface of the container of the reaction liquid.

After the buffer layer was formed into a film, annealing treatment was performed at 200 ° C for one hour to form a buffer layer.

(Example 2)

A buffer layer was formed in the same manner as in Example 1 except that the substrate 2 was used instead of the substrate 1.

(Example 3)

A buffer layer was formed in the same manner as in Example 1 except that the immersion time (reaction time) of the buffer film formation substrate was 60 minutes.

(Example 4)

A buffer layer was formed in the same manner as in Example 3 except that the substrate 2 was used instead of the substrate 1.

(Example 5)

A buffer layer was formed in the same manner as in Example 1 except that the immersion time (reaction time) of the buffer film formation substrate was 90 minutes.

(Example 6)

A buffer layer was formed in the same manner as in Example 5 except that the substrate 2 was used instead of the substrate 1.

(Example 7)

Zinc sulfate 0.03 [M], thiourea 0.05 [M], tripotassium citrate 0.4 [M], ammonia The reaction liquid 2 was prepared at 0.15 [M].

A buffer layer was formed in the same manner as in Example 1 except that this reaction liquid 2 was used.

(Example 8)

A buffer layer was formed in the same manner as in Example 7 except that the substrate 2 was used instead of the substrate 1.

(Example 9)

The reaction liquid 3 was prepared with zinc sulfate 0.03 [M], thiourea 0.05 [M], trilithium citrate 0.4 [M], and ammonia 0.15 [M]. A buffer layer was formed in the same manner as in Example 1 except that this reaction liquid 3 was used.

(Embodiment 10)

A buffer layer was formed in the same manner as in Example 9 except that the substrate 2 was used instead of the substrate 1.

(Comparative Example 1)

The reaction liquid 4 was prepared with zinc sulfate 0.16 [M], thiourea 0.6 [M], and ammonia 7.5 [M]. That is, the reaction liquid 4 of Comparative Example 1 did not contain an alkali metal ion.

In the reaction liquid 4, a buffer layer was formed in the same manner as in Example 1 except that the temperature of the reaction liquid was 80 ° C, and the immersion time (reaction time) of the substrate for buffer film formation was 40 minutes.

(Comparative Example 2)

The reaction liquid 5 was prepared with zinc sulfate 0.025 [M], thiourea 0.4 [M], and ammonia 2.5 [M]. In the case of the reaction liquids 1 to 4, the sources of Zn are different, and the alkali metal ions are not contained in the reaction liquid 5.

The reaction liquid 5 was used, and a buffer layer was formed in the same manner as in Example 1 except that the temperature of the reaction liquid was 80 ° C, and the immersion time (reaction time) of the substrate for buffer film formation was 180 minutes.

(Comparative Example 3)

The reaction liquid 6 was prepared with zinc sulfate 0.03 [M], thiourea 0.05 [M], trisodium citrate 0.03 [M], and ammonia 0.15 [M]. The alkali metal ion concentration in the reaction liquid 6 was 0.09 [M].

A buffer layer was formed in the same manner as in Example 3 except that this reaction liquid 6 was used.

The buffer layer film formation conditions of the respective examples and comparative examples are summarized in Table 1.

<Evaluation of the composition of the buffer layer>

The obtained 1 cm square CIGS substrate (the CIGS layer was formed on the substrate) was obtained under the same conditions as in Examples 1 to 10 and Comparative Examples 1 to 3 until the buffer layer was formed. Samples were analyzed for composition. In the measurement, composition analysis of the buffer layer was performed in the depth direction by X-ray photoelectron spectroscopy. As an example, the results of Example 3 are shown in FIG. The depth direction etched from the surface of the buffer layer in Fig. 5 is shown on the horizontal axis, and the concentration of each element is shown on the vertical axis. In addition, the concentration shown in FIG. 5 is the respective element concentration with respect to the total content of the elements O, C, Na, S, Zn, Cu, Ga, In, and Se which constitute a sample. Although the measurement is performed on all of these elements, only O, C, S, Zn, and Cu are shown in FIG.

Further, the XPS measurement accompanying the etching was carried out under the following conditions. In Fig. 5, the horizontal axis represents the etching depth [nm] obtained from the sputtering time (minutes). The etching depth converted from the sputtering time is calculated by using the etching rate calculated from the SiO ₂ film (substrate is a Si wafer) of a known film thickness as a standard sample. The conversion of the thickness of the buffer layer is calculated as the maximum concentration of the S component in the buffer layer, based on the position at which the concentration is halved.

XPS analysis

Device: X-ray photoelectron spectroscopy set with Quantera SXM manufactured by PHI

X-ray source: single crystal spectroscopic AlK α line

Output / analysis range: 25W / φ 100μm

Pass Energy: Analysis of depth direction Narrow Scan-280.0ev (0.25eV/Step)

Geometry: θ=45° (angle between the sample surface and the detector)

Ar ⁺ etching conditions

Acceleration voltage: 1kV, raster size: 2*2mm, rate: about 2.6nm/min (in the case of SiO ₂ )

As shown in Fig. 5, the thickness of the buffer layer was measured by XPS, and the distribution of each component in the buffer layer was determined. This result confirms the presence of both S and O in the buffer layer. Further, with respect to the maximum concentration of S, the thickness of the buffer layer was calculated by calculating the position at which the concentration was halved. The thicknesses of the respective examples and comparative examples are shown in Table 2, respectively. The type of alkali metal can be identified from the position where the peak of the XPS spectrum is located. Further, since the thickness of the buffer layer is obtained by the above-described method, the average concentration of the alkali metal in the buffer layer can be calculated from the concentration distribution in the etching depth direction of the alkali metal.

The presence of Zn was also confirmed at the position where S was not detected. This should be due to the diffusion of Zn ²⁺ in the CIGS layer during the CBD step.

Further, in Table 2, the ratio of the S component in the buffer layer is represented by an S/(S+O) value. The S/(S+O) value was 0.51 to 0.55 in Examples 1 to 8, and there was almost no difference, and in Comparative Examples 1 to 3, there was a deviation of 0.42 to 0.6. However, even if it was produced under any of the conditions of Examples 1 to 8 and Comparative Examples 1 to 3, it can be said that the composition of the buffer layer contained S, O or S, O, OH.

<Production of Photoelectric Conversion Element - Continued>

On the buffer layers prepared in Examples 1 to 10 and Comparative Examples 1 to 3, by sputtering method A light-transmitting conductive film containing an Al-conductive zinc oxide film having a film thickness of 300 nm was formed. Thereafter, an Al electrode as a gate electrode was formed by a vapor deposition method to fabricate a photoelectric conversion element (a solar cell of a single cell).

Further, eight battery cells were produced for each of the examples and comparative examples. The eight battery cells in each of the examples were formed by cutting out a plurality of layers on one substrate, and cutting them at a predetermined size, which were obtained in the same step at the same time.

<Evaluation of photoelectric conversion efficiency>

With respect to the obtained photoelectric conversion elements (eight battery cells) of the examples and the comparative examples, the use of pseudo-sunlight at air mass (AM) = 1.5, 100 mW/cm ² using a solar simulator was used. Under the conditions, the photoelectric conversion efficiency is measured. In addition, the measurement of the photoelectric conversion efficiency was performed after 30 minutes after the light irradiation was performed.

The results obtained are shown in Table 2. The maximum value, the average value, or the minimum value of the photoelectric conversion efficiencies of the eight battery cells of the respective examples and comparative examples are shown in Table 2, and the coefficient of variation obtained from these is further shown. The coefficient of variation is a ratio of the standard deviation of the photoelectric conversion efficiency of eight battery cells divided by the average value of the photoelectric conversion efficiencies of eight battery cells (herein expressed as a percentage).

As shown in Table 2, the coefficient of variation of the examples of the present invention was 12% or less, and it was suppressed to 10% or less except for Example 5. Considering that the comparative examples are all having a coefficient of variation of 20% or more, it is apparent that the embodiment of the present invention can obtain an effect of suppressing a high coefficient of variation. In Comparative Example 1 and Comparative Example 2 in which a buffer layer was formed using a reaction liquid containing no metal source of an alkali metal, no alkali metal was detected in the buffer layer, and these coefficient of variation were extremely large. In the examples 1 to 8, when the alkali metal contained 0.7 at% or more in the buffer layer, the coefficient of variation was remarkably small as compared with the comparative example 3 in which the content was 0.05 at%. As an alkali metal, the addition of any of sodium, potassium, and lithium can also achieve a high uniformity effect.

In the above, although the embodiment in which the buffer layer contains the Zn-based compound is shown, the buffer layer contains the Cd-based compound, the In-based compound, or the Sn-based compound, and it is considered that the buffer layer can be contained in the buffer layer. The alkali metal causes a change in the band structure, and an effect of suppressing recombination of carriers generated in the photoelectric conversion layer is produced, and it is considered that an effect of improving the uniformity of the photoelectric conversion characteristics can be obtained.

Claims (9)

A photoelectric conversion element is a photoelectric conversion element in which a bottom electrode layer, a photoelectric conversion layer, a buffer layer, and a light-transmitting conductive layer are laminated on a substrate, and the photoelectric conversion layer contains an Ib group element, a group IIIb element, and a group VIb element. a compound semiconductor of a chalcopyrite structure as at least one of the above, characterized in that the buffer layer comprises a compound containing an alkali metal; the alkali metal is at least one of lithium, sodium and potassium; and the alkali in the above compound The content of the metal is 0.1 at% or more and 5 at% or less. The photoelectric conversion element according to claim 1, wherein the compound constituting the buffer layer contains a metal, sulfur, and oxygen, and the metal is at least one selected from the group consisting of Cd, Zn, In, and Sn. The photoelectric conversion element according to claim 2, wherein the metal is Zn. The photoelectric conversion element according to claim 1, wherein the content of the alkali metal is 0.5 at% or more and 2.5 at% or less. The photoelectric conversion element according to claim 1, wherein the buffer layer has a thickness of 1 nm or more and 100 nm or less. The photoelectric conversion element according to claim 1, wherein the Group Ib element is at least one selected from the group consisting of Cu and Ag, and the Group IIIb element is selected from the group consisting of Al, Ga, and In. At least one of the group, the group VIb element is at least one selected from the group consisting of S, Se, and Te. A solar cell, which is formed by integrating a plurality of photoelectric conversion elements according to any one of claims 1 to 6. A method for producing a buffer layer, which is a method for producing a buffer layer in a photoelectric conversion element in which a bottom electrode layer, a photoelectric conversion layer, a buffer layer, and a light-transmitting conductive layer are laminated on a substrate, wherein the photoelectric conversion layer contains an Ib group A compound semiconductor having a chalcopyrite structure of at least one of an element, a group IIIb element, and a group VIb element as a main component, which is prepared by chemical bath deposition containing a predetermined metal ion, thiourea, or an alkali metal ion of 1 M or more. In the reaction liquid, at least the surface of the photoelectric conversion layer of the buffer film-forming substrate on which the bottom electrode layer and the photoelectric conversion layer are laminated in this order are brought into contact with the reaction liquid, whereby the photoelectric conversion layer is A buffer layer is deposited on it. A method for producing a photoelectric conversion element, which is a method for producing a photoelectric conversion element in which a bottom electrode layer, a photoelectric conversion layer, a buffer layer, and a light-transmitting conductive layer are laminated on a substrate, wherein the photoelectric conversion layer contains a group Ib element, IIIb The compound semiconductor of the chalcopyrite structure of at least one of the group element and the group VIb element is a main component, and the buffer layer is formed by the method for producing a buffer layer according to the eighth aspect of the invention.