JP2012079727A - Photoelectric conversion element and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the following problems: the loss of Cu is caused on a light absorption layer side in manufacturing or due to aged deterioration, so that photoelectric conversion efficiency may be decreased; and mutual diffusion between a buffer layer and a light absorption layer becomes excessive, so that photoelectric conversion efficiency may be decreased.SOLUTION: A photoelectric conversion element includes: a light absorption layer which includes a compound semiconductor comprising Cu, a III-B group element and Se and capable of performing photoelectric conversion; a semiconductor layer provided on one side of the light absorption layer and including an element group A (the element group A is at least one selected from among Cd, Zn and In) and S; and an intermediate layer provided between the light absorption layer and the semiconductor layer and including the element group A, Cu and S.

Description

  The present application relates to a photoelectric conversion element and a manufacturing method thereof.

  A photoelectric conversion element having a higher photoelectric conversion efficiency has been demanded year by year, and a CIS film or a CIGS film is used as a light absorption layer of such a photoelectric conversion element, and is optimally stacked on the light absorption layer. The buffer layer is being developed. For example, Patent Document 1 describes a photoelectric conversion element in which an n-type mixed layer in which Cd and CIS are vapor-deposited simultaneously as a buffer layer is formed on a p-type CIS film that is a light absorption layer.

JP-A-6-45248

  However, in the photoelectric conversion element of Patent Document 1, Cd, which is a constituent element of the buffer layer, tends to diffuse into the light absorption layer during manufacturing or due to aging. If the diffusion of Cd proceeds excessively, Cd deficiency may occur in the buffer layer and the photoelectric conversion efficiency may decrease. Therefore, an object of the present invention is to solve such problems and to provide a highly reliable photoelectric conversion element capable of suppressing a decrease in photoelectric conversion efficiency.

  In view of the above, the photoelectric conversion element of the present invention includes a light absorption layer containing a compound semiconductor capable of photoelectric conversion having Cu, a group III-B element and Se, and an element group A provided on one side of the light absorption layer. (Here, element group A is at least one of Cd, Zn and In) and S, and the element group A, Cu and S provided between the light absorption layer and the semiconductor layer. And an intermediate layer.

  In the method for producing a photoelectric conversion element of the present invention, the light absorption layer is immersed in an aqueous ammonia solution containing the element groups A and S, and then the temperature of the aqueous ammonia solution is monotonously increased so that the light absorption layer is formed on the light absorption layer. A solution growth step of forming an element group A sulfide layer on the substrate, and heat-treating the element group A sulfide layer after the solution growth step so that the element group A sulfide layer is formed into the intermediate layer and the semiconductor layer. Heat treatment step.

  According to the present invention, even when the element group A, which is a constituent element of the semiconductor layer, diffuses from the intermediate layer or the semiconductor layer to the light absorption layer side, the defect of the element group A is compensated by Cu contained in the intermediate layer. Can do. As a result, a decrease in photoelectric conversion efficiency can be suppressed over a long period.

It is a cross-sectional schematic diagram of the photoelectric conversion element concerning embodiment of this invention. It is an expanded sectional photograph of the photoelectric conversion element concerning embodiment of this invention. It is a graph which shows the composition distribution of the photoelectric conversion element concerning embodiment of this invention.

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

<Board>
In FIG. 1, a substrate 5 is for supporting a photoelectric conversion element 10. Examples of the material used for the substrate 5 include glass, ceramics, resin, and metal. Here, a blue plate glass (soda lime glass) having a thickness of about 1 to 3 mm is used as the substrate 5.

<Lower electrode>
The lower electrode layer 4 is a conductor made of a metal such as Mo, Al, Ti, Ta, or Au provided on one main surface of the substrate 5 or a laminated structure of these metals. The lower electrode layer 4 is formed to a thickness of about 0.2 to 1 μm using a known thin film forming method such as sputtering or vapor deposition.

<Light absorption layer>
The light absorption layer 1 includes a chalcopyrite-based (hereinafter also referred to as CIS-based) Cu, III-B group element and Se-convertible compound semiconductor provided on the lower electrode layer 4, and is p-type Have the conductivity type. The light absorption layer 1 has a thickness of about 1 to 3 μm.

Here, the I-III-VI group compound is a compound of a group IB element, a group IIIB element, and a group VIB element (in other words, a group 11 element, a group 13 element, or a group 16 element). Examples of this embodiment include Cu (In, Ga) Se ₂ (also referred to as CIGS).

  Such a light absorption layer 1 can be formed by a so-called vacuum process such as a sputtering method or a vapor deposition method, and a solution containing the constituent elements of the light absorption layer 1 is applied on the lower electrode layer 4, and then It can also be formed by a so-called coating method or printing method in which drying and heat treatment are performed.

<Semiconductor layer>
The semiconductor layer 2 is provided on the light absorption layer 1 and has an n-type conductivity type different from the conductivity type of the light absorption layer 1. The semiconductor layer 2 is a compound semiconductor containing element group A (where element group A is at least one of Cd, Zn, and In) and S. Such a compound semiconductor includes a sulfide of element group A (hereinafter, the sulfide of element group A is referred to as element group A sulfide), and includes a CdS compound, a ZnS compound, and In ₂ S _3. System compounds. The CdS compound means that it contains CdS but may be a mixed crystal compound containing Cd (OH) ₂ or CdO. Similarly, a ZnS-based compound means that a mixed crystal compound containing ZnS but also containing Zn (OH) ₂ or ZnO may be used. Similarly, an In ₂ S ₃ -based compound includes In ₂ S ₃ , but may also be a mixed crystal compound containing In (OH) ₃ or In ₂ O ₃ in addition thereto.

  In the photoelectric conversion element 10, since photoelectric conversion occurs in the light absorption layer 1 and the semiconductor layer 2 constituting the heterojunction, the light absorption layer 1 and the semiconductor layer 2 are photoelectric conversion layers.

  Moreover, in this embodiment, it is preferable that the semiconductor layer 2 is comprised by the CBD method, for example by CdS type composition, and is formed in thickness of 1-30 nm.

<Upper electrode layer>
The upper electrode layer 6 is a transparent conductive film having an n-type conductivity provided on the semiconductor layer 2. The upper electrode layer 6 is provided as an electrode for extracting charges generated in the photoelectric conversion layer through the semiconductor layer 2.

  The upper electrode layer 6 is made of a material having a resistivity lower than that of the semiconductor layer 2, for example, indium oxide (ITO) containing tin.

  The upper electrode layer 6 is formed by sputtering, vapor deposition, or the like.

  Note that the semiconductor layer 2 and the upper electrode layer 6 are preferably made of a material having light transmittance with respect to the wavelength region of light absorbed by the light absorption layer 1, and the semiconductor layer 2 and the upper electrode layer 6. Are preferably substantially the same in refractive index. Thereby, the fall of the light absorption efficiency in the light absorption layer 1 is suppressed.

<Grid electrode>
The grid electrode 7 includes a current collector made of a metal such as Ag and a connecting part (not shown), and plays a role of collecting charges generated in the photoelectric conversion element 10 and taken out in the upper electrode layer 6. Thereby, the upper electrode layer 6 can be thinned.

<Intermediate layer>
The intermediate layer 3 is provided between the light absorption layer 1 and the semiconductor layer 2 and contains element groups A, Cu, and S.

  For example, as shown in FIG. 1, with respect to the laminated cross-section, a CuInGaSe-based composition is used as the light-absorbing layer 1 including a compound semiconductor capable of photoelectric conversion, and a CdS-based semiconductor layer 2 is provided on one side of the light-absorbing layer 1. When the composition of the surface is analyzed at each point shown in FIG. 2 in the case where the composition is a CuCdS-based composition as the intermediate layer 3 provided between the light absorption layer 1 and the semiconductor layer 2, the Cu of FIG. , Cd, S composition distribution graph.

  Furthermore, in the photoelectric conversion element according to the embodiment of the present invention, if the average composition ratio of the element groups A, Cu, and S in the intermediate layer 3 is set to Cu> S> element group A in atomic%, the semiconductor layer generated by secular change As the number of missing portions of the element A group, such as Cd, increases at 2, the defect becomes easier to compensate.

  Furthermore, in the photoelectric conversion element according to the embodiment of the present invention, the element group A is at least one of Cd and Zn, the light absorption layer 1 further includes the element groups A and S, Cu in the light absorption layer 1, element group Assuming that the average composition ratio of A and S is Cu> element group A> S in atomic%, pn homo is formed on the intermediate layer 3 side surface portion of the light absorption layer 1, and the light absorption layer 1 And the intermediate layer 3 contain each other's constituent elements and the composition approaches, so that the heterojunction can be made better. As a result, the photoelectric conversion efficiency can be further increased.

  Furthermore, in the photoelectric conversion element according to the embodiment of the present invention, the semiconductor layer 2 further includes Cu, and the average composition ratio of the element groups A, S, and Cu in the semiconductor layer 2 is S> element group A> Cu in atomic%. If it exists, the thermodynamic characteristic of the semiconductor layer 2 and the intermediate | middle layer 3 can be closely approached, and the failure | damage by stress can be suppressed.

  Furthermore, in the photoelectric conversion element according to the embodiment of the present invention, when the composition ratio of the element group A in the intermediate layer 3 is as small as the light absorption layer 1 side and the composition ratio of Cu is as large as the light absorption layer 1 side, Excessive diffusion of the element A group into the light absorption layer 1 can be controlled. Therefore, it can suppress that the semiconductor characteristic of the light absorption layer 1 changes, and can maintain high photoelectric conversion efficiency favorably over a long period of time.

<Method for producing photoelectric conversion element>
Next, a manufacturing process of the photoelectric conversion device having the above configuration will be described.

  In the following, a light absorption layer 1 (for example, CIGS containing Cu, In, Ga and Se) made of an I-III-VI group compound semiconductor is formed by a coating method, and further, the intermediate layer 3 and the semiconductor layer An example in which two or more are formed will be described.

  A lower electrode layer 4 made of Mo is formed on substantially the entire surface of the cleaned substrate 5 by sputtering. Then, the light absorption layer 1, an intermediate layer 3 described later, and the semiconductor layer 2 are sequentially formed on the lower electrode layer 4.

  In the light absorption layer 1, first, after the lower electrode layer 4 is formed, a solution for forming the light absorption layer 1 is applied to the surface of the lower electrode layer 4, and a film is formed by drying. Then, the light absorption layer 1 is formed by heat-treating the coating.

  The solution for forming the light absorption layer 1 is prepared by directly dissolving a group IB metal and a group III-B metal in a solvent containing a chalcogen element-containing compound and a basic organic solvent. The total concentration of the group B metal and the group III-B metal is 1% by weight or more.

  Note that various methods such as spin coater, screen printing, dipping, spraying, and die coater can be applied to the solution.

  The chalcogen element-containing organic compound is an organic compound containing a chalcogen element. As a chalcogen element, S, Se, and Te among VI-B group elements are said. Examples of the chalcogen element-containing organic compound include thiol, sulfide, selenol, and Ternol.

  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 to 300 ° C. The heat treatment is preferably performed in a reducing atmosphere such as hydrogen or nitrogen atmosphere to prevent oxidation. The heat treatment temperature is, for example, 400 to 600 ° C.

  After the light absorption layer 1 is formed, the intermediate layer 3 and the semiconductor layer 2 are formed by the CBD method, but it is preferable that the thickness be such that the light absorption layer 1 can be protected from damage due to sputtering in a subsequent step.

  Hereinafter, the manufacturing method of the intermediate | middle layer 3 and the semiconductor layer 2 is demonstrated in detail.

  First, after the light absorption layer 1 is immersed in an aqueous ammonia solution containing the element groups A and S, the element group A sulfide layer is formed on the light absorption layer 1 by monotonically increasing the temperature of the aqueous ammonia solution (this step) Is called a solution growth process). Then, after the solution growth step, the element group A sulfide layer can be heat treated to make the element group A sulfide layer into the intermediate layer 3 and the semiconductor layer 2 (this step is referred to as a heat treatment step).

For example, an NH ₃ solution of ph 11 to 13 containing CdI _{2 as} a Cd source and thiourea SC (NH ₂ ) _{2 as} an S source is monotonically increased from 30 ° C. to 53 ° C. over 1 to 10 minutes. And hold at a constant temperature from 53 ° C. over 1 to 10 minutes.

By monotonously increasing the temperature in this way, the film formation rate is increased by increasing the film formation speed in the first half of forming the element group A sulfide layer, and the film density is increased by increasing the film formation speed in the second half. Thereby, an element group A sulfide layer having a high film density on the light absorption layer 1 side and a low film density on the upper electrode layer 6 side can be obtained.

  Then, after such a solution growth step, when heat treatment is performed, the element group A sulfide layer actively diffuses the element group A toward the light absorption layer 1 because the film density is high at the site on the light absorption layer 1 side. It will be. Then, it is considered that Cu is positively diffused from the light absorption layer 1 where the element group A is missing, and as a result, mutual diffusion between Cu and the element group A occurs and the intermediate layer 3 is formed. Such a heat treatment step is preferably a step of heat treatment at 100 to 300 ° C. for 3 to 180 minutes in a nitrogen atmosphere.

  On the other hand, the portion of the element group A sulfide layer having a low film density on the side opposite to the light absorbing layer 1 is in a state where the element group A (for example, Cd) having a relatively large atomic radius does not diffuse and remains to some extent. It is considered that the semiconductor layer 2 is formed by the heat treatment step.

  Alternatively, even if the heat treatment as described above is not performed separately, if the deposition temperature in the solution growth process is high to some extent, Cu is dissolved from the light absorption layer 1 into the solution in the first half of the deposition of the element group A sulfide layer. The element group A sulfide layer grows while taking in the dissolved Cu. Thereby, the intermediate layer 3 can be formed. In the latter half of the formation of the element group A sulfide layer, the dissolution of Cu is suppressed by the growth of the element group A sulfide layer, and the element group A sulfide layer grows in this state. Thereby, the semiconductor layer 2 can be formed.

  Here, in the case where InS is formed as the element group A sulfide layer, the film may be formed using an acidic solution instead of an aqueous ammonia solution.

  In the present embodiment, after the intermediate layer 3 and the semiconductor layer 2 are formed, indium oxide (ITO) containing tin or the like is formed as the upper electrode layer 6 by sputtering or vapor deposition.

  After the upper electrode layer 6 is formed, the grid electrode 7 is formed by printing a conductive paste in which a metal powder such as Ag is dispersed in a resin binder or the like, and drying and solidifying this.

1: Light absorption layer 2: Semiconductor layer 3: Intermediate layer 4: Lower electrode layer 5: Substrate 6: Upper electrode layer 7: Grid electrode 10: Photoelectric conversion element

Claims (6)

A light absorbing layer comprising a compound semiconductor capable of photoelectric conversion having Cu, a group III-B element and Se;
A semiconductor layer containing element group A (where element group A is at least one of Cd, Zn and In) and S provided on one side of the light absorption layer;
The photoelectric conversion element which has the intermediate | middle layer containing the said element group A, Cu, and S provided between the said light absorption layer and the said semiconductor layer.   2. The photoelectric conversion element according to claim 1, wherein an average composition ratio of the element groups A, Cu and S in the intermediate layer is Cu> S> element group A in atomic%.   The element group A is at least one of Cd and Zn, the light absorption layer further includes the element groups A and S, and an average composition ratio of Cu and the element groups A and S in the light absorption layer is an atom The photoelectric conversion element according to claim 1, wherein Cu> element group A> S in%.   The semiconductor layer further includes Cu, and an average composition ratio of the element groups A, S, and Cu in the semiconductor layer is S> element group A> Cu in atomic%. Photoelectric conversion element.   5. The photoelectric conversion element according to claim 1, wherein the composition ratio of the element group A in the intermediate layer is smaller toward the light absorption layer side, and the composition ratio of Cu is greater toward the light absorption layer side. It is a manufacturing method of the photoelectric conversion element in any one of Claims 1-5,
After immersing the light absorption layer in an aqueous ammonia solution containing the element groups A and S,
A solution growth step of forming an element group A sulfide layer on the light absorption layer by monotonically increasing the temperature of the aqueous ammonia solution;
A method for producing a photoelectric conversion element, comprising: a heat treatment step of heat-treating the element group A sulfide layer after the solution growth step so that the element group A sulfide layer becomes the intermediate layer and the semiconductor layer.