JP2012119351A - Photoelectric conversion element, method of manufacturing the same, and photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion element that is free from Cd and has high photoelectric conversion efficiency.SOLUTION: A photoelectric conversion element has: a light absorption layer that is provided on a lower electrode layer and contains Cu, a group III-B element, and a group VI-B element; and a semiconductor layer that is provided above the light absorption layer and contains a group II-VI compound or a group III-VI compound. Conductors containing at least one of an Ag element and a Pt element are scattered above the light absorption layer. The photoelectric conversion element further has a conductive layer containing at least one of the Ag element and the Pt element on the light absorption layer at the semiconductor layer side.

Description

  The present invention relates to a photoelectric conversion element, a manufacturing method thereof, and a photoelectric conversion apparatus.

  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.

  As such a buffer layer, for example, Patent Document 1 describes that a CdS film formed by thermal decomposition of an organic compound having a Cd—S bond is used as the buffer layer.

  Patent Document 2 describes that a CdS film formed by a CBD method is used as a buffer layer.

JP 2001-308353 A US Pat. No. 4611091

  In CIGS, it is known that recombination due to Cu deficiency is observed, and this deficiency causes recombination of current generated inside CIGS, which reduces conversion efficiency, but diffuses Cd during CdS film formation. It is known that it can be suppressed by making it.

  However, in recent years, the need for Cd-free has increased, and Cd diffusion cannot be used.

  Also, instead of forming a CdS film and diffusing Cd, if Cu is sputtered and annealed on CIGS, Cu deficiency can be compensated. However, in recent years, higher photoelectric conversion efficiency is required. became. In particular, the valence band and the conduction band of the Cd-free buffer layer are different from those of CIGS, and since the contact resistance is large, the FF is small and there is no degree of freedom in selecting the buffer layer.

  In view of the above, the present invention provides a light absorbing layer containing Cu, a group III-B element and a group VI-B element provided on the lower electrode layer, and a II-VI provided on the light absorbing layer. And a semiconductor layer containing a group III compound or a group III-VI compound, wherein the light absorbing layer is dotted with conductors containing at least one of an Ag element and a Pt element, and The semiconductor layer side of the light absorption layer has a conductive layer containing at least one of Ag element and Pt element.

Furthermore, the manufacturing method of the present invention includes a first step of forming a light absorption layer containing Cu, a group III-B element and a group VI-B element on the lower electrode layer, and an Ag element on the light absorption layer by a sputtering method. And a second step of forming a conductor containing at least one of Pt element and Pt element, and by annealing, at least one of Ag element and Pt element is thermally diffused from the conductor to the light absorption layer, and a part of the light absorption layer A semiconductor layer containing a II-VI group compound or a III-VI group compound on the light absorption layer on which the conductive layer is formed, and a third step of forming a conductive layer containing at least one of an Ag element and a Pt element. 4th process to form.

  According to the present invention, it is possible to facilitate the movement of charges at the interface between the light absorption layer and the semiconductor layer by interspersing the light absorption layer with a metal conductive layer that lowers the contact resistance.

  By reducing the contact resistance between the light absorption layer and the semiconductor layer, the conversion efficiency is improved and the degree of freedom in selecting the material of the semiconductor layer is also increased.

It is a perspective sectional view of the whole photoelectric conversion element composition of this embodiment. It is a cross-sectional schematic diagram of the manufacturing process and layer structure of the photoelectric conversion element of this embodiment. It is a cross-sectional schematic diagram of the manufacturing process and layer structure of the photoelectric conversion element of this embodiment. It is the cross-sectional schematic diagram which expanded the interface vicinity of the light absorption layer of the photoelectric conversion element of this embodiment, and a semiconductor layer. It is a schematic diagram of the light absorption layer surface of the photoelectric conversion element of this embodiment.

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

<Photoelectric conversion element>
As shown in FIG. 1, the photoelectric conversion device has a configuration in which a plurality of photoelectric conversion elements are arranged in parallel on a substrate.

  Each photoelectric conversion element 20 mainly includes a lower electrode 9, a light absorption layer 3, a first semiconductor layer 1, a second semiconductor layer 2, upper electrode layers 5 and 7, and a grid electrode 8.

  In the photoelectric conversion device 21, the main surface on the side where the upper electrode layers 5 and 7 and the grid electrode 8 are provided is the light receiving surface side.

<Board>
The substrate 1 is for supporting a plurality of photoelectric conversion elements 20. Examples of the material used for the substrate 1 include glass, ceramics, resin, and metal. Here, a blue plate glass (soda lime glass) having a thickness of about 1 to 3 mm is used as the substrate 1.

<Lower electrode>
The lower electrode layer 2 is a conductor made of a metal such as Mo, Al, Ti, Ta, or Au provided on one main surface of the substrate 1 or a laminated structure of these metals.

  The lower electrode layer 2 is formed to a thickness of about 0.2 to 1 μm using a known thin film forming method such as a sputtering method or a vapor deposition method.

<Light absorption layer>
The light absorption layer 3 is a p-type conductive layer made of a compound containing a chalcopyrite-based (hereinafter also referred to as CIS-based) Cu, III-B group element and VI-B group element provided on the lower electrode layer 9. A semiconductor layer having a mold. The light absorption layer 4 has a thickness of about 1 to 3 μm.

Such a light absorption layer 3 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 4 is applied on the lower electrode layer 9, and then It can also be formed by a so-called coating method or printing method in which drying and heat treatment are performed.

<Conductor>
The conductors 6 are elements or compounds containing at least one of Ag and Pt elements, and are scattered on the light absorption layer 3.

  As will be described later, the conductive layer 6 a is disposed between the light absorption layer 3 and the semiconductor layer 4, and diffuses an element or compound containing at least one of Ag and Pt elements from the conductor 6 to the light absorption layer 3. It plays the role of a diffusion source.

  Such a dynamic transmission 6a is formed into an island-like structure by depositing a compound containing at least one of Ag and Pt elements for a short time by sputtering.

<Conductive layer>
The conductive layer 6a is a state in which an element or compound containing at least one of Ag and Pt elements is diffused to the semiconductor layer 4 side of the light absorption layer 3, and at least of Ag and Pt elements in the light absorption layer 3 One layer has a relatively large composition ratio.

  As will be described later, the conductive layer 6a can reduce the contact resistance between the light absorption layer 3 and the semiconductor layer 4 and facilitate the movement of charges at the interface between the light absorption layer 3 and the semiconductor layer 4. .

  Such a conductive layer 6a is formed by thermally diffusing at least one of Ag and Pt from the conductor 6 to the light absorption layer 3 by annealing.

<Semiconductor layer>
The semiconductor layer 4 is provided on the light absorption layer, and has an n-type conductivity type different from the conductivity type of the light absorption layer 3. And a semiconductor layer containing a VI-B group element.

The semiconductor layer 4 is provided in a mode of heterojunction with the light absorption layer 3 via the Ag-doped layer,
In the photoelectric conversion element 20, photoelectric conversion occurs in the light absorption layer 3 or the semiconductor layer 4 constituting the heterojunction.

  In the present embodiment, the semiconductor layer 4 is preferably formed to a thickness of 1 to 30 nm by a CBD method (chemical bath film formation method).

<Upper electrode layer>
The upper electrode layer 7 is a transparent conductive film having an n-type conductivity provided on the first semiconductor layer 4a and the second semiconductor layer 4b.

  The upper electrode layer 7 is provided as an electrode for extracting charges generated in the photoelectric conversion layer through the first semiconductor layer 4a or the second semiconductor layer 4b, and the upper electrode layer 7 includes the first semiconductor layer 4a and the second semiconductor layer. It is made of a material having a lower resistivity than that of the layer 4b, for example, indium oxide (ITO) containing tin, and is formed by a sputtering method, a vapor deposition method, or the like.

The first semiconductor layer 4a, the second semiconductor layer 4b, and the upper electrode layer 7 are preferably made of a material having light transparency with respect to the wavelength region of light absorbed by the light absorption layer 3, The first semiconductor layer 4a, the second semiconductor layer 4b, and the upper electrode layer 7 preferably have substantially the same absolute refractive index. Thereby, the fall of the light absorption efficiency in the light absorption layer 3 is suppressed.

<Grid electrode>
The grid electrode 8 includes a current collecting portion 8a made of a metal such as Ag and a connecting portion 8b (not shown), and plays a role of collecting charges generated in the photoelectric conversion element 20 and taken out in the upper electrode layer 7. . Thereby, the upper electrode layer 7 can be thinned.

  The grid electrode 8 preferably has a width of 50 to 400 μm in consideration of conductivity and light transmittance to the light absorption layer 3.

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

  In the present embodiment, a light absorption layer containing Cu, a group III-B element and a group VI-B element provided on the lower electrode layer, and a group II-VI compound or a compound provided on the light absorption layer A photoelectric conversion element having a semiconductor layer containing a III-VI group compound, wherein a conductor containing at least one of an Ag element and a Pt element is scattered on the light absorption layer, and the semiconductor of the light absorption layer On the layer side, a conductive layer containing at least one of Ag element and Pt element is provided.

  Thereby, since the conductive layer 6a can reduce the contact resistance between the light absorption layer 3 and the semiconductor layer 4, the movement of charges at the interface between the light absorption layer 3 and the semiconductor layer 4 can be facilitated. In particular, when the conductive layer 6a is Ag, recombination can be reduced by the effect of compensating for Cu defects in the light absorption layer 3.

  In addition, the band gap of the conductive layer 6a on the surface of the light absorption layer 3 is larger than the remaining portion, and the photoelectric conversion efficiency can be further improved. For example, when the light absorption layer 3 is a Cu—In—Ga—Se compound (with a band gap of 1.1 eV), the conductive layer 6 a becomes an Ag—Cu—In—Ga—Se compound. The structure extends to 2 eV or more, and the photoelectric conversion efficiency can be further improved.

  Furthermore, in this embodiment, the area ratio of the area occupied by the conductor on the upper surface of the light absorption layer is 5 to 30%.

  If it is this range, it can reduce that the conductor 6 interrupts | blocks the light to the light absorption layer 3, and reduces photoelectric conversion efficiency on the contrary.

  Furthermore, in this embodiment, the average thickness of the conductor is 0.5 to 10 nm, and the average diameter of the conductor is 5 to 100 nm.

  If it is this range, since the magnitude | size of the conductor 6 can be made below into the wavelength which contributes effectively to photoelectric conversion, reflection and absorption of light can be reduced and the fall of the transmittance | permeability can be reduced.

  Furthermore, in this embodiment, the average thickness of the conductive layer is 50 to 100 nm.

  Within this range, the movement of charges at the interface between the light absorption layer 3 and the semiconductor layer 4 can be further facilitated. In particular, when the conductive layer 6a is Ag, recombination can be further reduced, and a material having a wider band gap can be obtained.

Moreover, the manufacturing method of the photoelectric conversion element of this embodiment includes the first step of forming a light absorption layer containing Cu, a group III-B element and a group VI-B element on the lower electrode layer, and a light absorption layer by a sputtering method. A second step of forming a conductor containing at least one of an Ag element and a Pt element;
A third step of thermally diffusing at least one of Ag element and Pt element from the conductor to the light absorption layer by annealing to form a conductive layer containing at least one of Ag element and Pt element in a part of the light absorption layer; And a fourth step of forming a semiconductor layer containing a II-VI group compound or a III-VI group compound on the light absorption layer on which the conductive layer is formed.

  Thereby, the conductors 6 can be appropriately scattered on the light absorption layer 3. This utilizes the property that the initial layer formed by the sputtering method in the second step forms an island-like structure. If the conductor 6 having such an island-like structure is thermally diffused by annealing in the third step, Each of the conductive layers 6a can be obtained by diffusing even in the in-plane direction.

  If the conductor 6 is formed on the entire surface of the light absorption layer 3, light transmission to the light absorption layer 3 is completely hindered.

(Sample preparation)
Samples were prepared by each of the following manufacturing methods.

  As a substrate 1, a 2 mm thick blue plate glass (soda lime glass) is used, and as a lower electrode layer 2, a conductor made of Mo is formed with a thickness of 0.5 μm using a sputtering method. A solution containing a -Ga-Se compound was applied on the lower electrode layer 9, and then dried and heat-treated to form a thickness of 2 m (first step).

  Next, Pt as Example 1 and Ag as Example 2 were formed in an island shape on the light absorption layer 3 by a sputtering method (0.3 kW, 0.4 Pa, 0.01 nm / second) to form a conductor 6. (Second step). Here, the film formation time was performed in a range where the conductor 6 was not continuously connected in the in-plane direction in terms of the film formation rate.

  Next, Pt as Example 1 and Ag as Example 2 were thermally diffused from the conductor 6 to the light absorption layer 3 by annealing (in a nitrogen atmosphere at 250 ° C. for 30 minutes) to form the conductive layer 6a (third step). .

  Next, after forming ZnS as a semiconductor layer 4 by 20 nm by CBD method (chemical bath film-forming method) and indium oxide (ITO) as 20 nm by sputtering method, vapor deposition method or the like as an upper electrode layer 7, a grid electrode 8 is formed. Formed.

(Evaluation methods)
The photoelectric conversion element according to the above-described manufacturing method was used as the embodiment shown in FIG. 1, and the photoelectric conversion efficiency was evaluated.

Example 1
The results of diffusing Pt in the light absorption layer 3 are shown in Table 1.

  Sample 2-21 having conductor 6 has higher photoelectric conversion efficiency than sample 1 having no conductor 6.

  Sample 3 in which the area ratio, the average thickness D1, and the average diameter R1 of the conductor 6 are ranges in which the contact resistance between the light absorption layer 3 and the semiconductor layer 4 is lowered and the light incident on the light absorption layer 3 is not disturbed. For -5, 8-10, and 13-15, particularly high conversion efficiency could be obtained.

  Moreover, it turned out that the thickness D2 of the conductive layer 6a improves the photoelectric conversion efficiency most in the range of 50-100 nm of the sample 18-20.

(Example 2)
The results of diffusing Ag in the light absorption layer 3 are shown in Table 2 below.

  Compared to the sample 1 that does not have the conductor 6, the sample 22-41 that has the conductor 6 has higher photoelectric conversion efficiency.

  Sample 23 in which the area ratio, the average thickness D1, and the average diameter R1 of the conductors 6 are ranges in which the contact resistance between the light absorption layer 3 and the semiconductor layer 4 is lowered and the light incident on the light absorption layer 3 is not hindered. For -25, 28-30 and 33-35, particularly high conversion efficiency could be obtained.

  Moreover, it turned out that the thickness D2 of the conductive layer 6a improves the photoelectric conversion efficiency most in the range of 50-100 nm of the sample 38-40.

  Compared to Example 2-21, the conversion efficiency of Example 22-41 is generally higher by about 1% because the conductive layer 6a becomes an Ag—Cu—In—Ga—Se compound. This is considered to be due to the band gap expanding to 1.2 eV or more.

1: Substrate 2: Lower electrode layer 3: Light absorption layer 4: Semiconductor layer 5, 7: Upper electrode layer 6: Conductor 6a: Conductive layer 8: Electrode 20: Photoelectric conversion element 21: Photoelectric conversion device

Claims (6)

A light absorbing layer containing Cu, III-B group element and VI-B group element provided on the lower electrode layer, and a II-VI group compound or III-VI group compound provided on the light absorbing layer A photoelectric conversion element having a semiconductor layer containing
On the light absorption layer are scattered conductors containing at least one of Ag element and Pt element,
A photoelectric conversion element having a conductive layer containing at least one of an Ag element and a Pt element on the semiconductor layer side of the light absorption layer.   The photoelectric conversion element according to claim 1, wherein an area ratio of an area occupied by the conductor on the upper surface of the light absorption layer is 5 to 30%.   The photoelectric conversion element according to claim 1 or 2, wherein an average thickness of the conductor is 0.5 to 10 nm, and an average diameter of the conductor is 5 to 100 nm.   The photoelectric conversion element according to claim 1, wherein the conductive layer has an average thickness of 50 to 100 nm. It is a manufacturing method of the photoelectric conversion element in any one of Claims 1-4,
Forming a light absorption layer containing Cu, a group III-B element and a group VI-B element on the lower electrode layer;
A second step of forming a conductor containing at least one of an Ag element and a Pt element on the light absorption layer by a sputtering method;
A third layer is formed by thermally diffusing at least one of an Ag element and a Pt element from the conductor to the light absorption layer by annealing to form at least one of an Ag element and a Pt element in a part of the light absorption layer. Process,
And a fourth step of forming a semiconductor layer containing a II-VI group compound or a III-VI group compound on the light absorption layer on which the conductive layer is formed.   The photoelectric conversion apparatus using the photoelectric conversion element in any one of Claims 1-4.

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