JP2014127580A - Method of manufacturing photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance photoelectric conversion efficiency of a photoelectric conversion device.SOLUTION: The method of manufacturing a photoelectric conversion device 11 comprises the steps of: preparing a light absorbing layer 3 which mainly contains a chalcopyrite compound containing a group 11 element, a group 13 element, and a group 16 element and in which the atomic concentration ratio of the group 16 element to the group 13 element is more than 2 at a surface part on one main surface side; and heating the light absorbing layer 3 in an atmosphere containing an organometallic compound of a group 12 element to diffuse the group 12 element into the surface part.

Description

  The present invention relates to a method for producing a photoelectric conversion device containing a I-III-VI group compound.

  As a photoelectric conversion device used for solar power generation or the like, there is one in which a semiconductor layer is formed of a chalcopyrite-based I-III-VI group compound such as CIS or CIGS.

In order to increase the photoelectric conversion efficiency of such a photoelectric conversion device, in Patent Document 1, a group 12 element (II-B group element) such as Zn or Cd is added to the surface of the semiconductor layer containing the I-III-VI group compound. A pn junction is formed in the semiconductor layer by doping to make the surface of the semiconductor layer n-type. As a method for doping a group 12 element into a semiconductor layer, a method is used in which an organometallic compound of a group 12 element is gasified and the group 12 element is thermally diffused into the semiconductor layer with this gas.

JP 2008-235794 A

  In the method as described in Patent Document 1, it is necessary to heat the semiconductor layer at 300 to 400 ° C. in order to sufficiently diffuse a sufficient amount of the group 12 element into the semiconductor layer. However, when diffusion is performed at such a high temperature, it is difficult to control the degree of diffusion of the group 12 element, and diffusion occurs not only to the surface of the semiconductor layer but also to the inside, and it is difficult to further improve the photoelectric conversion efficiency.

  The present invention has been made in view of the above problems, and an object thereof is to increase the photoelectric conversion efficiency of a photoelectric conversion device.

  A method for manufacturing a photoelectric conversion device according to an embodiment of the present invention mainly includes a chalcopyrite-based compound containing a group 11 element, a group 13 element, and a group 16 element, and 16 for the group 13 element in the surface portion on one main surface side. A step of preparing a light absorption layer having a group element atomic concentration ratio greater than 2, and heating the light absorption layer in an atmosphere containing an organometallic compound of a group 12 element to diffuse the group 12 element to the surface portion A process.

  ADVANTAGE OF THE INVENTION According to this invention, the photoelectric conversion efficiency of a photoelectric conversion apparatus can be improved.

It is a perspective view which shows an example of embodiment of a photoelectric conversion apparatus. It is sectional drawing of the photoelectric conversion apparatus of FIG. It is sectional drawing which shows typically the mode in the middle of manufacture of a photoelectric conversion apparatus. It is sectional drawing which shows typically the mode in the middle of manufacture of a photoelectric conversion apparatus. It is sectional drawing which shows typically the mode in the middle of manufacture of a photoelectric conversion apparatus. It is sectional drawing which shows typically the mode in the middle of manufacture of a photoelectric conversion apparatus. It is sectional drawing which shows typically the mode in the middle of manufacture of a photoelectric conversion apparatus.

  Hereinafter, a method for manufacturing a photoelectric conversion device according to an embodiment of the present invention will be described with reference to the drawings. In the drawings, parts having similar configurations and functions are denoted by the same reference numerals, and redundant description is omitted in the following description. Further, the drawings are schematically shown, and the sizes, positional relationships, and the like of various structures in the drawings are not accurately illustrated.

<(1) Configuration of photoelectric conversion device>
FIG. 1 is a perspective view showing an example of a photoelectric conversion device 11 manufactured by using a method for manufacturing a photoelectric conversion device according to an embodiment of the present invention. FIG. 2 is an XZ sectional view of the photoelectric conversion device 11 of FIG. 1 to 9 are provided with a right-handed XYZ coordinate system in which the arrangement direction of photoelectric conversion cells 10 (the horizontal direction in the drawing in FIG. 1) is the X-axis direction.

  The photoelectric conversion device 11 has a configuration in which a plurality of photoelectric conversion cells 10 are arranged in parallel on a substrate 1. In FIG. 1, only two photoelectric conversion cells 10 are shown for convenience of illustration, but an actual photoelectric conversion device 11 has a large number of photoelectric conversion cells in the X-axis direction of the drawing or further in the Y-axis direction of the drawing. The conversion cells 10 are arranged two-dimensionally (two-dimensionally).

  Each photoelectric conversion cell 10 mainly includes a lower electrode layer 2, a first semiconductor layer 3, a second semiconductor layer 4, an upper electrode layer 5, and a collecting electrode 7. In the photoelectric conversion device 11, the main surface on the side where the upper electrode layer 5 and the collecting electrode 7 are provided is a light receiving surface. In addition, the photoelectric conversion device 11 is provided with three types of groove portions such as first to third groove portions P1, P2, and P3.

  The substrate 1 supports the plurality of photoelectric conversion cells 10 and is made of, for example, a material such as glass, ceramics, resin, or metal. For example, as the substrate 1, blue plate glass (soda lime glass) having a thickness of about 1 to 3 mm may be used.

  The lower electrode layer 2 is a conductive layer provided on one main surface of the substrate 1. For example, molybdenum (Mo), aluminum (Al), titanium (Ti), tantalum (Ta), or gold (Au). Or a laminated structure of these metals. The lower electrode layer 2 has a thickness of about 0.2 to 1 μm and is formed by a known thin film forming method such as a sputtering method or a vapor deposition method.

The first semiconductor layer 3 is a semiconductor layer having a first conductivity type (here, p-type conductivity type) provided on the main surface (also referred to as one main surface) on the + Z side of the lower electrode layer 2. And has a thickness of about 1 to 3 μm. The first semiconductor layer 3 is a semiconductor layer containing a chalcopyrite-based I-III-VI group compound and functions as a light absorption layer. The I-III-VI group compound is a group IB element (also referred to as group 11 element), a group III-B element (also referred to as group 13 element), and a group VI-B element (also referred to as group 16 element). It is a compound containing. Examples of the I-III-VI group compound include Cu (In, Ga) Se ₂ (also referred to as CIGS), Cu (In, Ga) (Se, S) ₂ (also referred to as CIGSS), and CuInSe ₂ (also referred to as CIS). And the like). Cu (In, Ga) Se ₂ contains Cu as a group 11 element, contains In and Ga as a group 13 element, and contains Se as a group 16 element. Cu (In, Ga) (Se, S) ₂ contains Cu as a group 11 element, contains In and Ga as a group 13 element, and contains Se and S as a group 16 element.

The first semiconductor layer 3 has a surface portion on the opposite side (second semiconductor layer 4 side) from the lower electrode layer 2 (hereinafter, the surface of the first semiconductor layer 3 opposite to the lower electrode layer 2). The II-B group element (also referred to as a group 12 element) is doped on the portion of the first semiconductor layer 3). Thereby, carrier separation is favorably performed on the surface portion of the first semiconductor layer 3, and the photoelectric conversion efficiency is increased. As the group 12 element, Zn, Cd, or the like is used, and Zn may be used from the viewpoint of reducing the environmental load.

  The concentration of the group 12 element in the surface portion of the first semiconductor layer 3 may be, for example, 0.01 to 1 atomic%. The thickness of the surface portion 3a may be 0.01 to 0.3 times the thickness of the first semiconductor layer 3, for example.

  The second semiconductor layer 4 is a semiconductor layer provided on one main surface of the first semiconductor layer 3. The second semiconductor layer 4 has a conductivity type (here, n-type conductivity type) different from that of the first semiconductor layer 3. By joining the first semiconductor layer 3 and the second semiconductor layer 4, positive and negative carriers generated by photoelectric conversion in the first semiconductor layer 3 are favorably separated. Note that semiconductors having different conductivity types are semiconductors having different conductive carriers. Further, when the conductivity type of the first semiconductor layer 3 is p-type as described above, the conductivity type of the second semiconductor layer 4 may be i-type instead of n-type.

The second semiconductor layer 4 includes, for example, cadmium sulfide (CdS), indium sulfide (In ₂ S ₃ ), zinc sulfide (ZnS), zinc oxide (ZnO), indium selenide (In ₂ Se ₃ ), In (OH , S), (Zn, In) (Se, OH), and (Zn, Mg) O. From the viewpoint of reducing current loss, the second semiconductor layer 4 can have a resistivity of 1 Ω · cm or more. The second semiconductor layer 4 is formed by, for example, a solution growth method (also referred to as CBD method).

  The second semiconductor layer 4 has a thickness in the normal direction of one main surface of the first semiconductor layer 3. This thickness is set to, for example, 10 to 200 nm.

  The upper electrode layer 5 is a transparent conductive film provided on the second semiconductor layer 4, and is an electrode that extracts charges generated in the first semiconductor layer 3. The upper electrode layer 5 is made of a material having a lower resistivity than the second semiconductor layer 4. The upper electrode layer 5 includes what is called a window layer, and when a transparent conductive film is further provided in addition to the window layer, these may be regarded as an integrated upper electrode layer 5.

The upper electrode layer 5 mainly includes a material having a wide forbidden band, transparent, and low resistance. As such a material, for example, a metal oxide semiconductor such as ZnO, In ₂ O ₃ and SnO ₂ can be adopted. These metal oxide semiconductors may contain any element of Al, B, Ga, In, F, and the like. Specific examples of the metal oxide semiconductor containing such an element include, for example, AZO (Aluminum Zinc Oxide), GZO (Gallium Zinc Oxide),
Examples include IZO (Indium Zinc Oxide), ITO (Indium Tin Oxide), and FTO (Fluorine tin Oxide).

  The upper electrode layer 5 is formed to have a thickness of 0.05 to 3.0 μm by sputtering, vapor deposition, chemical vapor deposition (CVD), or the like. Here, from the viewpoint of good charge extraction from the first semiconductor layer 3, the upper electrode layer 5 has a resistivity of less than 1 Ω · cm and a sheet resistance of 50Ω / □ or less. Can do.

  The second semiconductor layer 4 and the upper electrode layer 5 can be made of a material having a property (also referred to as light transmittance) that allows light to easily pass through the wavelength region of light absorbed by the first semiconductor layer 3. Thereby, a decrease in light absorption efficiency in the first semiconductor layer 3 caused by providing the second semiconductor layer 4 and the upper electrode layer 5 is reduced.

In addition, from the viewpoint of improving the light transmittance, the effect of preventing loss of light reflection and the light scattering effect, and further transmitting the current generated by the photoelectric conversion, the upper electrode layer 5 can have a thickness of 0.05 to 0.5 μm. Further, from the viewpoint of reducing the light reflection loss at the interface between the upper electrode layer 5 and the second semiconductor layer 4, the absolute refractive index is substantially between the upper electrode layer 5 and the second semiconductor layer 4. It can be made the same.

  The collecting electrodes 7 are spaced apart in the Y-axis direction, and each extend in the X-axis direction. The collector electrode 7 is an electrode having conductivity, and is made of a metal such as silver (Ag), for example.

  The collecting electrode 7 plays a role of collecting charges generated in the first semiconductor layer 3 and taken out in the upper electrode layer 5. If the current collecting electrode 7 is provided, the upper electrode layer 5 can be thinned.

  The charges collected by the collector electrode 7 and the upper electrode layer 5 are transmitted to the adjacent photoelectric conversion cell 10 through the connection conductor 6 provided in the second groove portion P2. For example, the connection conductor 6 is constituted by a portion extending in the Y-axis direction of the current collecting electrode 7 as shown in FIG. Thereby, in the photoelectric conversion apparatus 11, one lower electrode layer 2 of the adjacent photoelectric conversion cell 10 and the other collector electrode 7 are electrically connected via the connection conductor 6 provided in the second groove portion P2. Connected in series. In addition, the connection conductor 6 is not limited to this, You may be comprised by the extension part of the upper electrode layer 5. FIG.

  The current collecting electrode 5 has a width of 50 to 400 μm so that good conductivity is ensured and a decrease in the light receiving area that affects the amount of light incident on the first semiconductor layer 3 is minimized. Can be.

<(2) Method for Manufacturing Photoelectric Conversion Device>
3 to 7 are cross-sectional views each schematically showing a state during the manufacture of the photoelectric conversion device 11. Each of the cross-sectional views shown in FIGS. 3 to 7 shows a state in the middle of manufacturing a portion corresponding to the cross-section shown in FIG.

  First, the lower electrode layer 2 made of Mo or the like is formed on substantially the entire surface of the cleaned substrate 1 using a sputtering method or the like. Then, the first groove portion P1 is formed from the linear formation target position along the Y direction on the upper surface of the lower electrode layer 2 to the upper surface of the substrate 1 immediately below the formation position. The first groove portion P1 can be formed, for example, by laser scribing, in which groove processing is performed by irradiating the formation target position while scanning with laser light from a YAG laser or the like. FIG. 3 is a diagram illustrating a state after the first groove portion P1 is formed.

  After forming the first groove P1, the atomic concentration ratio of the group 16 element to the group 13 element in the surface portion (surface portion opposite to the lower electrode layer 2) on the lower electrode layer 2 is larger than 2. 1 semiconductor layer 3 is formed. The group 16 element in the first semiconductor layer 3 refers to a sulfur (S) element, a selenium (Se) element, and a tellurium (Te) element excluding an oxygen (O) element (hereinafter referred to as a sulfur element). Selenium and tellurium elements are called chalcogen elements).

  The atomic concentration ratio of the group 16 element to the group 13 element in the surface portion of the first semiconductor layer 3 can be, for example, 2.1 or more and 2.5 or less. If it is such a range, the diffusion of the 12th group element mentioned later can be made more favorable.

  Such a first semiconductor layer 3 can be formed, for example, by a process called a so-called coating method or printing method. A process referred to as a coating method or a printing method is a process in which a raw material solution containing the constituent elements of the first semiconductor layer 3 is applied on the lower electrode layer 2 to form a film, and then this film is heat-treated. is there. FIG. 4 is a diagram illustrating a state after the first semiconductor layer 3 is formed.

Here, in order to obtain the first semiconductor layer 3 in which the atomic concentration ratio of the group 16 element (chalcogen element) to the group 13 element in the surface portion is larger than 2, the following raw material solution is used and the following Adopt heat treatment conditions. That is, as the raw material solution, a solution obtained by dissolving a chalcogen element in a solvent in an amount in which the atomic concentration is larger than 2 with respect to the group 13 element in addition to the group 11 element and the group 13 element is used. In addition, when a film prepared using such a raw material solution is heat-treated at a temperature of 450 to 600 ° C. to form an I-III-VI group compound, a chalcogen element is also contained in the atmosphere during the heat treatment, for example, sulfur vapor. Selenium vapor, tellurium vapor, hydrogen sulfide, hydrogen selenide or hydrogen telluride. As described above, since the chalcogen element is in an excessive state both in the raw material solution and in the heat treatment conditions, the manufactured first semiconductor layer 3 has at least a group 16 element (chalcogen element) with respect to the group 13 element in the surface portion. The atomic concentration ratio is greater than 2. In particular, the surface portion of the first semiconductor layer 3 has a high contact rate with the chalcogen element in the atmosphere during the heat treatment, and thus the ratio of the chalcogen element is likely to be higher.

  In the step of diffusing the group 12 element into the surface of the first semiconductor layer 3 to be described later, the group 12 element is mainly formed on the surface while suppressing the diffusion of the group 12 element into the first semiconductor layer 3. From the viewpoint that it becomes easier to diffuse more elements, the atomic concentration ratio of the group 16 element (chalcogen element) to the group 13 element in the surface portion of the first semiconductor layer 3 is 2.1 or more and 2.5 or less. The atomic concentration ratio of the chalcogen element to the group 13 element in the balance may be 2 or less. The first semiconductor layer 3 having a higher chalcogen element concentration in the surface portion than the remaining portion can be manufactured as follows. That is, when forming a film using a raw material solution, a raw material solution having a low chalcogen element concentration may be used for the remainder, and a high chalcogen element concentration as described above may be used for the surface portion. The thickness of the surface portion where the concentration of the chalcogen element is high may be 0.01 to 0.3 times the thickness of the entire first semiconductor layer 3.

  After forming the first semiconductor layer 3, the first semiconductor layer 3 is heated in an atmosphere containing an organometallic compound of a group 12 element so that the group 12 element is applied to the surface portion of the first semiconductor layer 3. Spread. The organometallic compound of group 12 element is a compound in which carbon of the organic compound is bonded to group 12 element. Examples of such organometallic compounds of Group 12 elements include dimethyl zinc, diethyl zinc, dipropyl zinc, dimethyl cadmium, diethyl cadmium, dipropyl cadmium and the like. From the viewpoint of reducing the environmental load, zinc (Zn) may be used as the group 12 element of the organometallic compound.

  As temperature of the 1st semiconductor layer 3 at the time of heating in the said atmosphere, it can be 150-250 degreeC. Within such a temperature range, the group 12 element can be favorably diffused in the surface portion of the first semiconductor layer 3 where the chalcogen element is excessively present, and the group 12 element is excessively diffused. Progressing to the inside of the semiconductor layer 3 can be reduced. As a result, the photoelectric conversion efficiency of the photoelectric conversion device 11 can be improved.

  Further, as the first semiconductor layer 3, the atomic concentration ratio of the group 16 element to the group 13 element in the surface portion is 2.1 or more and 2.5 or less, and the atomic concentration ratio of the group 16 element to the group 13 element in the remaining portion is In the case of using one that is 2 or less, the diffusion amount of the group 12 element to the surface portion of the first semiconductor layer 3 is increased while further suppressing the diffusion of the group 12 element into the first semiconductor layer 3. be able to. When such a first semiconductor layer 3 is used, the temperature of the first semiconductor layer 3 when heated in an atmosphere containing the organometallic compound may be 150 to 400 ° C.

  Next, the second semiconductor layer 4 and the upper electrode layer 5 are sequentially formed on the first semiconductor layer 3 in which the group 12 element is diffused.

The second semiconductor layer 4 can be formed by a solution growth method (also referred to as a CBD method). For example, indium chloride, thioacetamide, and dilute hydrochloric acid are dissolved in water to form a film-forming solution, and the substrate 1 that has been formed up to the formation of the first semiconductor layer 3 is immersed in this film-forming solution, whereby the first A second semiconductor layer 4 containing In ₂ S ₃ can be formed on the semiconductor layer 3.

  When the second semiconductor layer 4 is formed by the CBD method, if the oxide layer 3a can be dissolved by the film formation liquid used for the CBD method, the removal of the oxide layer 3a and the second semiconductor layer 4 are the same. You may perform simultaneously using a film-forming liquid. In that case, the manufacturing process can be simplified.

  The upper electrode layer 5 is a transparent conductive film containing, for example, indium oxide (ITO) containing Sn as a main component, and can be formed by a sputtering method, a vapor deposition method, a CVD method, or the like. FIG. 5 is a diagram showing a state after the second semiconductor layer 4 and the upper electrode layer 5 are formed.

  After the upper electrode layer 5 is formed, the second groove portion P2 is formed from the linear formation target position along the Y direction on the upper surface of the upper electrode layer 5 to the upper surface of the lower electrode layer 2 immediately below it. The second groove portion P2 can be formed by, for example, mechanical scribing using a scribe needle. FIG. 6 is a diagram illustrating a state after the second groove portion P2 is formed. The second groove portion P2 is formed at a position slightly deviated in the X direction (+ X direction in the drawing) from the first groove portion P1.

  After forming the second groove P2, the current collecting electrode 7 and the connection conductor 6 are formed. For the collector electrode 7 and the connection conductor 6, for example, a conductive paste (also referred to as a conductive paste) in which a metal powder such as Ag is dispersed in a resin binder or the like is printed so as to draw a desired pattern. It can be formed by heating. FIG. 7 is a view showing a state after the current collecting electrode 7 and the connection conductor 6 are formed.

  After forming the current collection electrode 7 and the connection conductor 6, the 3rd groove part P3 is formed from the linear formation object position of the upper surface of the upper electrode layer 5 to the upper surface of the lower electrode layer 2 just under it. The width | variety of the 3rd groove part P3 can be about 40-1000 micrometers, for example. Moreover, the 3rd groove part P3 can be formed by a mechanical scribing process similarly to the 2nd groove part P2. In this way, the photoelectric conversion device 11 shown in FIGS. 1 and 2 is manufactured by forming the third groove portion P3.

1: Substrate 2: First electrode layer 3: First semiconductor layer 4: Second semiconductor layer 5: Second electrode layer 10: Photoelectric conversion cell 11: Photoelectric conversion device

Claims (5)

A light-absorbing layer that mainly contains a chalcopyrite compound containing a group 11 element, a group 13 element, and a group 16 element and has an atomic concentration ratio of the group 16 element to the group 13 element in the surface portion on the main surface side larger than 2 is prepared. And a process of
Heating the light absorbing layer in an atmosphere containing an organometallic compound of a group 12 element and diffusing the group 12 element in the surface portion.   2. The method for manufacturing a photoelectric conversion device according to claim 1, wherein the light absorption layer has an atomic concentration ratio of 2.1 to 2.5 in the surface portion.   3. The method for manufacturing a photoelectric conversion device according to claim 2, wherein the light absorption layer is one having an atomic concentration ratio of 2 or less in the remaining portion of the first semiconductor layer.   The method for manufacturing a photoelectric conversion device according to claim 1, wherein Zn is used as a group 12 element.   The method for manufacturing a photoelectric conversion device according to any one of claims 1 to 4, wherein Cu is used as the Group 11 element, at least one of In and Ga is used as the Group 13 element, and Se is used as the Group 16 element.

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