JP2015185629A - Method of manufacturing photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion device that is further enhanced in photoelectric conversion efficiency.SOLUTION: A method of manufacturing a photoelectric conversion device 11 comprises a first step of preparing a buffer layer 4 containing metal sulfide on a light absorption layer 3 containing metal chalcogenide with acidic first solution, and a second step of bringing acidic second solution containing an alkali metal compound and a thioamide-based compound or thiourea-based compound on the surface of the buffer layer 4.

Description

  The present invention relates to a method for manufacturing a photoelectric conversion device using a semiconductor containing a metal chalcogenide as a light absorption layer.

As a photoelectric conversion device used for solar power generation or the like, there is one using a semiconductor containing a metal chalcogenide as a light absorption layer. As such metal chalcogenides, I-III-VI group compounds such as CIS and CIGS, or I-II-IV-VI group compounds such as CZTS are used (see Patent Document 1 and Patent Document 2). .

Such a photoelectric conversion device has a lower electrode layer such as a metal electrode, a light absorption layer, a buffer layer containing ZnS or In ₂ S ₃ , a transparent electrode, a metal electrode, or the like on a substrate such as glass. The upper electrode layers are stacked in this order.

  And in order to improve the photoelectric conversion efficiency of a photoelectric conversion apparatus, in patent document 3, after preparation of a buffer layer, the alkali metal solution is made to contact the surface of this buffer layer. By such a method, defects present at the interface between the light absorption layer and the buffer layer can be filled with alkali metal atoms, and the photoelectric conversion efficiency can be improved.

JP 2000-299486 A JP 2007-269589 A International Publication No. 2013/157321

  In solar power generation, it is always required to obtain more power in a limited space. Then, this invention aims at the further improvement of the photoelectric conversion efficiency in a photoelectric conversion apparatus.

  A method for manufacturing a photoelectric conversion device according to an embodiment of the present invention includes a first step of producing a buffer layer containing a metal sulfide using a first acidic solution on a light absorption layer containing a metal chalcogenide, and the buffer. And a second step of contacting the surface of the layer with an acidic second solution containing an alkali metal compound and a thioamide compound or a thiourea compound.

  According to the embodiment of the present invention, a photoelectric conversion device with high photoelectric conversion efficiency can be provided.

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

  Hereinafter, an embodiment of the present invention will be described in detail 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 and positional relationships 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 8 are attached 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 includes a large number of photoelectric conversions in the X-axis direction of the drawing or further in the Y-axis direction of the drawing. The cells 10 are arranged in a plane (two-dimensionally).

  Each photoelectric conversion cell 10 mainly includes a lower electrode layer 2, a light absorption layer 3, a buffer 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. As a specific example, for example, blue plate glass (soda lime glass) having a thickness of about 1 to 3 mm may be used as the substrate 1.

  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 light absorption layer 3 is a semiconductor layer that absorbs light and performs photoelectric conversion. The light absorption layer 3 has the first conductivity type (here, p-type conductivity type), and has a thickness of, for example, about 1 to 3 μm on the main surface on the + Z side of the lower electrode layer 2. Is provided. The light absorption layer 3 mainly contains metal chalcogenide. Note that the phrase “mainly containing metal chalcogenide” means containing metal chalcogenide in an amount of 70 mol% or more.

  A metal chalcogenide is a compound of a metal element and a chalcogen element. The chalcogen element refers to sulfur (S), selenium (Se), and tellurium (Te) among group 16 elements (also referred to as group VI-B elements). Metal chalcogenides include group 11 elements (also referred to as group IB elements), group 13 elements (also referred to as group III-B elements) and group 16 elements, group III-VI compounds, group 11 elements. I-II-IV-VI group compounds and 12-group elements and 16-group elements (also referred to as II-B group elements), 14-group elements (also referred to as IV-B group elements) and 16-group elements II-VI group compounds that are compounds with group elements can be employed.

Examples of the I-III-VI group compound include CuInSe ₂ (indium diselenide,
CIS), Cu (In, Ga) Se ₂ (also called copper indium gallium selenide, CIGS), Cu (In, Ga) (Se, S) ₂ (diselen copper indium gallium indium gallium, CIGSS). In addition, the light absorption layer 3 may be a multi-layered laminate, and may be configured by, for example, a CIGS layer having a thin CIGSS layer as a surface layer.

Examples of the I-II-IV-VI group compound include Cu ₂ ZnSnS ₄ (also referred to as CZTS), Cu ₂ ZnSn (S, Se) ₄ (also referred to as CZTSSe), and Cu ₂ ZnSnSe ₄ (also referred to as CZTSe). Can be mentioned. Moreover, as a II-VI group compound, CdTe etc. are mentioned, for example.

The buffer layer 4 is a semiconductor layer having a thickness of about 3 to 200 nm that is heterojunction with the light absorption layer 3. The buffer layer 4 contains a metal sulfide and is produced using an acidic solution. Examples of the metal sulfide include indium sulfide (In ₂ S ₃ ), cadmium sulfide (CdS), and zinc sulfide (ZnS). The buffer layer 4 may contain a metal oxide, a metal hydroxide, or the like in addition to the metal sulfide. From the viewpoint of improving band matching with the light absorption layer 3 containing metal chalcogenide, the buffer layer 4 may contain 20 mol% or more of metal sulfide.

  The upper electrode layer 5 is a transparent conductive film having a second conductivity type (here, n-type conductivity type) provided on the buffer layer 4, and is an electrode for extracting charges generated in the light absorption layer 3. is there. The upper electrode layer 5 is made of a material having an electrical resistivity lower than that of the buffer 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 elements such as Al, B, Ga, In, Sn, Sb, and F. Specific examples of the metal oxide semiconductor containing such an element include, for example, AZO (Aluminum Zinc Oxide), BZO (boron zinc oxide), and GZ.
O (Gallium Zinc Oxide), 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 μm by sputtering, vapor deposition, chemical vapor deposition (CVD), or the like. Here, from the viewpoint of good charge extraction from the light absorption layer 3, the upper electrode layer 5 can have a resistivity of 1 Ω · cm or less and a sheet resistance of 50 Ω / □ or less. .

  Further, from the viewpoint of improving the light transmittance and at the same time, transmitting the current generated by the photoelectric conversion well, the upper electrode layer 5 should have a thickness of 0.05 to 0.5 μm. it can.

  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 light absorption 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, as shown in FIG. 2, the connection conductor 6 is configured by a portion of the current collecting electrode 7 extending in the Y-axis direction. 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 reduction in the light receiving area that affects the amount of light incident on the light absorbing layer 3 is minimized. can do.

<(2) Method for Manufacturing Photoelectric Conversion Device>
3 to 8 are cross-sectional views schematically showing a state during the manufacture of the photoelectric conversion device 11. Each of the cross-sectional views shown in FIGS. 3 to 8 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 by, for example, a scribe process in which a groove process is performed by irradiating a formation target position while scanning with a laser beam such as a YAG laser. FIG. 3 is a diagram illustrating a state after the first groove portion P1 is formed.

  After forming the first groove P1, the light absorption layer 3 is formed on the lower electrode layer 2. The light absorption layer 3 can be formed by a so-called vacuum process such as a sputtering method or a vapor deposition method, or can be formed by a process called a coating method or a printing method. A process referred to as a coating method or a printing method is a process in which a complex solution of constituent elements of the light absorption layer 3 is applied on the lower electrode layer 2 and then dried and heat-treated. FIG. 4 is a diagram illustrating a state after the light absorption layer 3 is formed.

  After forming the light absorption layer 3, the buffer layer 4 containing a metal sulfide is formed on the light absorption layer 3 using an acidic first solution. FIG. 5 is a diagram illustrating a state after the buffer layer 4 is formed.

The method of forming the buffer layer 4 using the first solution is a method in which the buffer layer 4 is deposited on the light absorbing layer 3 by bringing the first solution containing the metal sulfide raw material into contact with the light absorbing layer 3. is there. As a specific example of such a method, the substrate 1 on which the light absorption layer 3 is formed is immersed in the first solution containing the raw material of the buffer layer 4, and the buffer layer 4 is deposited on the light absorption layer 3. Chemical
There is a method called a bath deposition method (CBD method). The term “immersion” means immersion in a liquid.

  The acidic first solution used in the CBD method includes a metal compound such as a metal salt or a metal complex, a sulfur compound such as a thioamide compound or a thiourea compound, an acid such as hydrochloric acid, and a solvent such as water or alcohol. It is dissolved in The first solution being acidic means that the pH is in the range of 1 to 6 if the solvent of the first solution is water.

As a specific example of the CBD method, for example, the substrate 1 that has been subjected to the formation of the light absorption layer 3 is immersed in an aqueous solution or alcohol solution in which indium chloride, thioacetamide, and hydrochloric acid are dissolved. A buffer layer 4 containing In ₂ S ₃ can be formed thereon.

  After the buffer layer 4 is formed, an acidic second solution containing an alkali metal compound and containing a thioamide compound or a thiourea compound is brought into contact with the surface of the buffer layer 4.

Here, the alkali metal compound is a compound of an alkali metal element and refers to a substance that can be ionized to an alkali metal ion in a solvent of the second solution (polar solvent such as water or alcohol). As the alkali metal element, Li, Na, K, Rb, or Cs can be used among Group 1 (also referred to as Group IA) of the periodic table. As such an alkali metal compound, for example, NaCl, NaNO ₃ , NaClO ₄ , Na ₂ S, NaOH, KCl, KNO ₃ , NaClO ₄ , K ₂ S, KOH or the like can be used. The concentration of the alkali metal compound in the second solution is, for example, 1 to 500 mol / m ³ .

A thioamide compound is an organic compound having a thioamide group. A thiourea compound is a derivative in which part or all of hydrogen in thiourea or thiourea is substituted with an organic group. As such a thioamide compound, for example, thioacetamide, thioformamide and the like can be used. Moreover, as a thiourea type compound, thiourea, diethylthiourea, etc. can be used, for example. The concentration of the thioamide compound or thiourea compound in the second solution is, for example, 1 to 2000 mol / m ³ .

  The second solution is an acidic solution by adding hydrochloric acid, nitric acid or the like. The second solution being acidic means that the pH is in the range of 1 to 6 if the solvent of the second solution is water.

  The step of bringing the second solution into contact with the surface of the buffer layer 4 may be, for example, a step of immersing the substrate 1 on which the buffer layer 4 is formed in the second solution (also referred to as a dip treatment step), Alternatively, it may be a step of applying the second solution to the surface of the buffer layer 4. Hereinafter, the step of immersing the substrate 1 on which the buffer layer 4 is formed in the second solution is referred to as a “contacting step by immersion” and is a step of applying the second solution to the surface of the buffer layer 4. Is referred to as “contact process by coating”.

  When using the “contact process by immersion”, the temperature of the second solution may be, for example, 20 to 80 ° C. Further, the time for immersing the substrate 1 in the second solution may be, for example, 1 to 60 minutes.

  Moreover, when using the “contact process by coating”, the temperature of the substrate 1 may be set to, for example, 50 to 250 ° C. to perform the contact process. Moreover, after performing the contact process by application | coating, in order to remove the unreacted substance and by-product which remain | survived in the buffer layer 4, you may wash | clean the buffer layer 4 with water etc.

  After preparing the buffer layer 4 on the light absorption layer 3 in this manner, the buffer layer 4 is brought into contact with a second solution containing an alkali metal compound, thereby electrically connecting the light absorption layer 3 and the buffer layer 4. Can be good. That is, by joining the light absorption layer 3 and the buffer layer 4 first, heterojunction of these two types of semiconductor layers can be performed well, and then the light absorption layer 3 and the buffer layer 4 are formed by the second solution. Can be satisfactorily filled with an alkali metal element. Further, the presence of the alkali metal element at the interface between the light absorption layer 3 and the buffer layer 4 increases the carrier concentration.

Furthermore, the second solution is an acidic solution not only containing an alkali metal compound but also containing a thioamide compound or a thiourea compound. Therefore, by bringing the second acid solution made in the same manner into contact with the buffer layer 4 manufactured using the acidic first solution, the surface state of the buffer layer 4 is not greatly changed. Processing can be performed satisfactorily. Moreover, compared with the case where an acidic solution containing an alkali metal compound is brought into contact with the buffer layer 4, the solubility of the buffer layer 4 in the second solution is reduced by further including a thioamide compound or a thiourea compound. The state of the buffer layer 4 can be maintained well. As a result, the photoelectric conversion efficiency of the photoelectric conversion device 11 can be improved.

  After bringing the second solution into contact with the surface of the buffer layer 4 as described above, the light absorption layer 3 and the buffer layer 4 may be further annealed at 100 to 250 ° C., for example. This annealing time may be, for example, 10 to 180 minutes. By performing such an annealing step, the photoelectric conversion efficiency is further increased.

  Note that the atmosphere in this annealing step may be an atmosphere containing hydrogen. This further improves the photoelectric conversion efficiency. Note that as the atmosphere containing hydrogen, a hydrogen atmosphere or a mixed atmosphere containing hydrogen and an inert gas can be used. When a mixed atmosphere is used, nitrogen or argon can be used as the inert gas, and the hydrogen content in the mixed atmosphere can be 50 mol% or more.

  After the buffer layer 4 is processed as described above, the upper electrode layer 5 is formed on the buffer layer 4. The upper electrode layer 5 is a transparent conductive film containing, for example, ITO or AZO as a main component, and can be formed by a sputtering method, a vapor deposition method, a CVD method, or the like. FIG. 6 is a view showing a state after the upper electrode layer 5 is 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, for example, by performing scribing using a scribe needle having a scribe width of about 40 to 50 μm continuously several times while shifting the repetition interval. Alternatively, the second groove portion P2 may be formed by scribing after the tip shape of the scribe needle is expanded to an extent close to the width of the second groove portion P2. Alternatively, the second groove portion P2 may be formed by fixing two or more than two scribe needles in contact with or in close proximity to each other and performing scribing from one to several times. FIG. 7 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) formed by dispersing a metal powder such as Ag in a resin binder or the like is printed so as to draw a desired pattern, This can be formed by heating. FIG. 8 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 of the third groove P3 may be about 40 to 1000 μm, for example. Moreover, what is necessary is just to form the 3rd groove part P3 by mechanical scribing similarly to the 2nd groove part P2. In this manner, the photoelectric conversion device 11 shown in FIGS. 1 and 2 is manufactured by forming the third groove portion P3.

  The present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the scope of the present invention.

  Next, a method for manufacturing the photoelectric conversion device 11 will be described with a specific example.

<Preparation of sample for evaluation>
First, a raw material solution for forming a light absorption layer was prepared. As the raw material solution, a solution obtained by dissolving a single source precursor prepared in accordance with the description of US Pat. No. 6,992,202 in pyridine was used. In addition, as this single source precursor, Cu, In, and phenyl selenol formed one complex molecule, and Cu, Ga, and phenyl selenol formed one complex molecule. Using the body.

  Next, a plurality of substrates having a lower electrode layer made of Mo are prepared on the surface of the substrate 1 made of glass, and a raw material solution is applied onto the lower electrode layer by a blade method to form a film. Formed.

  Next, this film was heated at 550 ° C. for 1 hour in an atmosphere in which hydrogen gas contained selenium vapor in a partial pressure ratio of 20 ppmv to form a light absorption layer mainly containing CIGS and having a thickness of 2 μm.

Next, each substrate on which the light absorption layer is formed is immersed in an aqueous solution prepared by dissolving 17 mol / m ³ of indium chloride and 68 mol / m ³ of thioacetamide and adjusting the pH to 2.5 with hydrochloric acid. A buffer layer containing In ₂ S ₃ having a thickness of 17.5 nm was formed on the light absorption layer.

  Then, different treatments under the three conditions shown in Table 1 were performed on each of the substrates on which the buffer layers were formed. In addition, pH of the treatment solution used for each sample was adjusted with hydrochloric acid.

  Specifically, the substrate on which the layers up to the buffer layer were formed was immersed in each evaluation solution shown in Table 1 (both the liquid temperature was 70 ° C.) for 30 minutes. Sample 3 is a sample that has not been immersed in the evaluation solution.

  Thereafter, an upper electrode layer made of ZnO doped with Al was formed on each of the buffer layers of Samples 1 to 3 to form three types of photoelectric conversion devices.

<Evaluation of sample>
With respect to Samples 1 to 3 thus produced, each cross section before and after immersion in the evaluation solution was observed using a scanning electron microscope (SEM), and the film thickness of the buffer layer was measured. The results are shown in Table 1.

From Table 1, it was found that the buffer layer was dissolved by immersing Sample 2 in the evaluation solution, and the film thickness of the buffer layer was reduced. On the other hand, Sample 1 was found to have little change in the film thickness of the buffer layer before and after immersion in the evaluation solution. That is, although each evaluation solution used for sample 1 and sample 2 has the same pH, it is considered that dissolution of the buffer layer can be reduced by further adding thioacetamide.

Next, the photoelectric conversion efficiency of Samples 1 to 3 was measured as follows. Using a so-called steady light solar simulator, the photoelectric conversion efficiencies of samples 1 to 3 under the condition that the light irradiation intensity on the light receiving surface of the photoelectric conversion device is 100 mW / cm ² and AM (air mass) is 1.5. It was measured. The results are shown in Table 1.

  From Table 1, it was found that sample 2 immersed in an acidic evaluation solution containing NaCl but not containing thioacetamide had a lower photoelectric conversion efficiency than sample 3 not immersed in the evaluation solution. This is presumably because the buffer layer was dissolved in the sample 2 by the evaluation solution and the state of the buffer layer changed from the result of the change in the thickness of the buffer layer. On the other hand, it was found that Sample 1 immersed in an acidic evaluation solution containing NaCl and thioacetamide had higher photoelectric conversion efficiency than Sample 2 and Sample 3. That is, it is considered that the sample 1 has a good buffer layer state by further containing thioacetamide, and has a higher photoelectric conversion efficiency by further containing Na, which is an alkali metal.

1: Substrate 2: Lower electrode layer 3: Light absorption layer 4: Buffer layer 5: Upper electrode layer 6: Connection conductor 7: Current collecting electrode 10: Photoelectric conversion cell 11: Photoelectric conversion device

Claims (5)

A first step of producing a buffer layer containing a metal sulfide using an acidic first solution on a light absorbing layer containing a metal chalcogenide;
And a second step of contacting the surface of the buffer layer with an acidic second solution containing an alkali metal compound and a thioamide compound or a thiourea compound.   The method for manufacturing a photoelectric conversion device according to claim 1, wherein the second step is a step of immersing the buffer layer in the second solution.   The method for manufacturing a photoelectric conversion device according to claim 1, wherein the second step is a step of applying the second solution onto the buffer layer.   The method for manufacturing a photoelectric conversion device according to claim 1, further comprising an annealing step of annealing the light absorption layer and the buffer layer after the second step.   The method for manufacturing a photoelectric conversion device according to claim 4, wherein the annealing step is performed in an atmosphere containing hydrogen.