JP2014017426A - Photoelectric conversion device and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve a problem occurring when forming a light absorption layer of a compound thin film solar cell such as a chalcopyrite type and a kesterite type by sulfurizing or seleniding the light absorption layer from a precursor that a compression stress associated with volume expansion occurs in the precursor and sometimes peeling from an underlayer occurs thereby to manufacture the light absorption layer having a good film quality while inhibiting peeling.SOLUTION: A photoelectric conversion device manufacturing method comprises a process of forming a precursor including two and more kinds of metal elements and oxygen within a range of 25 atom%-60 atom%, and subsequently forming a light absorption layer by performing a sulfuration treatment on the precursor.

Description

  The present invention relates to a compound photoelectric conversion device, and more particularly to a thin film type compound photoelectric conversion device.

  In compound photoelectric conversion devices, compound light absorption layers such as CuInS2 (CIS), Cu (In, Ga) Se2 (CIGS), Cu2ZnSnS4 (CZTS), etc. are once subjected to selenization and sulfidation treatment after forming an alloy precursor thin film. A method called a step method or a three-step method is employed (Patent Document 1).

  However, when the alloy precursor thin film is selenized or sulfided, about 50 atomic% of selenium or sulfur atoms are taken in, so the alloy precursor thin film expands in volume. Since this volume expansion expands not only in the film thickness direction but also in the in-plane direction, the completed light absorption layer is subjected to compressive stress.

  When the compressive stress is increased to the degree of adhesion between the light absorption layer and the base layer such as a metal electrode, peeling at the interface occurs, which has a problem of adversely affecting device characteristics and productivity.

  As an improvement measure, there is a method of optimizing the temperature and time of selenization or sulfidation treatment. However, this method cannot sufficiently optimize selenization, sulfurization reaction, crystallization, and the like in order to suppress the compressive stress of the light absorption layer.

JP 2012-59847 A

  The problem to be solved is that when the light absorbing layer is sulfided or selenized from the precursor to produce the light absorbing layer of the chalcopyrite compound thin film solar cell, the precursor generates compressive stress along with the volume expansion. Is to cause peeling from the underlayer, and it is a problem to create a light-absorbing layer having good film quality while suppressing peeling.

  In the method for manufacturing a photoelectric conversion device according to the present invention, after a precursor containing two or more kinds of metal elements and oxygen in a range of 25 atomic% to 60 atomic% is formed, the precursor is subjected to sulfurization treatment to absorb light. Creating a layer. If oxygen atoms are added to the precursor, the desorption of oxygen and sulfidation proceed almost simultaneously during the sulfidation treatment, so that sulfidation can be promoted while suppressing volume expansion of the film. If the amount of oxygen added is 25 atomic% or more, the volume expansion suppressing effect may be sufficiently obtained. However, if the oxygen addition concentration is 60 atomic% or more, oxygen remains undesirably during sulfidation. Further, oxygen atoms may be uniformly dispersed inside the precursor film, or may have a concentration distribution in the thickness direction. However, an extremely in-plane concentration distribution is not preferable because the compressive stress due to volume expansion during the sulfiding treatment cannot be sufficiently relaxed.

  In the method for manufacturing a photoelectric conversion device according to the present invention, the precursor before the sulfiding treatment is amorphous. If the precursor is amorphous, it is sufficient that there are few things that prevent the sulfidation reaction and the crystal growth of the sulfide in the subsequent sulfidation treatment. In addition, it can be confirmed that the precursor is amorphous by a diffraction peak not appearing by an X-ray diffraction method by the θ-2θ method. In addition, even if a peak appears, one having a half width of 5 ° or more is regarded as amorphous.

  In the method for manufacturing a photoelectric conversion device according to the present invention, the precursor includes at least one of copper, silver, and iron and at least one metal element of zinc, aluminum, and indium. Specifically, combinations of copper-zinc-tin, copper-indium, copper-aluminum, silver-zinc-tin, silver-indium, silver-aluminum, iron-zinc-tin, iron-indium, iron-aluminum, etc. Examples thereof include, but are not limited to, those capable of forming chalcopyrite-type and kesterite-type compounds by selenization or sulfuration treatment.

  In the method for manufacturing a photoelectric conversion device according to the present invention, the precursor is formed by a reactive sputtering method using oxygen as a reactive gas. As a target, a multi-component alloy or sintered metal prepared at a desired composition ratio may be used, or a film having a desired composition ratio is prepared by charging each element into an individual sputtering source and controlling the sputtering power ratio or the like. You may adjust it. It is preferable to introduce oxygen while adjusting the introduction amount so that a desired film composition can be obtained in consideration of sputtering power, target size, sputtering pressure, and the like. In addition, when the amount of oxygen introduced is large, arcing may occur due to oxidation of the target surface, or the discharge may be stopped. Therefore, a power application method such as pulse application or high-frequency sputtering may be appropriately selected.

  In the method for producing a photoelectric conversion device according to the present invention, the precursor is heated to 350 ° C. for 30 minutes or more in an atmosphere in which sulfur element exists, and is subjected to sulfurization treatment. As an atmosphere in which sulfur element exists, sulfur powder may be placed in a quartz tube and heated, or hydrogen sulfide, carbon disulfide, or the like may be appropriately introduced. When the heating temperature is set to 350 ° C. or higher, both oxygen desorption and sulfurization from the precursor may occur. Further, if the heating time is set to 30 minutes or longer at 350 ° C. or higher, it is easy to ensure crystallinity such as chalcopyrite structure and kesterite structure. Further, if it is 550 ° C. or higher, the crystallite size can be easily increased. However, if the temperature is 600 ° C. or higher, the type of glass that can be used as the base material is limited.

  The photoelectric conversion device according to the present invention has a light absorption layer formed by any of the processes described above. The photoelectric conversion device according to the present invention may have a superstrate structure in which the light absorption layer is formed on the base layer having the transparent conductive film, or any of the substrate structures formed on the base layer having the metal electrode. good.

  In the method for manufacturing a photoelectric conversion device according to the present invention, when oxygen atoms are added to the precursor, oxygen desorption and sulfidation proceed at almost the same time during sulfidation, thereby suppressing the volume expansion of the film. Can be promoted.

It is explanatory drawing which showed the composition ratio of the precursor. Example 1 It is explanatory drawing which showed the ratio of the metal element of a precursor. Example 1 It is explanatory drawing which showed the crystal structure of the precursor. Example 1 It is explanatory drawing which showed the crystal structure of the light absorption layer. (Example 2) It is explanatory drawing which showed the composition ratio of the light absorption layer. (Example 2) It is explanatory drawing which showed the ratio of the metal element of a light absorption layer. (Example 2) It is explanatory drawing which showed the surface photograph of the light absorption layer. (Example 2) It is explanatory drawing which showed the cross-sectional photograph of the light absorption layer. (Example 2) It is explanatory drawing which showed the surface photograph of the light absorption layer. (Example 2) It is explanatory drawing which showed the cross-sectional photograph of the light absorption layer. (Example 2) It is explanatory drawing which showed the surface photograph of the light absorption layer. (Example 2)

  Hereinafter, an example of an embodiment for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited to this. The method for producing a photoelectric conversion device of the present invention can be broadly divided into a step of forming a precursor thin film and a step of sulfiding it.

First, a molybdenum film was formed as a metal electrode layer on a glass substrate by a sputtering method. A 20 mm square and 1 mm thick soda lime glass (manufactured by Matsunami Glass Industry Co., Ltd.) was used for the substrate. A molybdenum target having a diameter of 150 mm, a thickness of 5 mm, and a purity of 99.95% (manufactured by Furuuchi Chemical Co., Ltd.) was used. The sputter apparatus was loaded with a cleaned glass substrate and a molybdenum target, and the inside of the chamber was evacuated to 4 × 10 ⁻⁴ Pa or lower, and then argon gas with a purity of 99.999% or higher was introduced and adjusted to 1.0 Pa. Next, high frequency power 410W of 13.56 MHz was input to the sputter cathode, and the impedance of the matching box was adjusted to set the reflected power to 0 W. In this state, pre-sputtering was performed for 30 minutes with the shutter between the substrate and the target closed. Next, the shutter was opened and a film of molybdenum was formed on the substrate surface for 14 minutes and 30 seconds. Then, the inside of the chamber was returned to atmospheric pressure, and the substrate with molybdenum was taken out. The substrate was not intentionally heated. The film thickness of the formed molybdenum film was 0.8 μm as observed by cross-sectional SEM.

Next, in another sputtering device, a precursor alloy target with a diameter of 51 mm, a thickness of 5 mm, and a purity of 99.9% or more, prepared by mixing the glass substrate with molybdenum and copper, zinc, and tin in a 2: 1: 1 atomic ratio ((Co., Ltd. ) High purity chemical laboratory). Next, after evacuating the inside of the chamber to 1 × 10 ⁻⁴ Pa or less, oxygen with a purity of 99.999% or more is introduced under any of 0 SCCM, 0.3SCCM, 0.5SCCM, or 0.6SCCM, and then argon with a purity of 99.999% or more is introduced. Gas was introduced and the pressure was adjusted to 0.6 Pa. The oxygen partial pressure at this time is 0%, 5%, 17%, and 20%. Next, 80 W of high frequency power of 13.56 MHz was input to the sputter cathode, and the impedance of the matching box was adjusted so that the reflected power was 0 W. In this state, pre-sputtering was performed for 20 minutes with the shutter between the substrate and target closed, and then the shutter was opened to form a precursor film for 40 minutes. The substrate was not intentionally heated. The thickness of the deposited precursor film was observed by a cross-sectional SEM, and was about 1 μm under any of the above conditions.

  Next, FIG. 1 shows the result of evaluating the composition ratio of the prepared precursor film using an energy dispersive X-ray spectrometer (EDS). The electron acceleration voltage was 20 kV. As described above, even when oxygen is not intentionally added, 8 atomic% of oxygen is detected from the precursor film. This is because the residual gas in the sputtering chamber is taken in at the time of film formation or after film formation. It is thought that it was adsorbed on the surface in the atmosphere. On the other hand, when oxygen partial pressures of 5%, 17%, and 20% are introduced into the sputtering atmosphere, it can be seen that 37 atom%, 46 atom%, and 54 atom% of oxygen atoms are introduced, respectively.

  FIG. 2 shows the element ratio of each metal shown in FIG. As described above, the Cu / Sn ratio and the Cu / (Zn + Sn) ratio slightly increased and the Zn / Metal ratio and the Zn / Sn ratio slightly decreased with increasing oxygen addition amount. Metal is the sum of atomic concentrations of Cu, Zn, and Sn. The change in the ratio of each metal element due to the addition of oxygen is considered to be caused by the difference in the sputtering rate of each metal element with respect to argon and oxygen.

  Next, FIG. 3 shows the results of examining the crystal structure of the precursor film formed on the molybdenum film under each condition by the X-ray diffraction method by the θ-2θ method. The target material of the X-ray tube is copper, and the output is 45 kV and 40 mA. The wavelength of the X-ray (K-α1) is 0.154060 nm. In addition, the peaks observed when 2θ is around 41 ° and around 73 ° are attributed to molybdenum. In this way, when oxygen is not intentionally added, multiple peaks due to the precursor constituent metal elements are seen, whereas oxygen is introduced into the sputtering atmosphere by 5% or more, and oxygen of 37 atomic% or more is introduced into the precursor film. In the case where atoms are added, no peak due to the precursor film is observed, and it can be seen that the film is amorphous. That is, it can be seen that oxygen atoms are effectively introduced into the precursor film.

  Next, the precursor prepared under each condition of Example 1 was sulfided under the following conditions to prepare a light absorption layer. First, a substrate with a precursor film and 45 mg of sulfur powder placed in a quartz tube is set in a table lamp heating device (MILA-5000 manufactured by ULVAC-RIKO Co., Ltd.), and the inside of the quartz tube is evacuated to 10 Pa or less. While flowing 99.999% or more of argon gas, the temperature was increased at 530 ° C./min, held at 550 ° C. for 30 minutes, and then decreased at 10 ° C./min.

FIG. 4 shows the results of examining the crystal structure of the light absorption layer obtained by sulfiding each precursor film prepared in Example 1 by the X-ray diffraction method using the θ-2θ method. The target material of the X-ray tube is copper, and the output is 45 kV and 40 mA. The wavelength of the X-ray (K-α1) is 0.154060 nm. In addition, the peaks observed when 2θ is around 41 ° and around 73 ° are attributed to molybdenum. Thus, diffraction from the (112) plane, (200) plane, (220/240) plane, (116/312) plane, (400) plane, (332) plane of Cu ₂ ZnSnS ₄ from any film A peak is seen, and the influence of oxygen addition at the time of precursor film formation is not seen.

Next, the result of having evaluated the composition ratio of the produced light absorption layer film | membrane using the energy dispersive X-ray spectrometer (EDS) is shown in FIG. The electron acceleration voltage was 20 kV. Thus, it can be seen that the oxygen atom concentration detected from the light absorption layer is 3 atomic% or less regardless of the addition of oxygen during the precursor film formation. That is, it can be seen that most of the oxygen atoms in the precursor are desorbed during the sulfiding treatment. In addition, it can be seen that the composition ratio of the light absorption layer obtained by the sulfiding treatment is not greatly different regardless of the oxygen atom concentration in the precursor.

  Next, the ratio of elements other than oxygen in the light absorption layer shown in FIG. 5 is shown in FIG. Thus, it can be seen that the amount of oxygen added in the precursor film hardly affects the composition ratio of the light absorption layer.

  Next, FIG. 7 shows a surface SEM photograph of the light absorption layer obtained by sulfidizing the precursor film formed by introducing 20% oxygen (54 atomic% in the precursor film) into the sputtering film formation atmosphere. The electron acceleration voltage during SEM observation is 5 kV. Thus, it can be seen that the film surface is flat.

  FIG. 8 shows a cross-sectional enlarged SEM photograph of the same sample as FIG. The bottom of the photo is a part of the molybdenum electrode. It can be seen that relatively large crystal grains have grown on it.

  FIG. 9 shows a surface SEM photograph of a light absorption layer prepared by sulfiding a precursor film prepared without intentionally adding oxygen. Thus, the surface has irregularities, and it can be seen that a part of the film is peeled off.

  FIG. 10 shows a cross-sectional enlarged SEM photograph of the same sample as FIG. Thus, it can be seen that a part of the film peels off from the molybdenum interface and expands into a dome shape. This is due to the in-plane compressive stress accompanying the volume expansion of the precursor during sulfidation. On the other hand, the same dome-shaped exfoliation was not observed in FIG. 8 because the oxygen previously added to the precursor film was released, so that a space for sulfur atoms to be taken into the film during sulfidation was secured. This is because the effectiveness of the present invention can be confirmed.

  FIG. 11 shows surface SEM photographs of a light absorption layer prepared by sulfiding a precursor film prepared under various oxygen addition conditions. Thus, dome-shaped peeling is observed only when oxygen is not intentionally added.

  High-quality compound thin-film photoelectric conversion device that can produce a good light-absorbing layer because the crystal can be sufficiently grown while suppressing the compressive stress and exfoliation caused by the volume expansion of the precursor in the sulfidation or selenization process Is easy to manufacture.

Claims (6)

  It has a step of forming a light absorption layer by forming a precursor containing two or more kinds of metal elements and oxygen in a range of 25 atomic% to 60 atomic%, and then sulfiding the precursor. The manufacturing method of a photoelectric conversion apparatus.   The method for manufacturing a photoelectric conversion device according to claim 1, wherein the precursor before the sulfiding treatment is amorphous.   3. The photoelectric conversion device according to claim 1, wherein the precursor includes at least one of copper, silver, and iron and at least one metal element of zinc, aluminum, and indium. Production method.   The method for producing a photoelectric conversion device according to claim 1, wherein the precursor is formed by a reactive sputtering method using oxygen as a reactive gas.   The method for producing a photoelectric conversion device according to any one of claims 1 to 4, wherein the precursor is subjected to sulfurization treatment by heating at 350 ° C or more for 30 minutes or more in an atmosphere containing sulfur element. It has a light absorption layer produced by the process in any one of Claims 1-5, The photoelectric conversion apparatus characterized by the above-mentioned.