JP2012204482A - Photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve conversion efficiency of a photoelectric conversion device.SOLUTION: A photoelectric conversion device 31 comprises: a light absorbing layer 3 containing a Group I-III-VI compound having a chalcopyrite structure; an intermediate layer 4 which is positioned on the light absorbing layer 3 and contains a Group III-VI compound having an amorphous or microcrystalline structure; and a buffer layer 5 which is positioned on the intermediate layer 4 and contains a Group VI compound having a crystal structure.

Description

  The present invention relates to a photoelectric conversion device including 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 light absorption layer is formed of a chalcopyrite structure I-III-VI group compound semiconductor such as CIGS (for example, Patent Document 1). The chalcopyrite-structured I-III-VI compound semiconductor has a high light absorption coefficient and is suitable for reducing the thickness, area, and manufacturing cost of the photoelectric conversion device. The chalcopyrite-structured I-III-VI Research and development of next-generation solar cells using Group III compound semiconductors is underway.

  In such a photoelectric conversion device, a lower electrode such as Mo, a light absorption layer, a buffer layer such as a sulfur-containing zinc mixed crystal compound, and an upper electrode such as ZnO are arranged in this order on a substrate such as glass. It is configured by stacking. This buffer layer is formed by crystal growth on the light absorption layer by a CBD (Chemical Bath Deposition) method.

JP-A-8-330614

  The photoelectric conversion device is required to further improve the conversion efficiency. This conversion efficiency indicates the rate at which light energy is converted into electrical energy in the photoelectric conversion device. For example, the value of electrical energy output from the photoelectric conversion device is the value of light energy incident on the photoelectric conversion device. Divided by 100 and multiplied by 100.

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

  A photoelectric conversion device according to an embodiment of the present invention includes a light absorption layer containing a chalcopyrite structure I-III-VI group compound, and an amorphous or microcrystalline structure III-VI group compound located on the light absorption layer And a buffer layer containing a group VI compound having a crystal structure located on the intermediate layer.

  According to the present invention, the presence of the intermediate layer improves the bonding between the light absorption layer and the buffer layer, and the conversion efficiency in the photoelectric conversion device is improved.

It is a perspective view of the photoelectric conversion apparatus which concerns on one Embodiment. 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 of the modification of a photoelectric conversion apparatus.

  Hereinafter, 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 top view illustrating a configuration of the photoelectric conversion device 21. FIG. 2 is a cross-sectional view of the photoelectric conversion device 21 of FIG.

  The photoelectric conversion device 21 has a configuration in which a plurality of photoelectric conversion cells 20 are arranged in parallel on the substrate 1. In FIG. 1, only two photoelectric conversion cells 20 are shown for convenience of illustration. However, in an actual photoelectric conversion device 21, a large number of photoelectric conversion cells 20 are two-dimensionally (two Are dimensionally arranged.

  Each photoelectric conversion cell 20 mainly includes a lower electrode layer 2, a light absorption layer 3, an intermediate layer 4, a buffer layer 5, an upper electrode layer 6, and a grid electrode 7. In the photoelectric conversion device 21, the main surface on the side where the upper electrode layer 6 and the grid electrode 7 are provided is a light receiving surface. In addition, the photoelectric conversion device 21 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 20 and is made of, for example, a material such as glass, ceramics, resin, or metal. Here, the board | substrate 1 shall be comprised with the blue plate glass (soda lime glass) which has a thickness of about 1-3 mm.

  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). Including metals such as Or the laminated structure of these metals may be sufficient. 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 having a first conductivity type (here, p-type conductivity type) provided on one main surface of the lower electrode layer 2 and having a thickness of about 1 to 3 μm. Have. The light absorption layer 3 is a semiconductor layer mainly containing a chalcopyrite structure I-III-VI group compound. Here, it is assumed that the light absorption layer 3 is mainly composed of a chalcopyrite structure I-III-VI group compound having p-type conductivity.

Here, the I-III-VI group compound includes a group IB element (also referred to as a group 11 element), a group III-B element (also referred to as a group 13 element), and a group VI-B element (also referred to as a group 16 element). And the compound. Examples of the I-III-VI group compound include CuInSe ₂ (also referred to as copper indium diselenide, CIS), Cu (In, Ga) Se ₂ (also referred to as copper indium diselenide / gallium, CIGS), Cu (In, Ga) (Se, S) ₂ (also referred to as diselene, copper indium gallium sulfide, gallium, CIGSS), and the like can be given. The light absorption layer 3 may be formed of a thin film of a multi-component compound semiconductor such as copper indium selenide and indium gallium selenide having a thin film of selenite, copper indium sulfide and gallium as a surface layer. Here, it is assumed that the light absorption layer 3 is made of CIGS.

Such a light absorption layer 3 is produced as follows, for example. First, a IB group element and a III-B group element are supplied onto the lower electrode layer 2 by a method such as vapor deposition or sputtering to form a precursor layer. Alternatively, a precursor layer is formed by applying a raw material solution containing a group I-B element and a group III-B element on the lower electrode layer 2. These precursor layers may contain a VI-B group element. These precursor layers may be a plurality of laminated bodies having different composition ratios. And this I-III-VI group compound is formed by heating this precursor layer in the atmosphere containing a chalcogen element. In addition, a chalcogen element means S, Se, and Te among VI-B group elements.

  From the viewpoint that the intermediate layer 4 described later is formed satisfactorily, the light absorption layer 3 is formed of a precursor layer using a raw material solution containing a complex compound of an organic ligand and a metal element. The body layer may be formed by heating. Even when the precursor layer containing such an organic ligand is heated, the organic component tends to remain in the light absorption layer 3 in some state. When the intermediate layer 4 is formed on the light absorption layer 3 having such organic component residue, the residue suppresses the crystallization of the intermediate layer 4, so that the intermediate layer 4 is in an amorphous or microcrystalline structure state. It becomes easy to become.

  From the viewpoint of improving the formation of the light absorption layer 3 and the formation of the intermediate layer 4, the organic ligand may be a chalcogen element-containing organic compound. The chalcogen element-containing organic compound is an organic compound having a bond between a chalcogen element and carbon. Examples include thiol, sulfide, disulfide, thiophene, sulfoxide, sulfone, thioketone, sulfonic acid, sulfonic acid ester, sulfonic acid amide, selenol, selenide, diselenide, selenoxide, selenone, tellurol, telluride, ditelluride and the like. In particular, thiol, sulfide, disulfide, selenol, selenide, diselenide, tellurol, telluride, ditelluride may be used from the viewpoint of high coordination power and easy formation of a stable complex with a metal element.

  Examples of such a complex compound of an organic ligand and a metal element include a group I-B element and a group III-B element in one molecule as described in US Pat. No. 6,992,202. And a complex compound containing a chalcogen element-containing organic compound. Or the mixture of the complex compound of a IB group element and a chalcogen element containing organic compound and the complex compound of a III-B group element and a chalcogen element containing organic compound may be sufficient.

The intermediate layer 4 is a semiconductor layer containing a group III-VI compound having an amorphous or microcrystalline structure. Note that the microcrystalline structure is mainly composed of nano-sized crystal particles having an average particle diameter of 10 nm or less, and is a state close to an amorphous state that almost shows a crystal peak by X-ray diffraction. Examples of the III-VI group compound include Ga ₂ S ₃ and In ₂ S ₃ .

  By having the intermediate layer 4 having an amorphous or microcrystalline structure, one main surface of the light absorption layer 3 can be smoothed. As a result, the buffer layer 5 having a crystal structure can be satisfactorily bonded to the light absorption layer 3 through the intermediate layer 4, and the conversion efficiency of the photoelectric conversion layer 21 is improved. Note that if the intermediate layer 4 is in a more amorphous state, the bondability between the light absorption layer 3 and the first semiconductor layer 5 is further improved. From such a viewpoint, the intermediate layer 4 may be amorphous or have a microcrystalline structure with an average particle diameter of 5 nm or less.

  From the viewpoint of enhancing the adhesion with the light absorption layer 3, the group III-B element contained in the intermediate layer 4 may be the same as the group III-B element contained in the light absorption layer 3. In particular, from the viewpoint of easy production of the intermediate layer 4 having an amorphous or microcrystalline structure, the light absorption layer 3 contains Ga as a group III element and Se as a group VI element, and the intermediate layer 4 contains Ga as a group III element. It may contain S as a group VI element.

  The thickness of the intermediate layer 4 is about 1/100 to 1/5 of the thickness of the first semiconductor layer 5 from the viewpoint of improving charge transfer. Specifically, the intermediate layer 4 has a thickness of about 1 nm to 200 nm, for example.

  When the cross section of the intermediate layer 4 is analyzed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), the crystallinity of the intermediate layer 4 is determined when grains cannot be confirmed or the average grain size is 10 nm or less. Or the presence of an intermediate layer mainly composed of Group III and Group VI, but when no crystal peak is observed by X-ray diffraction, the amorphous or microcrystalline structure is confirmed.

  Such an intermediate layer 4 is produced by the following method, for example. First, the light absorption layer 3 is formed on the lower electrode layer 2 by a known method. Next, a film containing a III-B group element is formed on the light absorption layer 3, and this film is heated in an atmosphere containing a VI-B group element to become a III-VI group compound. This heat treatment is completed when the III-VI group compound is in an amorphous or microcrystalline structure.

  Alternatively, a film containing a III-B group element and a VI-B group element may be formed on the light absorption layer 3, and the film may be heated to form a III-VI group compound. Also in this case, the heat treatment is completed in a state where the III-VI group compound is in an amorphous or microcrystalline structure.

As another method for producing the intermediate layer 4, the following method may be employed. First, the light absorption layer 3 is formed on the lower electrode layer 2 by a known method. Next, the light absorption layer 3 is heat-treated in an atmosphere containing sulfur vapor (hereinafter also referred to as S vapor). The atmosphere containing S vapor is one in which solid sulfur is heated and evaporated in an inert gas such as nitrogen or a reducing gas such as hydrogen, and S vapor is mixed in the atmosphere. Such S vapor is formed tends liquid layer with deposited on the surface of the light absorbing layer 3 in a state of the cluster, such as S _8. This liquid layer of sulfur reacts with the III-B group element on the surface of the light absorption layer 3, and the intermediate layer 4 containing the III-VI group compound having an amorphous or microcrystalline structure is satisfactorily formed.

  In the case where the intermediate layer 4 is formed by heating in an atmosphere containing S vapor as described above, from the viewpoint of better forming the intermediate layer 4, the light absorption layer 3 is at least in the surface portion. The number of moles of the group element may be slightly larger than the number of moles of the group III-B element. In this case, the number of moles of the group IB element is, for example, about 0.80 to 0.99 times the number of moles of the group III-B element. Thereby, the III-B group element which exists excessively and sulfur react more favorably.

  Further, when the intermediate layer 4 is formed by heating in an atmosphere containing S vapor as described above, the group III-B element contained in the light absorption layer 3 may contain gallium. Gallium tends to proceed more favorably with sulfur, and the intermediate layer 4 mainly containing gallium sulfide is formed better.

  Further, when the intermediate layer 4 is formed by heating in an atmosphere containing S vapor as described above, selenium is included as a VI-B group element of the I-III-VI group compound contained in the light absorption layer 3. May be. When selenium is contained in the I-III-VI group compound, selenium is replaced with sulfur by heating in an atmosphere containing S vapor, and a compound of a III-B group element and sulfur is easily formed.

The buffer layer 5 is a semiconductor layer provided on one main surface of the light absorption layer 3 via the intermediate layer 4. This semiconductor layer has a conductivity type (here, n-type conductivity type) different from the conductivity type of the light absorption layer 3. Moreover, the buffer layer 5 is provided in a mode of heterojunction with the light absorption layer 3 mainly composed of the I-III-VI group compound semiconductor. Note that semiconductors having different conductivity types are semiconductors having different conductive carriers. Moreover, when the conductivity type of the light absorption layer 3 is p-type as described above, the conductivity type of the buffer layer 5 may be i-type instead of n-type. Further, there may be an embodiment in which the light absorption layer 3 has an n-type or i-type conductivity and the buffer layer 5 has a p-type conductivity.

The buffer layer 5 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, etc. From the viewpoint of reducing the leakage current, the buffer layer 5 may have a resistivity of 1 Ω · cm or more. The buffer layer 5 is crystal-grown by, for example, a chemical bath deposition (CBD) method.

  From the viewpoint of improving electrical connection with the light absorption layer 3, S may be included as a group VI element of the buffer layer 5. In this case, if the group VI element of the intermediate layer 4 also contains S, the buffer layer 5 can be formed better on the intermediate layer 4.

  The thickness of the buffer layer 5 is set to 10 to 200 nm. From the viewpoint of suppressing damage when the upper electrode layer 6 is formed on the buffer layer 5 by sputtering or the like, the thickness may be 100 to 200 nm.

  The upper electrode layer 6 is a transparent conductive film having an n-type conductivity provided on the buffer layer 5, and is an electrode for extracting charges generated in the light absorption layer 3. The upper electrode layer 6 is made of a material having a lower resistivity than the buffer layer 5. The upper electrode layer 6 includes what is called a window layer. When a transparent conductive film is further provided in addition to the window layer, these may be regarded as an integrated upper electrode layer 6.

The upper electrode layer 6 may be made of a transparent, low-resistance material having a wide forbidden band, such as a metal oxide semiconductor such as ZnO, In ₂ O ₃ , and SnO ₂ . These metal oxide semiconductors may contain any element such as Al, B, Ga, In, and F. Specific examples of the metal oxide semiconductor containing such an element include, for example, AZO (Aluminum Zinc Oxide), GZO (Gallium Zinc Oxide), IZO (Indium Zinc Oxide), and ITO (Indium).
Tin Oxide) and FTO (fluorine tin oxide).

  The upper electrode layer 6 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 obtaining good charge from the light absorption layer 3, the upper electrode layer 6 may have a resistivity of less than 1 Ω · cm and a sheet resistance of 50Ω / □ or less.

  The buffer layer 5 and the upper electrode layer 6 may be a material having a property (also referred to as light transmission property) that allows light to easily pass through the wavelength region of light absorbed by the light absorption layer 3. Thereby, the fall of the light absorption efficiency in the light absorption layer 3 produced by providing the buffer layer 5 and the upper electrode layer 6 is suppressed.

  Further, from the viewpoint of enhancing the light transmittance and at the same time enhancing the effect of preventing the loss of light reflection, and further transmitting the current generated by the photoelectric conversion, the upper electrode layer 6 has a thickness of 0. You may have thickness of 05-0.5 micrometer. Furthermore, in terms of preventing loss of light reflection at the interface between the upper electrode layer 6 and the buffer layer 5, the absolute refractive index may be substantially the same between the upper electrode layer 6 and the buffer layer 5. .

  The grid electrode 7 is an electrode having conductivity, and is made of a metal such as silver (Ag), for example. It plays a role of collecting charges generated in the light absorption layer 3 and taken out in the upper electrode layer 6. Although the grid electrode 7 may not be provided, if the grid electrode 7 is provided, the upper electrode layer 6 can be thinned.

  The charges collected by the grid electrode 7 and the upper electrode layer 6 are transmitted to the adjacent photoelectric conversion cell 20 through the connection portion 8 provided in the second groove portion P2. As shown in FIGS. 1 and 2, the connecting portion 8 may be provided with the grid electrode 7 extended. Alternatively, the connection portion 8 may be provided by extending the upper electrode layer 6 or may be provided by filling the second groove portion P2 with another conductive member. Thereby, in the photoelectric conversion device 21, one lower electrode layer 2 of the adjacent photoelectric conversion cell 20, the other upper electrode layer 6 and the grid electrode 7 are connected to each other by the connection portion 8 provided in the second groove portion P2. The connecting conductor is electrically connected in series.

  The grid electrode 7 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 absorption layer 3 is minimized. Also good.

<(2) Manufacturing method of photoelectric conversion device>
3 to 7 are cross-sectional views each schematically showing a state during the manufacture of the photoelectric conversion device 21. 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 the substantially entire surface of the cleaned substrate 1 using a sputtering method or the like. Then, the first groove portion P1 is formed from the upper surface of the lower electrode layer 2 to the upper surface of the substrate 1 immediately below it. The first groove portion P1 is preferably formed by, for example, scribe processing in which groove processing is performed by irradiating a formation target position while scanning with a laser beam by a YAG laser or the like. FIG. 3 is a diagram illustrating a state after the first groove portion P1 is formed.

  After the first groove portion P1 is formed, the light absorption layer 3 and the intermediate layer 4 are formed on the lower electrode layer 2 by the method described above. FIG. 4 is a diagram illustrating a state after the light absorption layer 3 and the intermediate layer 4 are formed.

  After the light absorption layer 3 and the intermediate layer 4 are formed, the buffer layer 5 and the upper electrode layer 6 are formed on the intermediate layer 4. FIG. 5 is a diagram showing a state after the buffer layer 5 and the upper electrode layer 6 are formed.

  The buffer layer 5 is formed by a solution growth method (also referred to as CBD method). For example, the buffer layer 5 containing CdS is formed on the intermediate layer 4 by immersing the substrate 1 in which cadmium acetate and thiourea are dissolved in aqueous ammonia and the intermediate layer 4 is formed. Is done. The upper electrode layer 6 is formed by sputtering, vapor deposition, CVD, or the like.

After the upper electrode layer 6 is formed, a second groove portion P2 is formed from the upper surface of the upper electrode layer 6 to the upper surface of the lower electrode layer 2 immediately below it. The second groove portion P2 is 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 pitch. Further, 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 one to several scribes. 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 shifted from the first groove portion P1.

  After the second groove portion P2 is formed, the grid electrode 7 is formed on the upper electrode layer 6. For the grid electrode 7, 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, and this is solidified. Formed with. When the conductive paste is printed on the upper electrode layer 6, the second paste P <b> 2 may be filled with the conductive paste. Thereby, the connection part 8 which electrically connects the grid electrode 7 and the lower electrode layer 2 is formed in the same process as the formation of the grid electrode 7, and the process is simplified. FIG. 7 is a diagram illustrating a state after the grid electrode 7 and the connection portion 8 are formed.

  After the grid electrode 7 and the connection portion 8 are formed, the third groove portion P3 is formed from the upper surface of the grid electrode 7 and the upper surface of the upper electrode layer 6 to the upper surface of the lower electrode layer 2 immediately below it. The width of the third groove portion P3 is preferably about 40 to 1000 μm, for example. Moreover, the 3rd groove part P3 may be formed by mechanical scribing similarly to the 2nd groove part P2. In this way, the photoelectric conversion device 21 shown in FIGS. 1 and 2 is manufactured by forming the third groove portion P3.

<(3) Modification>
It should be noted that the present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the gist of the present invention.

  FIG. 8 is a cross-sectional view of a modification of the photoelectric conversion device. 8, parts having the same configuration and function as those in FIG. 1 are denoted by the same reference numerals. The photoelectric conversion device 31 as a modified example is different from the photoelectric conversion device 21 in FIG. 1 in that the intermediate layer 4 ′ has a non-formed part. The light absorption layer 3 and the buffer layer 5 are connected to each other in the non-formed portion of the intermediate layer 4 ′. Accordingly, the bonding property between the light absorption layer 3 and the buffer layer 5 is enhanced by the intermediate layer 4 ′, charge transfer is performed well in the non-formed portion, and the photoelectric conversion efficiency is further increased.

  Needless to say, all or a part of each of the above-described embodiment and modification examples can be appropriately combined within a consistent range.

1: Substrate 2: Lower electrode layer 3: Light absorption layer 4: Intermediate layer 5: Buffer layer 6: Upper electrode layer 7: Grid electrode 20, 30: Photoelectric conversion cell 21, 31: Photoelectric conversion device

Claims (4)

A light absorbing layer containing a chalcopyrite structure I-III-VI group compound;
An intermediate layer containing an III-VI group compound having an amorphous or microcrystalline structure located on the light absorption layer;
And a buffer layer containing a group VI compound having a crystal structure located on the intermediate layer.   The photoelectric conversion device according to claim 1, wherein the intermediate layer has a non-forming portion, and the light absorption layer and the buffer layer are connected to each other at the non-forming portion.   The photoelectric absorption layer according to claim 1 or 2, wherein the light absorption layer contains gallium as a group III element and selenium as a group VI element, and the intermediate layer contains gallium as a group III element and sulfur as a group VI element. Conversion device.   The photoelectric conversion device according to claim 1, wherein the buffer layer contains sulfur as a group VI element.

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