JP5832229B2 - Photoelectric conversion device - Google Patents

Description

  The present invention relates to a photoelectric conversion device using a group I-III-VI compound semiconductor.

As a photoelectric conversion device such as a solar cell, there is one using a chalcopyrite-based I-III-VI group compound semiconductor as a light absorption layer. In this photoelectric conversion device, for example, an electrode layer made of Mo is formed on a substrate made of soda lime glass, and a light absorption layer is formed on the electrode layer. Further, a transparent transparent conductive film made of ZnO, ITO or the like is formed on the light absorption layer through a buffer layer containing ZnS, CdS, In ₂ S ₃ or the like.

Japanese Patent Laid-Open No. 08-330614

  The photoelectric conversion device is desired to further improve the photoelectric conversion efficiency. Therefore, an object of the present invention is to provide a photoelectric conversion device with high photoelectric conversion efficiency.

  A photoelectric conversion device according to an embodiment of the present invention includes an electrode layer, an I-III-VI group compound semiconductor layer containing a gallium element located on the electrode layer, the electrode layer, and the I-III-VI group And an intermediate layer containing a larger amount of a gallium element and an oxygen element than the I-III-VI group compound semiconductor layer, which are arranged independently at the interface of the compound semiconductor layer.

  ADVANTAGE OF THE INVENTION According to this invention, a photoelectric conversion apparatus with high photoelectric conversion efficiency can be provided.

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.

<(1) Configuration of photoelectric conversion device>
FIG. 1 is a sectional view showing a photoelectric conversion device according to an embodiment of the present invention, and FIG. 2 is a sectional view thereof. 1 and 2 are assigned the same reference numerals. The photoelectric conversion device 11 includes a substrate 1, a first electrode layer 2, an intermediate layer 3, an I-III-VI group compound semiconductor layer (hereinafter also referred to as a first semiconductor layer) 4, and a second semiconductor. A layer 5 and a second electrode layer 6 are provided.

  The first semiconductor layer 4 and the second semiconductor layer 5 have different conductivity types, and the first semiconductor layer 4 and the second semiconductor layer 5 have good charge separation of positive and negative carriers generated by light irradiation. It can be carried out. For example, if the first semiconductor layer 4 is p-type, the second semiconductor layer 5 is n-type. Alternatively, the second semiconductor layer 5 may be a plurality of layers including a buffer layer and a semiconductor layer having a conductivity type different from that of the first semiconductor layer 4. In the present embodiment, an example is shown in which the first semiconductor layer 4 is a one-conductivity type light absorption layer, and the second semiconductor layer 5 serves as both a buffer layer and the other conductivity-type semiconductor layer.

  Moreover, although the photoelectric conversion apparatus 11 in this embodiment has shown what injects light from the 2nd electrode layer 6 side, it is not limited to this, Light is incident from the board | substrate 1 side, Also good.

  In FIG. 1, the photoelectric conversion device 11 is formed by arranging a plurality of photoelectric conversion cells 10. The photoelectric conversion cell 10 includes a third electrode layer 9 provided on the substrate 1 side of the first semiconductor layer 4 so as to be separated from the first electrode layer 2. The second electrode layer 6 and the third electrode layer 9 are electrically connected by the connection conductor 7 provided in the first semiconductor layer 4. In FIG. 1, the third electrode layer 9 is obtained by extending the first electrode layer 2 of the adjacent photoelectric conversion cell 10. With this configuration, adjacent photoelectric conversion cells 10 are connected in series. In one photoelectric conversion cell 10, the connection conductor 7 is provided so as to penetrate the first semiconductor layer 4 and the second semiconductor layer 5, and the first electrode layer 2 and the second electrode layer are provided. Photoelectric conversion is performed between the first semiconductor layer 4 and the second semiconductor layer 5 sandwiched between the first semiconductor layer 4 and the second semiconductor layer 5.

  The substrate 1 is for supporting the first semiconductor layer 4 and the second semiconductor layer 5. Examples of the material used for the substrate 1 include glass, ceramics, resin, and metal.

  The first electrode layer 2 and the third electrode layer 9 are made of a conductor selected from Mo, Al, Ti, Au, and the like, and are formed on the substrate 1 by a method selected from sputtering, vapor deposition, and the like. .

A plurality of intermediate layers 3 are arranged independently at the interface between the first electrode layer 2 and the first semiconductor layer 4. In other words, the intermediate layer 3 is scattered at the interface between the first electrode layer 2 and the first semiconductor layer 4. Further, the intermediate layer 3 contains more gallium element and oxygen element than the first semiconductor layer 4. That is, the average content of gallium elements in the intermediate layer 3 is higher than the average content of gallium elements in the first semiconductor layer 4 and the average content of oxygen elements in the first semiconductor layer 4 (first The average content of oxygen element in the intermediate layer 3 is greater than that in which the semiconductor layer 4 may not contain oxygen element). It is considered that such an intermediate layer 3 is likely to exist as gallium oxide such as Ga ₂ O ₃ . By providing such an intermediate layer 3, the adhesiveness between the first semiconductor layer 4 and the first electrode layer 2 can be improved and the recombination of carriers can be reduced. As a result, the photoelectric conversion efficiency of the photoelectric conversion device 11 is improved.

  The intermediate layer 3 may be, for example, in the form of particles of about several nm to several tens of nm scattered at the interface between the first electrode layer 2 and the first semiconductor layer 4. With such a configuration, charge transfer between the first semiconductor layer 4 and the first electrode layer 2 is favorably performed, and the photoelectric conversion efficiency of the photoelectric conversion device 11 is further improved.

  From the viewpoint of further increasing the photoelectric conversion efficiency in the first semiconductor layer 4, the first semiconductor layer 4 may further contain an indium element. Further, in this case, in the first semiconductor layer 4, the Ga molar ratio (Ga / (In + Ga)) to the total number of moles of group III-B elements (In + Ga) (Ga / (In + Ga)) increases as the distance from the first electrode layer 2 increases. Thus, the Ga concentration may be inclined. This tilts the conduction band and further improves charge transfer.

  The thickness of the intermediate layer 3 may be 0.001 μm or more from the viewpoint of enhancing durability against environmental changes such as temperature difference. Further, the thickness of the intermediate layer 3 may be 0.2 μm or less from the viewpoint of improving charge transfer. Moreover, if the thickness of the intermediate | middle layer 3 is 0.005 micrometer or more and 0.03 micrometer or less, photoelectric conversion efficiency will be maintained highly over a long period of time.

  The intermediate layer 3 may have an amorphous or microcrystalline structure. In this case, the adhesion between the first semiconductor layer 4 and the first electrode layer 2 is further improved. Note that the microcrystalline structure means a structure mainly composed of nano-sized crystal particles having an average particle size of 10 nm or less.

The first semiconductor layer 4 is a semiconductor layer mainly containing an I-III-VI group compound having a chalcopyrite structure. The I-III-VI group compound semiconductor is a compound semiconductor (group 16 element) of 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. It is also called). The first semiconductor layer 4 contains at least Ga as a III-B group element. Examples of such an I-III-VI group compound semiconductor include Cu (In, Ga) Se ₂ (also referred to as CIGS), Cu (In, Ga) (Se, S) ₂ (also referred to as CIGSS), and CuGaSe. ₂ (also referred to as CGS). Cu (In, Ga) Se ₂ refers to a compound mainly composed of Cu, In, Ga, and Se. Cu (In, Ga) (Se, S) ₂ refers to a compound containing Cu, In, Ga, Se, and S as main components.

The second semiconductor layer 5 is formed on the first semiconductor layer 4. In the present embodiment, an example is shown in which the first semiconductor layer 4 is a one-conductivity type light absorption layer, and the second semiconductor layer 5 serves as both a buffer layer and the other conductivity-type semiconductor layer. From the viewpoint of reducing leakage current, the second semiconductor layer 5 may have a resistivity of 1 Ω · cm or more. Examples of the second semiconductor layer 5 include CdS, ZnS, ZnO, In ₂ Se ₃ , In (OH, S), (Zn, In) (Se, OH), and (Zn, Mg) O. The second semiconductor layer 5 is formed by, for example, a chemical bath deposition (CBD) method or the like. Note that In (OH, S) refers to a compound containing In, OH, and S as main components. (Zn, In) (Se, OH) refers to a compound containing Zn, In, Se, and OH as main components. (Zn, Mg) O refers to a compound containing Zn, Mg, and O as main components. In order to increase the absorption efficiency of the first semiconductor layer 4, the second semiconductor layer 5 may have a high light transmittance with respect to the wavelength region of light absorbed by the first semiconductor layer 4.

  The second semiconductor layer 5 has a thickness of 10 to 200 nm. From the viewpoint of suppressing damage when the second electrode layer 6 is formed on the second semiconductor layer 5 by sputtering or the like, the thickness of the second semiconductor layer 5 can be 100 to 200 nm.

  The second electrode layer 6 is a transparent conductive film having a thickness of 0.05 to 3.0 μm, such as ITO or ZnO. The second electrode layer 6 is formed by sputtering, vapor deposition, chemical vapor deposition (CVD), or the like. The second electrode layer 6 is a layer having a resistivity lower than that of the second semiconductor layer 5, and is for taking out electric charges generated in the first semiconductor layer 4. From the viewpoint of taking out charges well, the resistivity of the second electrode layer 6 may be less than 1 Ω · cm and the sheet resistance may be 50 Ω / □ or less.

  As the second electrode layer 6, a material having high light transmittance with respect to the absorbed light of the first semiconductor layer 4 may be used in order to increase the absorption efficiency of the first semiconductor layer 4. The second electrode layer 6 has a thickness of 0.05 to 0.5 μm from the viewpoint of enhancing the light transmittance and at the same time enhancing the light reflection loss reducing effect and the light scattering effect and further transmitting the current generated by the photoelectric conversion. It may be a thickness. Further, from the viewpoint of reducing light reflection loss at the interface between the second electrode layer 6 and the second semiconductor layer 5, the refractive indexes of the second electrode layer 6 and the second semiconductor layer 5 are substantially equal. Also good.

  A collecting electrode 8 may be provided on the second electrode layer 6. By providing the current collecting electrode 8, the thickness of the second electrode layer 6 can be reduced to increase the light transmittance, and the current generated in the first semiconductor layer 4 can be efficiently extracted. As a result, the photoelectric conversion efficiency of the photoelectric conversion device 11 is increased.

  The width of the current collecting electrode 8 can be set to 50 to 400 μm from the viewpoint of reducing light shielding to the first semiconductor layer 4 and having good conductivity. The current collecting electrode 8 may have a plurality of branched portions.

  The current collecting electrode 8 is formed, for example, by printing a conductive paste in which a metal powder such as Ag is dispersed in a resin binder or the like in a pattern and curing it.

  A plurality of photoelectric conversion cells 10 are arranged and electrically connected to form a photoelectric conversion device 11. In order to easily connect adjacent photoelectric conversion cells 10 in series, as shown in FIG. 1, the photoelectric conversion cell 10 is separated from the first electrode layer 2 on the substrate 1 side of the first semiconductor layer 4. A third electrode layer 9 is provided. The second electrode layer 6 and the third electrode layer 9 are electrically connected by the connection conductor 7 provided in the first semiconductor layer 4. In FIG. 1 and FIG. 2, the connection conductor 7 is formed by extending a part of the current collecting electrode 8 so as to reach the third electrode layer 9.

<(2) Manufacturing method of photoelectric conversion device>
The first semiconductor layer 4 is produced as follows. First, a substrate 1 having a first electrode layer 2 having a desired pattern divided by the grooves P1 provided on the surface is prepared. Next, a film is formed on the first electrode layer 2 using a raw material solution containing an IB group element and an III-B group element. In the raw material solution, a group IB element and a group III-B element are dissolved in various compounds in a solvent such as an organic solvent. The mixing ratio of the group I-B element and the group III-B element in the raw material solution is adjusted so that the group III-B element is in excess of the theoretical ratio of the group I-III-VI compound. As a method for forming a film using a raw material solution, a method using a spin coater, screen printing, dipping, spraying, or a die coater is used. The raw material solution may contain a VI-B group element.

  Next, the film is dried at a temperature of 50 to 350 ° C. in an atmosphere containing water or oxygen. In this drying, the organic components may be evaporated or pyrolyzed. At the time of drying, at least a part of the IB group element and the III-B group element in the film is oxidized to form an oxide. In addition, when the solvent containing oxygen, such as alcohol, is used as the solvent of the raw material solution used when forming the film, the formation of the oxide is further promoted.

  Next, the dried film is heated at a temperature of 400 to 600 ° C. in an atmosphere containing a chalcogen element (the chalcogen element refers to S, Se, and Te among VI-B group elements). During this heating, oxygen in the film is replaced by the chalcogen element, and this chalcogen element reacts with the IB group element and the III-B group element to form an I-III-VI group compound and crystallize. As the I-III-VI group compound is generated, the chalcogen element in the atmosphere is less likely to reach the vicinity of the interface with the first electrode layer 2 of the coating. As a result, in the portion of the film near the interface with the first electrode layer 2, the excessively contained III-B group element oxide remains to form the intermediate layer 3, and in other portions, the first semiconductor layer. 4 is considered. By such a method, the intermediate layer 3 and the first semiconductor layer 4 are formed in the same process, and the process is simplified. When the above film is heated in an atmosphere containing a chalcogen element, crystallization on the upper surface side of the film is promoted if heated by IR irradiation from above the film with an IR lamp or the like. Thus, the intermediate layer 3 is more easily formed.

  Regarding the constituent elements of the generated intermediate layer 3 and the first semiconductor layer 4, each cross section of the intermediate layer 3 and the first semiconductor layer 4 has an energy dispersive x-ray spectroscopy (EDS). ) To be identified. Alternatively, X-ray photoelectron spectroscopy (XPS), Auger Electron Spectroscopy (AES), or secondary ion mass while scraping the first semiconductor layer 4 and the intermediate layer 3 in the depth direction by sputtering. Analysis may be performed by an analysis method (SIMS: Secondary Ion Mass Spectroscopy) or the like.

  The production of the intermediate layer 3 and the first semiconductor layer 4 is not limited to the above process, and may be formed by other methods. For example, the intermediate layer 3 may be first formed on the first electrode layer 2 by sputtering or the like, and the first semiconductor layer 4 may be formed on the intermediate layer 2.

  After the intermediate layer 3 and the first semiconductor layer 4 are formed as described above, the second semiconductor layer 5 is formed on the first semiconductor layer 4 by the CBD method or the like, and the sputtering method is formed thereon. Thus, the second electrode layer 6 is formed.

  Next, a part of the laminated body of the intermediate layer 3, the first semiconductor layer 4, the second semiconductor layer 5, and the second electrode layer 6 is removed by mechanical scribing or the like to form the connection conductor 7 A groove P2 is formed. Then, a metal paste is printed on the second electrode layer 6 by a screen printing method or the like, and the metal paste is also filled in the groove P2, whereby the collecting electrode 8 and the connection conductor 7 are formed.

  Finally, the laminated body from the intermediate layer 3 to the collector electrode 8 at a position slightly deviated from the connection conductor 7 is removed by mechanical scribing or the like, so that a groove P3 for separation into individual photoelectric conversion cells 10 is formed. It is formed. Thus, the photoelectric conversion device 11 in which the adjacent photoelectric conversion cells 10 are connected in series is completed.

  Note that the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the present invention.

<Preparation of raw material solution>
First, single source precursors containing a group I-B element, a group III-B element, and a group VI-B element in one molecule were prepared as shown in a1 to a3 below.

[A1] 10 mmol (mmol) of Cu (CH ₃ CN) ₄ .PF ₆ and 100 mmol of P (C ₆ H ₅ ) ₃ were dissolved in 100 ml of acetonitrile, and then ₅ at room temperature (25 ° C.). A first complex solution was prepared by stirring over time.

[A2] 40 mmol of sodium methoxide (CH ₃ ONa) and 40 mmol of phenylselenol (C ₆ H ₅ SeH) which is a chalcogen element-containing organic compound were dissolved in 300 ml of methanol, and further 6 mmol of InCl _3. And 4 mmol of GaCl ₃ were dissolved, and then a second complex solution was prepared by stirring at room temperature for 5 hours.

  [A3] The second complex solution prepared in step [a2] was added dropwise to the first complex solution prepared in step [a1], and a precipitate was formed. The precipitate is extracted, washed with methanol, and dried at room temperature to obtain a precipitate containing a mixture of single source precursors as shown in general formula (1) and general formula (2). It was. In this mixture of single source precursors, one complex molecule includes Cu, Ga, and Se, or includes Cu, In, and Se.

  Next, a compound containing a gallium element was prepared as in the following b1 to b3.

  [B1] 10 mmol of aniline and 10 mmol of phenylselenol were mixed to prepare a mixed solution M.

  [B2] 2 mmol of metal Ga was dissolved in the mixed solution M.

  [B3] By adding hexane to the mixed solution M in which this gallium was dissolved, a precipitate containing a complex compound of Ga and phenyl selenol was deposited, and this precipitate was taken out.

  Next, the precipitate containing the single source precursor obtained in [a3] and the precipitate containing the Ga complex compound obtained in [b3] are dissolved in pyridine to prepare a raw material solution. It was.

<Production of first semiconductor layer>
Next, a plurality of substrates in which a first electrode layer containing Mo or the like was formed on the surface of a substrate containing glass was prepared. Then, in a nitrogen gas atmosphere, the raw material solution was applied on each first electrode layer by a blade method to form a film.

  Next, these coatings are in an atmosphere of nitrogen gas having moisture at respective concentrations of 50 ppmv (sample No. 1), 100 ppmv (sample No. 2), 150 ppmv (sample No. 3), and 0 ppmv (sample No. 4). The IR light was irradiated from the surface. Thereby, the film was heated at 300 ° C. for 10 minutes, and the organic components in the film were removed by thermal decomposition.

  Next, each film from which these organic components have been removed is mainly heated by heating at 300 ° C. for 15 minutes and further at 550 ° C. for 1 hour in a mixed gas atmosphere of Se vapor (5 ppmv) and hydrogen gas. A first semiconductor layer containing CIGS was formed.

<Production of photoelectric conversion device>
A second semiconductor layer and a second electrode layer were sequentially formed on each first semiconductor layer manufactured as described above to manufacture a photoelectric conversion device.

  Specifically, the substrate on which the first semiconductor layer is formed is immersed in a solution in which cadmium acetate and thiourea are dissolved in ammonia water, whereby a thickness of 50 nm is formed on the first semiconductor layer. A second semiconductor layer containing CdS was formed. Furthermore, a second electrode layer containing zinc oxide doped with Al was formed on the second semiconductor layer by a sputtering method.

  Sample No. manufactured as described above was obtained. 1 to 4 were subjected to SEM observation of the cross section. As for samples 1 to 3, the first semiconductor layer having a diameter of about 5 to 40 nm was formed at the interface between the first semiconductor layer and the first electrode layer. It was found that phase regions different from those were scattered along the first electrode layer, and an intermediate layer was formed. In Sample 4, such an intermediate layer was not observed.

  These sample Nos. Composition analysis was performed on the first to fourth first semiconductor layers and intermediate layers by transmission electron microscope analysis (TEM). In addition, the average gallium content rate and the average oxygen content rate of the first semiconductor layer are average values of measurement results at arbitrary 10 points of the first semiconductor layer. Further, the average gallium content and the average oxygen content of the intermediate layer were measured by measuring the content at each central part of any 10 phase regions interspersed, and the average value of these 10 measurement results was calculated. Is. Sample No. The results of the composition analysis of 1-4 are shown in Table 1.

  From Table 1, Sample No. It was found that the intermediate layers 1 to 3 had higher gallium content and oxygen content than the average gallium content and average oxygen content of the first semiconductor layer.

<Measurement of photoelectric conversion efficiency in photoelectric conversion device>
The photoelectric conversion efficiency of the produced photoelectric conversion device was measured using a steady light solar simulator. Here, the photoelectric conversion efficiency was measured under conditions where the light irradiation intensity on the light receiving surface of the photoelectric conversion device was 100 mW / cm ² and the air mass (AM) was 1.5. Note that the photoelectric conversion efficiency indicates the rate at which sunlight energy is converted into electric energy in the photoelectric conversion device. Here, the value of the electric energy output from the photoelectric conversion device is the sun incident on the photoelectric conversion device. Divided by the value of the energy of light and derived by multiplying by 100.

  As a result of the photoelectric conversion efficiency measurement, as shown in Table 1, sample No. having an intermediate layer was obtained. The photoelectric conversion efficiencies of 1 to 3 are 12.1%, 12.8%, and 13.4%, respectively. 4 was found to be higher than 11.5%.

1: Substrate 2: First electrode layer 3: Intermediate layer 4: I-III-VI group compound semiconductor layer (first semiconductor layer)
5: Second semiconductor layer 6: Second electrode layer 7: Connection conductor 8: Current collecting electrode 9: Third electrode layer 11: Photoelectric conversion device

Claims (3)

An electrode layer;
An I-III-VI group compound semiconductor layer containing a gallium element located on the electrode layer;
A plurality of intermediate layers that are arranged independently at the interface between the electrode layer and the I-III-VI group compound semiconductor layer and that contain more gallium and oxygen elements than the I-III-VI group compound semiconductor layer; A photoelectric conversion device comprising:   The photoelectric conversion device according to claim 1, wherein the I-III-VI group compound semiconductor layer further contains an indium element.   The photoelectric conversion device according to claim 1, wherein the intermediate layer has an amorphous or microcrystalline structure.

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