JP2012109559A - Photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion device with high photoelectric conversion efficiency.SOLUTION: A photoelectric conversion device comprises: a first semiconductor layer having a compound semiconductor containing a group I element, a group III element, and a group VI element; and a second semiconductor layer that is disposed on the first semiconductor layer and forms a pn junction with the first semiconductor layer. The average molar concentration of the group III element in the first semiconductor layer near the second semiconductor layer is smaller than that in the first semiconductor layer.

Description

  The present invention relates to a photoelectric conversion device.

  Some solar cells use a photoelectric conversion device including a light absorption layer made of a chalcopyrite-based I-III-VI group compound semiconductor such as CIGS. In this photoelectric conversion device, for example, a back electrode is formed on a substrate, and a light absorption layer made of an I-III-VI group compound semiconductor is formed on the back electrode. Further, a transparent conductive film made of ZnO or the like is formed on the light absorption layer via a buffer layer made of ZnS, CdS, or the like (for example, see Patent Document 1).

JP 2000-156517 A

  In the chalcopyrite-based photoelectric conversion device, the light-absorbing layer made of the I-III-VI group compound semiconductor partially generates a different phase between the Group I element and the Group VI element inside the light-absorbing layer, A short circuit may occur due to the generation of a heterogeneous phase.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to improve the photoelectric conversion efficiency by reducing the generation of a different phase between the group I and the group VI in the light absorption layer.

  A photoelectric conversion device according to an embodiment of the present invention includes a first semiconductor layer having a compound semiconductor containing a group I element, a group III element, and a group VI element, and the first semiconductor layer disposed on the first semiconductor layer, And a second semiconductor layer forming a pn junction together with the first semiconductor layer. In this embodiment, the first semiconductor layer has a smaller group III element molar concentration in the vicinity of the second semiconductor layer than an average molar concentration of the group III element in the first semiconductor layer. .

  According to the photoelectric conversion device of one embodiment of the present invention, the molarity of the group III element in the first semiconductor layer in the vicinity of the second semiconductor layer is higher than the average molar concentration of the group III element in the first semiconductor layer. Since the concentration is smaller, at least one of the group I element and the group VI element in the first semiconductor layer other than the vicinity of the second semiconductor layer can be relatively reduced. Therefore, in the present embodiment, while maintaining the quality of the pn junction at the interface between the second semiconductor layer and the first semiconductor layer, at least one of the group I element and the group VI element in the first semiconductor layer is maintained. By reducing the amount, it is possible to reduce the heterogeneous formation between the group I element and the group VI element. As a result, in this embodiment, the photoelectric conversion efficiency can be improved.

It is a perspective view which shows an example of embodiment of the photoelectric conversion apparatus of this invention. It is sectional drawing which shows an example of embodiment of the photoelectric conversion apparatus of this invention.

  Hereinafter, embodiments of the photoelectric conversion device of the present invention will be described in detail with reference to the drawings.

  As shown in FIGS. 1 and 2, the photoelectric conversion device 10 according to an embodiment of the present invention includes a substrate 1, a first electrode layer 2, a light absorption layer 3 corresponding to a first semiconductor layer, A buffer layer 4 corresponding to the second semiconductor layer and a second electrode layer 5 are included.

  As shown in FIG. 1, a plurality of photoelectric conversion devices 10 are formed side by side, and constitute a photoelectric conversion module 11. The photoelectric conversion device 10 includes a third electrode layer 6 provided on the substrate 1 side of the light absorption layer 3 so as to be separated from the first electrode layer 2. In the adjacent photoelectric conversion devices 10, the second electrode layer 5 and the third electrode layer 6 are electrically connected by a connection conductor 7 provided in the light absorption layer 3. The third electrode layer 6 also functions as the first electrode layer 2 of the adjacent photoelectric conversion device 10. With this configuration, adjacent photoelectric conversion devices 10 are connected in series with each other. In one photoelectric conversion device 10, the connection conductor 7 is provided so as to divide the light absorption layer 3 and the buffer layer 4. Therefore, in the photoelectric conversion device 10, photoelectric conversion is performed between the light absorption layer 3 and the buffer layer 4 sandwiched between the first electrode layer 2 and the second electrode layer 5. Furthermore, the collector electrode 8 may be provided on the second electrode layer 5 as in the present embodiment.

  Next, each member of the photoelectric conversion device 10 will be described.

  The substrate 1 is for supporting the photoelectric conversion device 10. Examples of the material used for the substrate 1 include glass, ceramics, and resin.

  The first electrode layer 2 and the third electrode layer 6 are made of a conductor such as Mo (molybdenum), Al (aluminum), Ti (titanium), or Au (gold), and are sputtered or deposited on the substrate 1. Formed by law etc.

The light absorption layer 3 absorbs light and performs photoelectric conversion in cooperation with the buffer layer 4. The light absorption layer 3 includes a chalcopyrite compound semiconductor and is provided on the first electrode layer 2 and the third electrode layer. Here, a chalcopyrite compound semiconductor is a group I element such as a group IB element (also referred to as a group 11 element) or a group III element such as a group III-B element (also referred to as a group 13 element). And a compound semiconductor with a VI group element such as a VI-B group element (also referred to as a group 16 element) (also referred to as a CIS compound semiconductor). Examples of the chalcopyrite 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 CuInS ₂ (also referred to as CIS). Can be mentioned. Incidentally, Cu (In, Ga) and Se ₂ refers Cu, an In, mainly configured compounds from Ga and Se. Cu (In, Ga) (Se, S) ₂ refers to a compound mainly composed of Cu, In, Ga, Se and S.

  From the viewpoint of increasing the photoelectric conversion efficiency, the light absorption layer 3 may have a thickness of 1.0 to 2.5 μm, for example.

  In the present embodiment, the light absorption layer 3 has the group III element molar concentration in the vicinity of the buffer layer 4 smaller than the average molar concentration of the group III element in the light absorption layer 3. Thereby, at least one of the group I element and the group VI element in the light absorption layer 3 other than the vicinity of the buffer layer 4 can be reduced relative to the group III element. More specifically, the value obtained by dividing the amount of the group I element and the amount of the group VI element by the amount of the group III element is reduced in the light absorption layer 3 other than the vicinity of the buffer layer 4. Therefore, in the present embodiment, the amount of at least one of the group I element and the group VI element in the light absorption layer 3 is reduced while maintaining the quality of the pn junction at the interface between the buffer layer 4 and the light absorption layer 3. Therefore, it is possible to reduce the heterogeneous generation that can occur between the group I element and the group VI element.

This different phase refers to a compound different from the compound desired in the light absorption layer 3. Specifically, for example, when the group I element includes Cu (copper), the group III element includes In (indium), Ga (gallium), and the group VI element includes Se (selenium), the desired compounds are CuInSe ₂ and CuGaSe. ₂ or a mixture of CuInSe ₂ and CuGaSe ₂ . However, Cu ₂ Se having a structure different from CuInSe ₂ and CuGaSe ₂ is partially generated in the light absorption layer 3. Then, the _Cu 2 Se is out-of-phase. Since this Cu ₂ Se has conductivity, there is a case where a short circuit occurs in the light absorption layer 3 to cause a decrease in photoelectric conversion efficiency. On the other hand, in the present embodiment, the generation of Cu ₂ Se in the light absorption layer 3 is reduced by reducing at least one of Cu (Group I element) and Se (Group VI element) in the light absorption layer 3. Can do.

  On the other hand, the photoelectric conversion device 10 forms a pn junction at the interface between the light absorption layer 3 and the buffer layer 4. In this pn junction, it is desirable that the group I element, the group III element, and the group VI element have a predetermined ratio. Specifically, for example, when the group I element includes Cu, the group III element includes In, Ga, and the group VI element includes Se, in the vicinity of the pn junction, that is, in the vicinity of the buffer 4 of the light absorption layer 3, The ideal composition (molar ratio) is Cu: (In + Ga): Se = 1: 1: 2. Therefore, in the present embodiment, the concentration of various elements in the light absorption layer 3 other than the vicinity of the buffer layer 4 is controlled while maintaining the ideal molar ratio of the light absorption layer 3 in the vicinity of the buffer layer 4. In addition, the vicinity of the buffer layer 4 of the light absorption layer 3 refers to 1/10 of the thickness of the light absorption layer 3 in the stacking direction A in FIG.

  In addition, as the average molar concentration in the light absorption layer 3, when the group I element includes Cu, the group III element includes In, Ga, and the group VI element includes Se, for example, Cu is 22 to 24 mol%, and In and Ga are 26-28 mol%, Se is 48-52 mol%. Further, the molar concentration of the group III element (In, Ga) in the vicinity of the buffer layer 4 of the light absorption layer 3 is 1% or more smaller than the average molar concentration of group III in the light absorption layer 3 described above.

  Furthermore, in this embodiment, when the group III element contains gallium, the molar concentration of gallium in the vicinity of the buffer layer 4 is preferably smaller than the average molar concentration of gallium in the light absorption layer 3. Therefore, in the above configuration, when indium is further included as a group III element, indium exhibits a distribution opposite to the molar concentration of gallium in the thickness direction of the light absorption layer 3. At this time, the molar concentration of gallium in the light absorption layer 3 in the vicinity of the buffer layer 4 may be about 0.5 to 2.5 mol% lower than the molar concentration of gallium in the light absorption layer 3 in the portion other than the vicinity.

  With such a configuration, it is possible to change the band gap generated in the depth direction of the light absorption layer 3 (the direction opposite to the stacking direction A). As a result, carriers photoexcited by the electric field generated in the light absorption layer 3 are easily transported to the buffer layer 4 side. As a result, the short circuit current and the photoelectric conversion efficiency of the photoelectric conversion device 10 are improved.

  When the group III element contains gallium, the molar concentration of gallium in the light absorption layer 3 is from the portion of the light absorption layer 3 on the buffer layer 4 side to the portion of the light absorption layer 3 opposite to the buffer layer 4. It may be bigger. That is, the molar concentration of gallium in the light absorption layer 3 increases from the buffer layer 4 side in the depth direction of the light absorption layer 3. With such a configuration, the above-described band gap can be gradually changed, so that the short-circuit current and the photoelectric conversion efficiency are further improved.

Furthermore, in this embodiment, when the group I element contains Cu, the light absorption layer 3 should have a smaller average molar concentration of Cu in the light absorption layer 3 than the molar concentration of Cu in the vicinity of the buffer layer 4. . Thus, if the average molar concentration of Cu in the light absorption layer 3 is reduced, the production of Cu ₂ Se can be reduced. In Cu ₂ Se, since Cu and Se are bonded at a ratio of Cu: Se = 2: 1, the ratio of Cu in the light absorption layer 3 should be reduced, that is, the molar concentration of Cu should be reduced. The production of Cu ₂ Se can be reduced more efficiently than the reduction of group VI elements (Se). In such a case, the molar concentration of Cu in the vicinity of the buffer layer 4 only needs to be 1% or more of the average molar concentration of Cu in the light absorption layer 3.

  Furthermore, in this embodiment, when the VI group element contains Se, the light absorption layer 3 has a higher Se molar concentration in the vicinity of the buffer layer 4 than the average molar concentration of Se in the light absorption layer 3. Good. Thus, if the molar concentration of Se in the vicinity of the buffer layer 4 is increased, defects in the vicinity of the pn junction can be efficiently filled with Se, so that the quality of the pn junction can be improved. In such a case, a better pn junction is possible if the molar concentration of Se in the vicinity of the buffer layer 4 is 2% or more of the average molar concentration of Se in the light absorption layer 3.

  The molar concentration of various elements in the light absorption layer 3 can be measured using, for example, an energy dispersive x-ray spectroscopy (EDS) while observing the cross section with an electron microscope. Other methods include X-ray photoelectron spectroscopy (XPS), Auger Electron Spectroscopy (AES), etc. while the light absorption layer 3 is shaved in the thickness direction by etching or the like. May be. Further, the average molar concentration of the group III element in the light absorption layer 3 is determined by, for example, selecting any 10 cross sections (cross sections in the stacking direction A) of the light absorption layer 3 when measuring by any of the above methods. Measure and use the average value. The molar concentration of each element in the vicinity of the buffer layer 4 is 1/10 of the thickness of the light absorption layer 3 in the depth direction (the direction opposite to the stacking direction A) from the joint surface of the light absorption layer 3 with the buffer layer 4. In this region, any 10 cross-sections (cross-sections in the stacking direction A) may be selected and measured, and the average value thereof may be obtained.

  Such a light absorption layer 3 is produced as follows, for example. First, a first precursor is prepared by applying a raw material solution of a chalcopyrite compound containing a group I-B element, a group III-B element and a group VI-B element on a substrate 1 having a first electrode layer 2. (Step A1). Next, the first precursor is calcined (heat treatment) to form a calcined first precursor (step A2). The formation temperature of the calcined first precursor in step A2 is 250 to 350 ° C. Next, the first layer of the light absorption layer 3 is formed by heating the calcined first precursor in an inert atmosphere such as nitrogen or argon (step A3). The formation temperature of the 1st layer in this A3 process is 400-600 ° C. Next, a second precursor is formed by applying a raw material solution of a chalcopyrite compound containing an IB group element, an III-B group element, and a VI-B group element on the first layer (step A4). ). Next, the second precursor is calcined (heat treatment) in an inert atmosphere such as nitrogen or argon to form a calcined second precursor (step A5). The formation temperature of the calcined second precursor in step A5 is 250 to 350 ° C. Next, the second layer is formed by heating the second precursor in an atmosphere containing a VI-B group element or an inert atmosphere such as nitrogen or argon (step A6). The formation temperature of the 2nd layer in this A6 process is 400-600 ° C. Next, a third precursor is formed by applying a raw material solution of a chalcopyrite compound containing an IB group element, an III-B group element, and a VI-B group element on the second layer (step A7). . Next, the third precursor is calcined (heat treatment) in an inert atmosphere such as nitrogen or argon to form a calcined third precursor (step A8). The formation temperature of the calcined third precursor in step A8 is 250 to 350 ° C. Next, the third layer is formed by heating the third precursor in an atmosphere containing a VI-B group element or an inert atmosphere such as nitrogen or argon (step A9). The formation temperature of the 3rd layer in this A9 process is 400-600 ° C.

As a raw material solution used for the process mentioned above, what contains the IB group metal, the III-B group metal, the chalcogen-containing organic compound, and the Lewis basic organic solvent is preferable, for example. Such a raw material solution includes a solvent containing a chalcogen element-containing organic compound and a Lewis basic organic solvent (hereinafter, a solvent containing a chalcogen element-containing organic compound and a Lewis basic organic solvent is also referred to as a mixed solvent S). By using, a raw material solution of 6 wt% or more (total concentration of the group IB metal and group III-B metal with respect to the mixed solvent S) is obtained by dissolving the group IB metal and group III-B metal well Can be made. That is, by using such a mixed solvent S, compared with the case where a solution of a group I-B metal and a group III-B metal is prepared using only a chalcogen-containing organic compound or only a Lewis basic organic solvent. A high concentration solution can be obtained. Therefore, by forming a film-like precursor using this raw material solution, a good precursor that is relatively thick can be obtained even by a single application, and as a result, the light absorption layer 3 having a desired thickness can be easily formed. Moreover, it can be produced satisfactorily.

  The chalcogen-containing organic compound is an organic compound containing a chalcogen element. The chalcogen element refers to S (sulfur), Se (selenium), and Te (tellurium) among the VI-B group elements. When the chalcogen element is S (sulfur), examples of the chalcogen-containing organic compound include thiol, sulfide, disulfide, thiophene, sulfoxide, sulfone, thioketone, sulfonic acid, sulfonic acid ester, and sulfonic acid amide. . Preferably, thiol, sulfide, disulfide and the like are preferable from the viewpoint that a metal solution can be favorably produced by forming a complex with a metal. In particular, those having a phenyl group are preferred from the viewpoint of enhancing the coating property. As what has such a phenyl group, thiophenol, diphenyl sulfide, etc. and derivatives thereof are mentioned, for example.

  When the chalcogen element is Se, examples of the chalcogen-containing organic compound include selenol, selenide, diselenide, selenoxide, selenone and the like. Preferably, from the viewpoint that a metal solution can be satisfactorily formed by forming a complex with a metal, serer, selenide, diselenide and the like are preferable. In particular, those having a phenyl group are preferred from the viewpoint of enhancing the coating property. Examples of those having such a phenyl group include phenyl selenol, phenyl selenide, diphenyl diselenide and the like and derivatives thereof.

  When the chalcogen element is Te, examples of the chalcogen-containing organic compound include tellurol, telluride, ditelluride, and the like.

  A Lewis basic organic solvent is an organic solvent that can be a Lewis base. Examples of the Lewis basic organic solvent include pyridine, aniline, triphenylphosphine, and derivatives thereof. In particular, those having a boiling point of 100 ° C. or higher are preferable from the viewpoint of improving the coating property.

  Preferably, the group IB metal and the chalcogen-containing organic compound are chemically bonded, the group III-B metal and the chalcogen-containing organic compound are chemically bonded, and the chalcogen-containing metal The element-containing organic compound and the Lewis basic organic solvent are preferably chemically bonded. Thereby, a higher concentration raw material solution of 8 wt% or more can be produced.

Chemical bond between group IB metal and chalcogen-containing organic compound, chemical bond between group III-B metal and chalcogen-containing organic compound, and chemical bond between chalcogen-containing organic compound and Lewis basic organic solvent Is a chemical bond such as a coordinate bond between a IB group metal and a chalcogen element in a chalcogen element-containing organic compound, and a coordination between a III-B metal and a chalcogen element in the chalcogen element-containing organic compound. Chemical bonds such as coordinate bonds, and chemical bonds such as coordinate bonds between chalcogen elements and Lewis basic organic solvents in chalcogen-containing organic compounds, such as NMR (NMR: Nuclear Magnetic Resonance). ) Method can be confirmed. And according to this method, the chemical bond between the group IB metal and the chalcogen-containing organic compound can be detected as a peak shift of multinuclear NMR of the chalcogen element. Moreover, the chemical bond between the III-B group metal and the chalcogen-containing organic compound can be detected as a peak shift in multinuclear NMR of the chalcogen element. Moreover, the chemical bond between the chalcogen-containing organic compound and the Lewis basic organic solvent can be detected as a peak shift derived from the organic solvent. Preferably, the number of moles of the chemical bond between the group IB metal and the chalcogen-containing organic compound is 0.1 to 10 times the number of moles of the chemical bond between the chalcogen-containing organic compound and the Lewis basic organic solvent. It is good to be in the range.

  The mixed solvent S is preferably a combination that becomes liquid at room temperature from the viewpoint of handleability. The amount of the chalcogen-containing organic compound is preferably 0.1 to 10 times that of the Lewis basic organic solvent. Thus, a chemical bond between the group IB metal and the chalcogen element-containing organic compound, a chemical bond between the group III-B metal and the chalcogen element-containing organic compound, and the chalcogen element-containing organic compound and the Lewis basic organic solvent Thus, a high concentration of Group I-B metal and Group III-B metal solution can be obtained.

  As a method of preparing a solution by dissolving the Group IB metal and the Group III-B metal in the mixed solvent S, the group IB metal and the Group III-B metal are directly dissolved in the mixed solvent S. Good. In addition, any of the IB group metal and the III-B group metal may be a metal salt. From the viewpoint of suppressing impurities other than the components of the I-III-VI compound semiconductor from remaining in the light absorption layer 3, it is preferable to directly dissolve the Group IB metal and the Group III-B metal in the mixed solvent S. . Note that the fact that the Group I-B metal and the Group III-B metal are directly dissolved in the mixed solvent S means that a single metal ingot or alloy ingot is directly mixed into the mixed solvent S and dissolved. . As a result, there is no need for an extra step of dissolving a single metal ingot or alloy ingot into another compound (for example, a metal salt such as chloride) and then dissolving it in a solvent, thus simplifying the process. In addition, it is possible to suppress the inclusion of elements other than the elements constituting the light absorption layer 3 and increase the purity of the light absorption layer 3.

  The group IB metal is a group IB metal such as Cu (copper) or Ag (silver). The IB group metal may be one element or two or more elements. In the case of two or more elements, a method for preparing a solution by dissolving a group IB metal in the mixed solvent S is to mix a mixture of two or more group IB metals in the mixed solvent S at a time. It may be dissolved. Or you may mix these, after dissolving the IB group metal of each element in the said mixed solvent S, respectively.

  The group III-B metal is a group III-B metal such as Ga (gallium) or In (indium). The group III-B metal may be one element or two or more elements. In the case of two or more elements, as a method of preparing a solution by dissolving a group III-B metal in the mixed solvent S, a mixture of two or more group III-B metals is mixed into the mixed solvent S at a time. It may be dissolved. Alternatively, the III-B group metals of each element may be dissolved in the mixed solvent S and then mixed.

In this embodiment, the moles of the group I element, group III element, and group VI element in the light absorption layer 3 are changed by changing the composition of the raw material solution used in each of the steps A1, A4, and A7. The concentration is controlled. Specifically, the magnitude relationship of the molar concentration of the raw material solution used in each step of the group III element is A7 step <A4 step <A1 step. Moreover, the magnitude relationship of the molar concentration of the raw material solution used for each process of a group I element and a group VI element is A1 process <A4 process <A7 process. Thus, the molar concentration of various elements in the stacking direction of the light absorption layer 3 can be adjusted by properly using the raw material solution in which the molar concentration of various elements is adjusted in each step. Therefore, when the concentration of the group III element indium and gallium is changed along the stacking direction A of the light absorption layer 3, if the molar concentration of indium and gallium in the raw material solution used in each step is appropriately adjusted, Good.

  In addition, although the manufacturing method mentioned above has illustrated by the light absorption layer 3 which consists of a three-layer semiconductor layer through A1-A9 process, you may produce the light absorption layer 3 by laminating | stacking more semiconductor layers. . In this case, the raw material solution is so arranged that the semiconductor layer provided on the buffer layer 4 side than the semiconductor layer on the substrate 1 side has a higher molar concentration of group I and VI elements and a lower molar concentration of group III elements. What is necessary is just to prepare.

  Note that the light absorption layer 3 may be manufactured not only by the above-described method of applying the raw material solution but also by using, for example, a vapor deposition method. At this time, the semiconductor layer provided on the buffer layer 4 side rather than the semiconductor layer on the substrate 1 side has various molar concentrations of, for example, a group I element and a group VI element and a group III element. What is necessary is just to control the quantity of various elements by changing the vapor deposition rate of an element.

The photoelectric conversion device 10 uses the semiconductor layer as the light absorption layer 3, and the buffer layer 4 is formed on the light absorption layer 3. The buffer layer 4 is a layer that performs a heterojunction with the light absorption layer 3. Moreover, since the light absorption layer 3 is a p-type semiconductor, the buffer layer 4 is an n-type semiconductor. Preferably, from the viewpoint of reducing leakage current, the buffer layer is a layer having a resistivity of 1 Ω · cm or more. Examples of the buffer layer 4 include CdS, ZnS, ZnO, In ₂ S ₃ , In (OH, S), (Zn, In) (Se, OH), and (Zn, Mg) O. It is formed by a chemical bath deposition (CBD) method or the like. In (OH, S) refers to a compound mainly composed of In, OH, and S. (Zn, In) (Se, OH) refers to a compound mainly composed of Zn, In, Se, and OH. (Zn, Mg) O refers to a compound mainly composed of Zn, Mg and O. In order to increase the absorption efficiency of the light absorption layer 3, the buffer layer 4 preferably has a light transmittance with respect to the wavelength region of light absorbed by the light absorption layer 3.

  When the buffer layer 4 contains indium, the second electrode layer 5 preferably contains indium oxide. When the second electrode layer 5 contains indium oxide, it can have high transparency and high conductivity. Furthermore, when the buffer layer 4 contains indium, the buffer layer 4 and the second electrode layer 5 contain the same element, and a change in conductivity due to mutual diffusion of elements between layers can be suppressed. The light absorption layer 3 is preferably a chalcopyrite-based material containing indium, the buffer layer 4 preferably contains indium, and the second electrode layer 5 preferably contains indium oxide. In such a form, the light absorption layer 3, the buffer layer 4, and the second electrode layer 5 all contain indium, so that changes in conductivity and carrier concentration due to interdiffusion of elements between layers can be reduced.

  From the viewpoint of improving the moisture resistance of the photoelectric conversion device 10, the buffer layer 4 preferably contains a III-VI group compound as a main component. The III-VI group compound is a compound of a III-B group element and a VI-B group element. The phrase “containing a III-VI group compound as a main component” means that among the compounds constituting the buffer layer 4, the III-VI group compound is 50 mol% or more, more preferably 80 mol% or more. Furthermore, from the viewpoint of improving the moisture resistance of the photoelectric conversion device 10, among the metal elements constituting the buffer layer 4, the Zn element should be 50 atomic% or less, more preferably 20 atomic% or less.

  The buffer layer 4 has a thickness of 10 to 200 nm, preferably 100 nm or more. Thereby, the fall of the photoelectric conversion efficiency in high temperature, high humidity conditions can be suppressed especially effectively.

The second electrode layer 5 is a 0.05 to 3.0 μm transparent conductive film such as ITO or ZnO. The second electrode layer 5 is formed by sputtering, vapor deposition, chemical vapor deposition (CVD), or the like. The second electrode layer 5 is a layer having a resistivity lower than that of the buffer layer 4, and is for taking out charges generated in the light absorption layer 3. From the viewpoint of taking out charges well, it is preferable that the resistivity of the second electrode layer 5 is less than 1 Ω · cm and the sheet resistance is 50 Ω / □ or less.

  In order to increase the absorption efficiency of the light absorption layer 3, the second electrode layer 5 preferably has a light transmittance with respect to the absorption light of the light absorption layer 3. The second electrode layer 5 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 prevention effect and the light scattering effect and further transmitting the current generated by the photoelectric conversion. Thickness is preferred.

  From the viewpoint of improving the moisture resistance of the photoelectric conversion device 10, it is preferable that the second electrode layer 5 contains a III-VI group compound as a main component. The III-VI group compound as a main component means that the compound constituting the second electrode layer 5 is a III-VI group compound (when there are plural types of III-VI group compounds, the total) Is 50 mol% or more, more preferably 80 mol% or more. Further, from the viewpoint of improving the moisture resistance of the photoelectric conversion cell 10, among the metal elements constituting the second electrode layer 5, the Zn element should be 50 atomic% or less, more preferably 20 atomic% or less. .

In the photoelectric conversion device 10, a portion where the buffer layer 4 and the second electrode layer 5 are combined, that is, a portion sandwiched between the light absorption layer 3 and the current collecting electrode 8 contains a III-VI group compound as a main component. It is preferable. The III-VI group compound as a main component means that among the compounds constituting the combined portion of the buffer layer 4 and the second electrode layer 5, a III-VI group compound (a plurality of types of III- When there is a group VI compound, the total) is 50 mol% or more, more preferably 80 mol% or more. Further, from the viewpoint of improving the moisture resistance of the photoelectric conversion cell 20, among the metal elements constituting the combined portion of the buffer layer 4 and the second electrode layer 5, the Zn element is more preferably 50 atomic% or less. Is preferably 20 atomic% or less.

  A plurality of photoelectric conversion devices 10 can be arranged and electrically connected to form a photoelectric conversion module 11. In order to easily connect adjacent photoelectric conversion devices 10 in series, as shown in FIG. 1, the photoelectric conversion device 10 is provided on the substrate 1 side of the light absorption layer 3 so as to be separated from the first electrode layer 2. The third electrode layer 6 is provided. The second electrode layer 5 and the third electrode layer 6 are electrically connected by a connection conductor 7 provided in the light absorption layer 3.

  The connection conductor 7 is preferably formed and integrated at the same time when the second electrode layer 5 is formed. Thereby, the process can be simplified and the reliability of electrical connection with the second electrode layer 5 can be improved.

  The connection conductor 7 is formed so as to connect the second electrode layer 5 and the third electrode layer 6 and to divide each light absorption layer 3 of the adjacent photoelectric conversion device 10. With such a configuration, photoelectric conversion can be performed satisfactorily in the adjacent light absorption layers 3 and current can be taken out in series connection.

  The current collecting electrode 8 has a function of reducing the electric resistance of the second electrode layer 5. From the viewpoint of increasing light transmittance, the thickness of the second electrode layer 5 is preferably as thin as possible, but if it is thin, the conductivity is lowered. However, since the current collecting electrode 8 is provided on the second electrode layer 5, the current generated in the light absorption layer 3 can be taken out efficiently. As a result, the power generation efficiency of the photoelectric conversion device 10 can be increased.

For example, as shown in FIG. 1, the collector electrode 8 is formed in a linear shape from one end of the photoelectric conversion device 10 to the connection conductor 7. Thereby, after the electric charge generated by the photoelectric conversion of the light absorption layer 3 is collected to the current collecting electrode 8 through the second electrode layer 5, the electric charge is satisfactorily conducted to the adjacent photoelectric conversion device 10 through the connection conductor 7. Can be made. Therefore, by providing the current collecting electrode 8, the current generated in the light absorption layer 3 can be efficiently extracted even if the second electrode layer 5 is thinned. As a result, power generation efficiency can be increased.

  The collector electrode 8 preferably has a width of 50 to 400 μm from the viewpoint of suppressing light from being blocked to the light absorption layer 3 and having good conductivity. The current collecting electrode 8 may have a plurality of branched portions.

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

  The current collecting electrode 8 preferably contains solder. Thereby, while being able to raise the tolerance with respect to a bending stress, resistance can be reduced more. The current collecting electrode 8 preferably includes two or more kinds of metals having different melting points, melts at least one kind of metal, and is heated and cured at a temperature at which the other at least one kind of metal is not melted. As a result, the metal having a low melting point is melted and the current collecting electrode 8 is densified, the resistance can be lowered, and the molten metal is prevented from spreading when heated and hardened by the metal having a high melting point. can do.

  The collector electrode 8 is preferably provided so as to reach the outer peripheral end of the light absorption layer 3 in plan view. In such a form, the current collecting electrode 8 protects the outer peripheral portion of the light absorption layer 3, suppresses chipping in the outer peripheral portion of the light absorption layer 3, and favors photoelectric conversion also in the outer peripheral portion of the light absorption layer 3. It can be carried out. Further, the current generated at the outer peripheral portion of the light absorption layer 3 can be efficiently taken out by the collecting electrode 8 reaching the outer peripheral end portion. As a result, in such a form, the photoelectric conversion efficiency can be increased.

  Since the outer peripheral portion of the light absorbing layer 3 can be protected by the current collecting electrode 8 that reaches the outer peripheral end portion of the light absorbing layer 3 in this way, it is provided between the first electrode layer 2 and the current collecting electrode 8. The total thickness of the members can be reduced. Therefore, the number of members can be reduced, and the manufacturing steps can be shortened. The total thickness of the members provided between the first electrode layer 2 and the current collecting electrode 8 (the total thickness of the light absorption layer 3, the buffer layer 4, and the second electrode layer 5) is 1.06. It should just be -3.2 micrometers. Specifically, the thickness of the light absorption layer 3 is 1.0 to 2.5 μm, the thickness of the buffer layer 4 is 0.01 to 0.2 μm, and the thickness of the second electrode layer 5 is 0.05 to 0.5 μm. And it is sufficient.

  Further, at the outer peripheral end of the light absorbing layer 3 reaching the current collecting electrode 8, the end surface of the current collecting electrode 8, the end surface of the second electrode layer 5, and the end surface of the light absorbing layer 3 are flush with each other. Is preferred. Thereby, the electric current photoelectrically converted at the outer peripheral end of the light absorption layer 3 can be taken out satisfactorily. It is preferable that the current collecting electrode 8 reaches the outer peripheral end of the light absorption layer 3 in plan view. Thereby, the progress of chipping with the outer peripheral end portion of the light absorption layer 3 as a base point can be reduced. At this time, the distance between the outermost outer peripheral end of the light absorption layer 3 and the end of the current collecting electrode 8 may be about 1000 μm or less.

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

1: Substrate 2: First electrode layer 3: Light absorption layer (first semiconductor layer)
4: Buffer layer (second semiconductor layer)
5: Second electrode layer 6: Third electrode layer 7: Connection conductor 8: Current collecting electrode 10: Photoelectric conversion device 11: Photoelectric conversion module

Claims (5)

A first semiconductor layer having a compound semiconductor containing a group I element, a group III element, and a group VI element;
A second semiconductor layer disposed on the first semiconductor layer and forming a pn junction with the first semiconductor layer;
The photoelectric conversion device, wherein the first semiconductor layer has a smaller group III element molar concentration in the vicinity of the second semiconductor layer than an average molar concentration of the group III element in the first semiconductor layer.   2. The photoelectric device according to claim 1, wherein the group III element includes gallium, and the molar concentration of the gallium in the vicinity of the second semiconductor layer is smaller than the average molar concentration of the gallium in the first semiconductor layer. Conversion device.   The molar concentration of the gallium in the first semiconductor layer is changed from a portion of the first semiconductor layer on the second semiconductor layer side to a portion of the first semiconductor layer opposite to the second semiconductor layer. The photoelectric conversion device according to claim 2, wherein the photoelectric conversion device increases toward the front.   The Group I element includes copper, and the first semiconductor layer has a lower average molar concentration of copper in the first semiconductor layer than a molar concentration of copper in the vicinity of the second semiconductor layer. The photoelectric conversion device according to any one of claims 1 to 3, wherein the photoelectric conversion device is provided. The group VI element includes selenium, and the first semiconductor layer has a higher molar concentration of the selenium in the vicinity of the second semiconductor layer than an average molar concentration of the selenium in the first semiconductor layer. The photoelectric conversion device according to any one of claims 1 to 4, wherein the photoelectric conversion device is provided.

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