JP6015994B2 - Optical element and manufacturing method thereof - Google Patents

Description

  The present invention relates to an optical element and a manufacturing method thereof, and more particularly to an optical element using a chalcogenide (including chalcopyrite, kesterite, etc.)-Based material as a light absorbing layer or a light emitting layer and a manufacturing method thereof.

  Optical elements (solar cells, light sensors, light emitting elements, light receiving elements, etc.) using chalcogenide (including chalcopyrite, kesterite, etc.) materials as light absorbing layers or light emitting layers are highly efficient and cost effective optical elements. Has attracted attention as. It has been reported that the addition of a small amount of an alkali metal is useful for improving the characteristics particularly for optical elements using a chalcopyrite material as a light absorption layer among chalcogenide materials (for example, non-patent literature). 1).

  Soda lime glass (SLG) generally used as a substrate contains alkali metals such as sodium (Na) and potassium (K). Therefore, in the case of an optical element in which a metal back electrode and a light absorption layer (or light emitting layer) using a chalcogenide-based material are laminated on the SLG substrate, the alkali metal of the SLG substrate passes through the metal back electrode by natural diffusion, and light Supplied to the absorption (light emission) layer. By using this method, the alkali metal can be added to the light absorption layer or the light emitting layer using the chalcogenide-based material very easily, and the characteristics can be improved.

However, in recent years, oxide layers (silicon oxide: SiO ₂ , titanium oxide: TiO ₂ , zinc oxide: ZnO, etc.) such as a transparent conductive film have been developed for the purpose of multifunctionalization of the back surface structure of optical elements (reflection mirrors, texture formation, etc.). Alumina: Al ₂ O ₃ , tin oxide: SnO _2, etc.) are inserted between the SLG substrate and the light absorption layer (or light emitting layer) using a chalcogenide-based material. However, in the case of this structure, the oxide layer functions as an alkali barrier, and the alkali metal supplied by natural diffusion from the SLG substrate cannot sufficiently pass through the oxide layer, and a chalcogenide-based material is used. The supply of alkali metal to the light absorbing layer (or light emitting layer) was hindered. It is known that the oxide layer has a function as an alkali barrier (see, for example, Patent Document 1).

  Therefore, in order to solve the above problem, one of the following two countermeasure methods is mainly used. As shown in the element cross-sectional view of FIG. 14, the first countermeasure method is an oxide layer (single layer or multilayer) between the substrate 1 and the light absorption layer (or light emitting layer) 3 using a chalcogenide-based material. When manufacturing a structure in which 2 is inserted (including a three-dimensional structure), an alkali metal sodium (Na) is added to the black circle during the formation of the light absorbing layer (or light emitting layer) 3 using a chalcogenide-based material. In the form of sodium fluoride (NaF) or the like (see, for example, Non-Patent Document 2). It should be noted that sodium (Na) may be added in the form of sodium fluoride (NaF) or the like in steps before and after the step of forming the light absorption layer (or light emitting layer) 3 using a chalcogenide-based material.

Further, as shown in the device cross-sectional view of FIG. 15, the second countermeasure method is an oxide layer (single layer or single layer) between the substrate 1 and the light absorption layer (or light emitting layer) 5 using a chalcogenide-based material. This is a method of forming an alkali metal supply layer 4 immediately below the light absorption layer (or light emitting layer) 5 in a structure in which a multilayer structure (including a three-dimensional structure) 2 is inserted (for example, see Non-Patent Document 3). That is, in this case, a structure is obtained in which the oxide layer 2, the alkali metal supply layer 4, and the light absorption layer (or light emitting layer) 5 using a chalcogenide-based material are stacked on the substrate 1 in this order. As the alkali metal supply layer 4, a silicate glass thin film and molybdenum (Mo) to which an alkali metal is added are used. According to the second countermeasure method, the alkali metal from the alkali metal supply layer 4 is added to the light absorption layer (or light emitting layer) 5 using the chalcogenide material.
In some cases, a layer (metal film or the like) that does not prevent the diffusion of alkali metal is inserted between the alkali metal supply layer 4 and the light absorption layer (or light emitting layer) 5 using the chalcogenide-based material.

JP-A-8-53760

MAContreras, et al., “On the role of Na and Modifications to Cu (In, Ga) Se2 absorber materials using thin MF (M = Na, K, Cs) precursor layers”, Proceedings of the 26th IEEE Photovoltaic Specialists Conference, Anaheim (IEEE, New York, 1997), p.359. D. Rudmann, et al., “Na incorporation into Cu (In, Ga) Se2 for high efficiency flexible solar cells on polymer foiles”, J. Appl. Phys 97, (2005) 084903. Shogo Ishizuka, et al., “Na-induced variations in the structural, optical, and electrical properties of Cu (In, Ga) Se2 thin films”, J. Appl. Phys, 106 (2009) 034908.

  However, the above first countermeasure method requires a fine optimization of the supply timing and supply amount of Na, which is an alkali metal, and a conventionally used light absorption layer (or light emitting layer) film forming method (three steps). Method, selenization method, etc.) cannot be used as they are, and there is a problem that improvements must be made.

  In the second countermeasure method, when the oxide layer 2 is a transparent conductive film and the alkali metal supply layer 4 is an insulator such as a silicate glass thin film, the conductivity of the transparent conductive film is impaired. There is a problem. Moreover, when the oxide layer 2 is a transparent conductive film and the alkali metal supply layer 4 is made of a material that supplies an alkali metal such as an alkali metal-added Mo, there is a problem that the transparency of the transparent conductive film is impaired.

  The present invention has been made in view of the above points, and can use a known film-forming method of a light-absorbing layer (or light-emitting layer) using a chalcogenide-based material as it is, and an oxide layer (such as a transparent conductive film). It is an object of the present invention to provide an optical element that does not affect the conductivity and transparency at the boundary between the light-absorbing layer (or light-emitting layer) using a chalcogenide-based material and a method for manufacturing the same.

In order to achieve the above object, the optical element of the present invention includes a chalcogen that requires addition of an oxide layer having a single layer, a multilayer structure, or a three-dimensional structure, and an alkali metal above a substrate that supplies the alkali metal. In an optical element laminated in the order of a light-absorbing layer or a light-emitting layer made of a fluoride-based material, a metal film having a function as an alkali metal diffusion promoting layer is inserted between an alkali metal substrate and an oxide layer. The structure is characterized in that the metal film promotes diffusion in the oxide layer of the alkali metal from the substrate supplying the alkali metal and supplies the alkali metal to the light absorption layer or the light emitting layer. .
Here, the substrate for supplying the alkali metal is an alkali metal-containing substrate itself or a substrate having a structure in which an alkali metal-containing film is formed on a base substrate. Further, the substrate for supplying the alkali metal and the metal film may be a metal film-containing substrate having a structure in which a metal substrate itself containing an alkali metal or a metal layer containing an alkali metal is formed on a base substrate. .

In order to achieve the above object, the optical element manufacturing method of the present invention includes a film forming step of forming a metal film on a substrate to which an alkali metal is supplied, and an upper surface of the formed metal film. And an oxide layer forming step for forming an oxide layer having a single layer, a multilayer structure, or a three-dimensional structure, and a chalcogenide-based material that requires addition of an alkali metal on the formed oxide layer. A layer forming step for forming a light absorbing layer or a light emitting layer, and a metal film formed between the substrate and the oxide layer is used to promote diffusion of alkali metal from the substrate into the oxide layer. An optical element having a structure that functions as a diffusion promoting layer and supplies an alkali metal from a substrate to an optical absorption layer or an emission layer through an oxide layer is manufactured.
Here, the film forming step and the oxide layer forming step supply the alkali metal having a structure in which a metal substrate itself containing an alkali metal or a metal layer containing an alkali metal is formed on a base substrate. The oxide layer may be formed on a metal film combined substrate having both the substrate and the metal film.

  According to the present invention, even in an optical element having a structure in which an oxide layer is introduced between an alkali metal-containing layer and a chalcogenide-based light absorption layer (or light-emitting layer), the chalcogenide-based light absorption layer (or light-emitting layer) Alkali metal can be sufficiently supplied to the substrate, and a known film forming method (three-stage method, selenization method, etc.) of the light absorption layer or the light emitting layer can be used as it is. Further, according to the present invention, it is possible to manufacture an optical element that does not deteriorate the conductivity and transparency at the boundary between the oxide layer (transparent conductive film or the like) and the light absorbing layer or the light emitting layer.

1 is a schematic cross-sectional view of a first embodiment of an optical element according to the present invention. It is a schematic sectional drawing of 2nd Embodiment of the optical element which concerns on this invention. It is a schematic sectional drawing of 3rd Embodiment of the optical element which concerns on this invention. It is a schematic sectional drawing of 4th Embodiment of the optical element which concerns on this invention. It is a schematic sectional drawing of 5th Embodiment of the optical element which concerns on this invention. It is a schematic sectional drawing of 6th Embodiment of the optical element which concerns on this invention. It is element sectional drawing in each process of one Embodiment of the manufacturing method of the optical element which concerns on this invention. It is sectional drawing of Example 1 of the optical element which concerns on this invention, and sectional drawing of an example of a common transparent conductive film utilization CIGS solar cell. It is a figure which shows Na concentration distribution in the CIGS layer of the solar cell of the general structure by secondary ion mass spectrometry (SIMS). It is a figure which shows Na density distribution in the CIGS layer of the solar cell of the general transparent conductive film introduction | transduction structure by secondary ion mass spectrometry (SIMS). It is a figure which shows Na density distribution in the CIGS layer of the solar cell by the optical element of this invention by secondary ion mass spectrometry (SIMS). It is a figure which shows Na density | concentration distribution in the CIGS layer evaluated with the electron beam microanalyzer (EPMA). It is a figure which shows the current-voltage characteristic of the solar cell of a present Example contrasted with the current-voltage characteristic of a general solar cell. It is element | device sectional drawing for description of the conventional 1st countermeasure method. It is element sectional drawing for description of the conventional 2nd countermeasure method.

(First embodiment)
FIG. 1 shows a schematic cross-sectional view of a first embodiment of an optical element according to the present invention. In the figure, an optical element 10 has a structure in which a metal film 12, an oxide layer 13, and a chalcogenide-based light absorption (light emission) layer 14 are laminated in this order on an alkali metal-containing layer 11 such as an SLG substrate. The metal film 12 is a thin film made of a metal such as molybdenum (Mo) or tungsten (W). The oxide layer 13 is an example of a film that hardly diffuses alkali metal, and is, for example, a transparent conductive film. The oxide layer 13 includes silicon oxide (SiO ₂ ), titanium oxide (TiO ₂ ), zinc oxide (ZnO), alumina (Al ₂ O ₃ ), tin oxide (SnO ₂ ), indium tin oxide (ITO), and the like. Used. In FIG. 1, the oxide layer 13 is a single layer, but may be a multilayer structure or a three-dimensional structure as will be described later.

  The chalcogenide-based light absorption layer (or light-emitting layer) 14 is a light-absorption layer (or light-emitting layer) using a chalcogenide-based material that requires the addition of an alkali metal, and the optical element 10 is a solar cell, a photosensor, a light-receiving layer. When used as an element or the like, it is used as a light absorbing layer, and when used as a light emitting element, it is used as a light emitting layer. In the present specification, the “light absorption layer (or light emitting layer)” is hereinafter referred to as “light absorption (light emitting) layer” for the sake of simplicity.

  The optical element 10 has a structure in which an oxide layer 13 is inserted between an alkali metal-containing layer 11 and a chalcogenide-based light absorption (light emitting) layer 14, and a metal is interposed between the alkali metal-containing layer 11 and the oxide layer 13. The structure in which the membrane 12 is inserted is characteristic. The metal film 12 functions as an alkali metal diffusion promoting layer that promotes diffusion of alkali metal (for example, Na) supplied from the alkali metal-containing layer 11 by natural diffusion in the oxide layer 13. Thereby, even if the oxide layer 13 is a material in which the alkali metal is difficult to diffuse, the alkali metal schematically shown by a black circle in FIG. A sufficient amount is supplied to the chalcogenide-based light absorption (light emission) layer 14 through the oxide layer 13. In addition, the verification experiment result about the alkali metal in the oxide layer 13 being accelerated | stimulated by the metal film 12 is mentioned later.

  According to the optical element 10 of the present embodiment, the metal film 12 has a structure in which the oxide layer 13 is introduced between the alkali metal-containing layer 11 and the chalcogenide-based light absorption (light emission) layer 14 for multifunctional purposes. Has a function as an alkali metal diffusion accelerating layer that promotes diffusion of alkali metal in the oxide layer 13, so that the alkali metal can be supplied to the chalcogenide-based light absorption (light emitting) layer 14. The method (alkali metal supply method by natural diffusion from a soda-lime glass substrate) can be used as it is. Therefore, according to the optical element 10 of this embodiment, a known chalcogenide-based light absorption (light emission) layer forming method (three-stage method, selenization method, etc.) can be used as it is. In addition, since the metal film 12 is formed under the oxide layer 13 such as a transparent conductive film, the metal film 12 has conductivity at the boundary between the chalcogenide-based light absorption (light emission) layer 14 and the oxide layer 13. There is no effect that would degrade transparency.

  In the optical element 10, a thin metal layer (electrode) may be formed between the chalcogenide-based light absorption (light emission) layer 14 and the oxide layer 13 in order to improve ohmic characteristics. In the optical element having this structure, it is possible to reduce the cost for electrode formation by replacing part or all of the electrodes with the oxide layer 13. Moreover, the crustal abundance of zinc (Zn) is higher than the electrode material Mo generally used as the electrode. Therefore, when part or all of the electrode made of Mo is replaced with zinc oxide (ZnO), the raw material price can be reduced.

The optical element having a structure in which a part of the electrode is replaced with an oxide layer is an oxide having a conductivity other than zinc oxide (ZnO) in which the oxide layer is a part or all of Mo as an electrode. (For example, tin oxide (SnO ₂ ), indium tin oxide (ITO), etc.) may be substituted. Also in the optical element having such a structure, since the metal film 12 has a function as an alkali metal diffusion promoting layer that promotes diffusion of alkali metal in the oxide layer, the alkali metal is converted from the alkali metal-containing layer 11 to the metal film. 12, a sufficient amount is supplied to the chalcogenide-based light absorption (light emission) layer 14 through the oxide layer and the electrode (or the oxide layer having an electrode function).
(Second Embodiment)

  FIG. 2 shows a schematic cross-sectional view of a second embodiment of the optical element according to the invention. In the figure, the same reference numerals are given to the same structural portions as those in FIG. By the way, in order to increase the effective optical path length, a direct reflecting mirror or scattering layer (aluminum (Al), silver (Ag), etc .: including nanoparticles) is directly under the chalcogenide-based light absorption (light emission) layer (may be an upper layer). When the element is formed, the elements forming the chalcogenide-based light absorption (emission) layer (especially selenium (Se) or sulfur (S)) react with the reflecting mirror or scattering layer material to cause alteration of the reflecting mirror or scattering layer material. To do. Therefore, an oxide layer such as a transparent film is inserted between the chalcogenide-based light absorption (emission) layer and the reflecting mirror or scattering layer to maintain the above-mentioned alteration while maintaining the reflecting / scattering characteristics of the reflecting mirror and scattering layer. It is done to prevent.

  However, in the case of this structure, as described above, the oxide layer such as a transparent film functions as an alkali barrier, and the alkali metal supplied from the alkali metal-containing layer cannot sufficiently pass through the oxide layer. Supply of the alkali metal to the chalcogenide-based light absorption (light emission) layer is hindered.

  Therefore, as shown in FIG. 2, the optical element 20 of the present embodiment is provided between a chalcogenide-based light absorption (light emission) layer 14 and a reflecting mirror or scattering layer (Al, Ag, etc .: including nanoparticles) 22. In an optical element in which a transparent film 23 is inserted, a metal made of a metal such as Mo or W between an alkali metal-containing layer 11 such as an SLG substrate and a reflecting mirror or scattering layer (including Al, Ag, etc .: including nanoparticles) 22 The film 21 is interposed. In this optical element 20, the oxide layer has a multilayer structure of a reflecting mirror or scattering layer 22 and a transparent film 23.

  Similar to the metal film 12 described above, the metal film 21 has a function as an alkali metal diffusion promoting layer, and a supplied alkali metal oxide having a multilayer structure of a reflecting mirror or scattering layer 22 and a transparent film 23. Promotes diffusion in the layer. For this reason, in the optical element 20, the alkali metal schematically shown by a black circle in FIG. 2 passes through the metal film 21, the reflecting mirror or scattering layer 22, and the transparent film 23 from the alkali metal-containing layer 11 as indicated by an arrow. A sufficient amount is supplied to the chalcogenide-based light absorption (light emission) layer 14.

  Therefore, when the optical element 20 is manufactured, a conventional alkali metal supply method by natural diffusion from the alkali metal-containing layer 11 to the chalcogenide-based light absorption (light emission) layer 14 can be used as it is. Therefore, according to the optical element 20 of the present embodiment, a known chalcogenide-based light absorption (light emission) layer forming method (three-stage method, selenization method, etc.) can be used as it is. Further, since the metal film 21 is formed below the transparent film 23, the metal film 21 has an effect of deteriorating the conductivity and transparency at the boundary portion between the chalcogenide-based light absorption (light emission) layer 14 and the transparent film 23. Never give.

In the optical element 20, a thin metal layer (electrode) may be formed between the chalcogenide-based light absorption (light emission) layer 14 and the transparent film 23 to improve ohmic characteristics. The same effect as above can be obtained. It is also possible to replace some or all of the above electrodes by making the transparent film 23 conductive.
(Third embodiment)

FIG. 3 shows a schematic cross-sectional view of a third embodiment of the optical element according to the invention. In the figure, the same reference numerals are given to the same structural portions as those in FIG. By the way, it is known that an oxide layer of SnO ₂ , In ₂ O ₃ , ZnO or the like can easily form a texture structure by a forming method such as chemical etching or optimization of film forming conditions (O. Kluth, et al., “Texture etched ZnO: Al coated glass substrates for silicon based thin film solar cells”, Thin Solid Films 351 (1999) 247 ± 253). By inserting this textured oxide layer as a transparent conductive film between the chalcogenide-based light absorption (emission) layer and the alkali metal-containing layer, the effective optical path length in the chalcogenide-based light absorption (emission) layer can be reduced. As a result, the light absorption rate (light emission rate) of the chalcogenide-based light absorption (light emission) layer can be improved.

  In the optical element 30 shown in FIG. 3, an oxide layer 32 having a texture structure is provided immediately below the chalcogenide light absorption (light emission) layer 33 to increase the optical path length of the chalcogenide light absorption (light emission) layer 33. In the structure, a metal film 31 made of a metal such as Mo or W is interposed between the oxide layer 32 having a texture structure and the alkali metal-containing layer 11. The oxide layer 32 is a three-dimensional structure oxide layer having a texture structure, for example, a transparent conductive film.

  Similar to the metal films 12 and 21 described above, the metal film 31 functions as an alkali metal diffusion promoting layer and is diffused in the oxide layer 32 having an alkali metal texture structure supplied from the alkali metal-containing layer 11. Promote. For this reason, in the optical element 30, the alkali metal schematically shown by a black circle in FIG. 3 passes through the metal film 31 and the oxide layer 32 having the texture structure from the alkali metal-containing layer 11 to the chalcogenide, as indicated by arrows. A sufficient amount is supplied to the system light absorption (light emission) layer 33.

  Therefore, in the optical element 30, a conventional method for supplying alkali metal by natural diffusion from the alkali metal-containing layer 11 to the chalcogenide-based light absorption (light emission) layer 33 can be used. Therefore, according to the optical element 30 of this embodiment, a known chalcogenide-based light absorption (light emission) layer forming method (three-stage method, selenization method, etc.) can be used as it is. Further, since the metal film 31 is formed immediately below the oxide layer 32 such as a transparent conductive film, the metal film 31 has conductivity and transparency at the boundary portion between the chalcopyrite light absorption layer 33 and the oxide layer 32. There is no detrimental effect.

  In the optical element 30, a thin metal layer (electrode) may be formed between the oxide layer 32 having a texture structure and the chalcogenide-based light absorption (light emission) layer 33 in order to improve ohmic characteristics. In the case of this structure, the same effect as described above can be obtained. It is also possible to replace part or all of the electrodes by giving conductivity to the oxide layer 32.

  As a modification of the optical element 30, a transparent film / reflection film is used between the oxide layer 32 having a texture structure and the chalcogenide-based light absorption (light emission) layer 33 in order to improve the reflectance on the texture surface. There is a structure for forming a reflecting mirror made of a film (Al, Ag, etc.). In the case of this structure as well, the third embodiment is achieved by providing a metal film 31 made of a metal such as Mo or W between the oxide layer 32 having a texture structure and the alkali metal-containing layer 11. The same effect can be obtained.

In this modified example, a thin metal layer (electrode) may be formed on the upper part of the reflector made of a transparent film / reflective film (Al, Ag, etc.) to improve ohmic characteristics. The same effect as above can be obtained. It is also possible to replace part or all of the electrodes by giving conductivity to the oxide layer 32.
(Fourth embodiment)

  FIG. 4 shows a schematic sectional view of a fourth embodiment of an optical element according to the invention. In the figure, the same reference numerals are given to the same structural portions as those in FIG. By the way, in silicon-based solar cells, it is known that the light absorption characteristics of solar cells are improved by the light confinement effect by producing a structure in which metal particles (Ag nanoparticles, etc.) are embedded in a transparent conductive film. Hidenori Mizuno, et al., “Light Trapping by Ag Nanoparticles Chemically Assembled inside Thin-Film Hydrogenated Microcrystalline Si Solar Celles”, Japanese Journal of Applied Physics 51 (2012) 042302.). In the chalcogenide-based material, a similar effect can be expected by producing a structure in which metal particles (Ag nanoparticles, etc.) are embedded in a transparent conductive film.

  Therefore, as shown in FIG. 4, the optical element 40 of the present embodiment is an oxide having a scattering mirror structure in which metal particles (Ag, Al, etc.) 43 are introduced directly under the chalcogenide-based light absorption (light emission) layer 14. In the optical element in which the light absorption (light emission) characteristics are improved by providing the layer 42, a metal film made of a metal such as Mo or W between the alkali metal-containing layer 11 such as an SLG substrate and the oxide layer 42 having a scattering mirror structure. 41 is interposed. The oxide layer 42 having a scattering mirror structure is an oxide layer having a multilayer structure, for example, a transparent conductive film.

  Similar to the metal films 12, 21, and 31 described above, the metal film 41 has a function as an alkali metal diffusion promoting layer, and promotes diffusion of supplied alkali metal in the oxide layer 42 having a scattering mirror structure. . For this reason, in the optical element 40, the alkali metal schematically shown by a black circle in FIG. 4 passes through the metal film 41 and the oxide layer 42 of the scattering mirror structure from the alkali metal-containing layer 11 through the chalcogenide, as indicated by arrows. A sufficient amount is supplied to the system light absorption (light emission) layer 14.

  Therefore, when the optical element 40 is manufactured, a conventional alkali metal supply method by natural diffusion from the alkali metal-containing layer 11 to the chalcogenide-based light absorption (light emission) layer 14 can be used as it is. Therefore, according to the optical element 40 of the present embodiment, a known chalcogenide-based light absorption (light emission) layer forming method (three-stage method, selenization method, etc.) can be used as it is. Further, since the metal film 41 is formed under the oxide layer 42 having the scattering mirror structure, the metal film 41 is formed at the boundary between the chalcogenide-based light absorption (light emission) layer 14 and the oxide layer 42 having the scattering mirror structure. There is no effect of deteriorating conductivity and transparency.

In the optical element 40, a thin metal layer (electrode) may be formed between the oxide layer 42 having a scattering mirror structure and the chalcogenide-based light absorption (light emission) layer 14 in order to improve ohmic characteristics. In the case of this structure, the same effect as described above can be obtained. In addition, when the oxide layer 42 having a scattering mirror structure has conductivity, it is also possible to replace part or all of the electrodes with the oxide layer 42 having a scattering mirror structure having conductivity.
(Fifth embodiment)

  FIG. 5 shows a schematic cross-sectional view of a fifth embodiment of the optical element according to the invention. In the figure, the same reference numerals are given to the same structural portions as those in FIG. The optical element 50 shown in FIG. 5 has a structure in which a metal film 51 and a light absorption (light emission) layer 52 made of an oxide are stacked in this order on the alkali metal-containing layer 11, and a chalcogenide light absorption (light emission). There is no layer. The metal film 51 is a thin film formed of a metal material such as Mo or W. Further, the light absorption (light emission) layer 52 made of an oxide is an oxide layer having a single layer structure, a multilayer structure, or a three-dimensional structure.

Similar to the metal films 12, 21, and 31 described above, the metal film 51 functions as an alkali metal diffusion promoting layer and diffuses in the light absorption (light emission) layer 52 made of supplied alkali metal oxide. Promote. For this reason, in the optical element 50, the alkali metal schematically shown by the black circles in FIG. 5 is supplied from the alkali metal-containing layer 11 to the light absorption (light emission) layer 52 made of oxide through the metal film 51, as indicated by the arrows. In the light absorption (light emission) layer 52 made of oxide, the light is also diffused in the lateral direction. In this optical element 50, the oxide layer itself is used as a light absorption (light emission) layer. When using light emission (ultraviolet light or the like) of the light absorption (light emission) layer 52 itself made of an oxide, there is a possibility that the optical response is accelerated due to a decrease in carrier lifetime due to alkali metal doping. In this optical element 50, an alkali metal supply function by natural diffusion from the alkali metal-containing layer 11 to the light absorption (light emission) layer 52 made of an oxide can be used by the alkali metal diffusion function of the metal film 51.
(Sixth embodiment)

  FIG. 6 shows a schematic cross-sectional view of a sixth embodiment of the optical element according to the invention. In the figure, the same reference numerals are given to the same structural portions as those in FIG. In the optical elements of the first to fifth embodiments described above, the metal film 12, 21, 41, or 51 is formed on the alkali metal-containing layer 11, but the optical element of the present embodiment shown in FIG. The element 55 is characterized in that a metal film combined substrate 56 in which the metal film also serves as an alkali metal-containing layer is used.

  Specifically, the metal film combined substrate 56 is a metal substrate containing an alkali metal or a substrate having a structure in which a metal layer containing an alkali metal is formed on a substrate of a base. For example, Mo, W, Al, Ag, Made of stainless steel or steel plate. The alkali metal-containing metal substrate or the metal layer containing the alkali metal functions as an alkali metal diffusion promoting layer and at the same time as an alkali metal supply layer, similarly to the metal films 12, 21, 41, and 51 described above. . For this reason, in the optical element 55, as indicated by the arrows in FIG. 6, the alkali metal schematically shown by the black circle passes through the oxide layer 13 from the metal film combined substrate 56 and passes through the chalcogenide-based light absorption (light emission) layer 14. Supplied in sufficient quantity.

  Therefore, when the optical element 55 is manufactured, a conventional alkali metal supply method by natural diffusion from the alkali metal-containing layer to the chalcogenide-based light absorption (light emission) layer 14 can be used as it is. Therefore, according to the optical element 55 of this embodiment, a known chalcogenide-based light absorption (light emission) layer forming method (three-stage method, selenization method, etc.) can be used as it is. In addition, since the metal film combined substrate 56 is formed under the oxide layer 13 having the scattering mirror structure, the metal film combined substrate 56 is formed at the boundary portion between the chalcogenide-based light absorbing (emitting) layer 14 and the oxide layer 13. There is no effect of deteriorating conductivity and transparency.

  In the optical element 55, a thin metal layer (electrode) may be formed between the oxide layer 13 and the chalcogenide-based light absorption (light emission) layer 14 to improve ohmic characteristics. In this case, the same effect as described above can be obtained. In addition, when the oxide layer 13 has conductivity, part or all of the electrodes can be replaced with the oxide layer 13 having conductivity.

Next, an embodiment of a method for manufacturing an optical element according to the present invention will be described.
FIG. 7: shows element sectional drawing in each process of one Embodiment of the manufacturing method of the optical element which concerns on this invention. In the present embodiment, first, a metal film 62 is formed on a substrate 61 as shown in FIG. Here, the substrate 61 is an alkali metal-containing substrate (soda lime glass, etc.) itself, or an alkali metal-containing film (alkali metal compound (NaF, KF, etc.), silicate glass thin film, etc.) is formed on the base substrate. This is a substrate having the above structure. The substrate 61 corresponds to the alkali metal-containing layer 11 described above. The metal film 62 is a thin film formed of a metal material such as Mo or W, and corresponds to the above-described metal film 12 or the like. The substrate 61 includes a case of a film made of flexible material such as polyimide foil or metal foil. In addition, when using the metal film combined substrate 56 described above, the metal film 62 is not required to be formed.

  As a method for forming the metal film 62 on the substrate 61, a sputtering method, a mirrortron method disclosed in JP-A-2008-255389, a reactive plasma deposition (RPD) method, a deposition method, an electron beam (EB) There are evaporation methods, ion plating methods, plating methods, laser ablation methods, aqueous solution precipitation methods and the like. In order to increase the transparency of the metal film 62, oxidation, selenization, and sulfidation may be performed on the metal film 62.

Subsequently, as illustrated in FIG. 7B, an oxide layer 63 is formed over the metal film 62. The oxide layer 63 has a single-layer or multi-layer structure such as silicon oxide (SiO ₂ ), titanium oxide (TiO ₂ ), zinc oxide (ZnO), alumina (Al ₂ O ₃ ), tin oxide (SnO ₂ ), Or it is a three-dimensional structure. Examples of the multilayer structure include a metal film / transparent conductive film structure or a structure in which metal particles are embedded in a transparent conductive film. An example of a three-dimensional structure is a texture structure. As a method for forming the oxide layer 63 on the metal film 62, a sputtering method, a mirrortron method, a reactive plasma deposition (RPD) method, a sol-gel method, a chemical vapor deposition method, a vacuum deposition method, and an ion plating method are used. , Laser ablation, and aqueous solution deposition. Note that the oxide layer 63 may partially include a non-oxide film such as a metal.

  Finally, as shown in FIG. 7C, a chalcogenide-based light absorption (light emission) layer 64 is formed on the surface of the oxide layer 63 to complete the manufacture of the optical element. As a method for forming a chalcogenide-based light absorption (light emission) layer, which is a light absorption (light emission) layer that requires the addition of an alkali metal, a multi-source deposition method (such as a three-stage method), a selenization method, a sulfurization method, an atom There are a layer deposition (ALD) method, a wet film forming method, a molecular beam epitaxy method, a vapor phase growth method (CVD, MOCVD method, etc.), a vacuum deposition method, a spin coating method, and a coating method. The manufactured optical element corresponds to the optical element 10 described above.

In the manufacturing method of the optical element of the present embodiment, the metal film 62 having a function as an alkali metal diffusion layer is formed between the substrate 61 and the oxide layer 63, so that the chalcogenide-based light absorption ( Since the conventional alkali metal supply method by natural diffusion can be used as it is as the alkali metal supply method to the (light emission) layer 64, a known chalcogenide-based light absorption (light emission) layer forming method (three-stage method) , Selenization method, etc.) can be used as they are.
In addition, a step of forming a thin metal layer (electrode) for improving ohmic characteristics is sandwiched on the oxide layer 63 formed by the oxide formation step, and then a chalcogenide-based light is formed on the metal layer (electrode). The absorption (light emission) layer 64 may be formed.

Next, Example 1 of the optical element of the present invention and the result of the verification experiment will be described.
FIG. 8A is a cross-sectional view of Example 1 of the optical element according to the present invention, and FIG. 8B is a cross-sectional view of an example of a general transparent conductive film utilizing CIGS solar cell. In FIGS. 8A and 8B, the same reference numerals are given to the same structural portions. Example 1 of the optical element according to the present invention shown in the sectional view of FIG. 8A is a CIGS solar cell 100, and a metal film made of Mo on a soda lime glass (SLG) substrate 101 which is an alkali metal-containing substrate. 102, and further, a transparent conductive film (ZnO: Ga) 103, a back electrode (positive electrode) 104 made of Mo, and chalcopyrite [Cu (In, Ga) Se ₂ (= CIGS)] on the metal film 102. Light absorbing layer (CIGS layer) 105, buffer layer 106 made of cadmium sulfide (CdS), i-ZnO layer (semi-insulating layer) 107, transparent conductive film (ZnO: Al) 108, surface electrode (negative electrode) 109 made of Al Are sequentially stacked.

  The SLG substrate 101 corresponds to the alkali metal-containing layer 11 in the optical element embodiment described above. The metal film 102 corresponds to the metal film 12 having a function as an alkali metal diffusion promoting layer in the embodiment of the optical element described above. The transparent conductive film (ZnO: Ga) 103 corresponds to the oxide layer 13 in the above-described optical element embodiment. Furthermore, the CIGS layer 105 is an example of the chalcogenide light absorption (light emission) layer 14 in the above-described embodiment, and is a light absorption layer made of a chalcopyrite material. Further, although not shown in the embodiment of the optical element shown in FIG. 1 and the like described above, in this embodiment, the electrode 104 for improving the ohmic characteristics is provided between the transparent conductive film (ZnO: Ga) 103 and the CIGS layer 105. Is formed.

  On the SLG substrate 101, a metal film 102 made of Mo, a transparent conductive film (ZnO: Ga) 103, and a back electrode 104 are laminated by high-frequency magnetron sputtering and reactive plasma deposition, respectively. The CIGS layer 105 is deposited on the back electrode 104 by, for example, a three-step method. Since the three-step method itself is known and is not the gist of the present invention, a detailed description thereof is omitted, but the first step of co-evaporating indium (In), gallium (Ga) and selenium (Se), Subsequently, the vapor deposition method includes a second stage in which copper (Cu) and Se are vapor-deposited simultaneously and finally a third stage in which In, Ga and Se are vapor-deposited at the same time. Further, the buffer layer 106, the i-ZnO layer 107, and the transparent conductive film 108 are formed by chemical bath deposition and high-frequency magnetron sputtering, respectively. Further, the surface electrode 109 is formed on the transparent conductive film 108 by a vacuum deposition method.

Here, as an example, the SLG substrate 101 has a thickness of 0.7 mm, the metal film 102 has a thickness of 0.07 μm, and the transparent conductive film (ZnO: Ga) 103 has a thickness of 0.4 to 0.7 μm. The thickness of the back electrode 104 made of Mo is 0.03 μm, and the thickness of the chalcopyrite light absorption layer (CIGS layer) 105 is 1.8 μm. The buffer layer 106 has a thickness of 0.06 μm, the i-ZnO layer 107 has a thickness of 0.07 μm, and the transparent conductive film 108 has a thickness of 0.5 μm. The effective area of each cell was 0.48 cm ² .

  A CIGS solar cell 150 having a cross-sectional structure shown in FIG. 8B is a typical solar cell generally known as a thin film solar cell using chalcopyrite (CIGS) as a light absorption layer and having high conversion efficiency. It is. Compared with the general CIGS solar cell 150 shown in FIG. 8B, the CIGS solar cell 100 of this example includes a metal film 102 that is a Mo film inserted between the SLG substrate 101 and the transparent conductive film 103. It is characterized in that it is a structured. Light enters from above the surface electrode 109.

  Next, a description will be given of the results of verification experiments comparing the degree of diffusion of alkali metal (Na) into the CIGS layer 105 in the CIGS solar cell 100 of this example compared with a general CIGS solar cell 150 and the like.

  9 to 11 show the Na concentration distribution in the CIGS layer by secondary ion mass spectrometry (SIMS). 9 to 11, the horizontal axis indicates the depth (Depth) that increases as it proceeds from the CIGS layer 105 toward the SLG substrate 101, and the vertical axis indicates the Na concentration. CIGS layer 105 is formed in the range of about 0.8 μm to about 2.0 μm in FIGS. 9 to 11. 9 to 11, “GZO” indicates a transparent conductive film (ZnO: Ga) (the same applies to FIGS. 12 and 13 described later).

  The distribution characteristic of the general CIGS solar cell 150 using the transparent conductive film shown in FIG. 8B is shown in FIG. 10, whereas the distribution of the solar cell 100 of the present embodiment shown in FIG. The characteristics are as shown in FIG. In the case of a general CIGS solar cell 150 using a transparent conductive film, as shown in FIG. 10, the Na diffusion layer from the SLG substrate 101 to the CIGS layer 105 is very small, and the diffusion is inhibited by the transparent conductive film 103. Was confirmed.

  On the other hand, in the solar cell 100 of this example, as shown in FIG. 11, the amount of Na diffusion from the SLG substrate 101 to the CIGS layer 105 is large, and the transparent conductive film 103 made of alkali metal (Na) is formed by the metal film 102. It was confirmed that the diffusion of is greatly promoted. The amount of Na diffusion in the CIGS layer in the solar cell 100 of the present example is obtained in the case of a general structure in which a back electrode made of Mo and a CIGS layer are laminated in this order without providing a transparent conductive film on the SLG. 9 is almost the same as the Na concentration distribution characteristic shown in FIG.

  FIG. 12 shows the Na concentration distribution in the CIGS layer evaluated by an electron beam microprobe analyzer (EPMA). In the Na concentration distribution evaluated by the electron microprobe analyzer (EPMA) in FIG. 12 (acceleration voltage 5 kV), SLG like “Mo / GZO / SLG” and “GZO / SLG” shown in FIG. In the structure in which the metal film is not provided between the substrate and the transparent conductive film GZO, Na was not observed in the CIGS layer. On the other hand, as shown in “GZO / Mo / SLG” in FIG. 12 and “Mo / GZO / Mo / SLG” shown in FIG. 8A, Mo is formed between the SLG substrate and the transparent conductive film GZO. In the structure in which the metal film was inserted, it was observed that Na concentration was present in the CIGS layer. As a result, it was confirmed that the diffusion of alkali metal (Na) from the SLG substrate in the transparent conductive film 103 was greatly promoted by the metal film 102. In FIG. 12, the presence of a plurality of black circles indicates that the Na concentration is obtained at each evaluation after multiple evaluations.

9-12, in the solar cell 100 of a present Example, it has shown that the metal film 102 by Mo has the effect | action which promotes the spreading | diffusion in the transparent conductive film 103 of the alkali metal (Na) which the SLG board | substrate 101 contains. It was done. The mechanism of Na diffusion is as follows: (1) Alkali metal (Na) and Mo of the metal film 102 form a compound such as Na ₂ MoO ₄ and smoothly diffuse into the upper CIGS layer in the form of the compound. It is conceivable that (2) the film quality of the upper transparent conductive film 103 is changed and the diffusion in the transparent conductive film 103 is promoted.

Next, the electrical characteristics and efficiency of the solar cell of this example will be described in comparison with the electrical characteristics and efficiency of a general solar cell.
FIG. 13 shows the current-voltage characteristics of the solar cell of this example in comparison with the current-voltage characteristics of a general solar cell. In the current-voltage characteristics of FIG. 13, the horizontal axis represents the voltage of the solar cell during light irradiation, and the vertical axis represents the current density obtained by dividing the current of the solar cell during light irradiation by the effective area. In the case of a general CIGS solar cell 150 using a transparent conductive film that does not have the metal film 102, as shown by a dotted line I in FIG. A decrease in the open-circuit voltage) was confirmed.

  On the other hand, the current-voltage characteristics of a solar cell having a general structure in which the back electrode and the CIGS layer are directly stacked without providing a transparent conductive film on the SLG substrate are sufficient for supplying the alkali metal in the CIGS layer. As shown by a solid line III in FIG. 13, the open circuit voltage is greatly improved as compared with the above characteristic I. In addition, as shown by a broken line II in FIG. 13, the solar cell 100 of this example has characteristics comparable to the current-voltage characteristics III of the solar cell having the above general structure.

  Here, a solar cell (1) having a general structure in which a back electrode and a CIGS layer are directly laminated in this order without providing a transparent conductive film on the above SLG substrate, and the solar cell of the present embodiment using the structure of the present invention. For each of the battery 100 (2) and a solar cell (3) having a general transparent conductive film utilization structure, the conversion efficiency, the open voltage that is the output voltage when the terminal is opened, and the current that is shorted Table 1 summarizes the short-circuit current density obtained by dividing the short-circuit current by the effective area and the curve factor that is a parameter obtained by dividing the product of the open-circuit voltage and the short-circuit current by the product of the maximum voltage Vmax and the maximum current Imax. became.

  As can be seen from Table 1, the characteristics (particularly the conversion efficiency) of the solar cell of this example are almost comparable to the characteristics of a solar cell having a general structure that does not have a transparent conductive film between the SLG substrate and the CIGS layer. As a result, it was confirmed that the characteristics were greatly improved as compared with a solar cell having a general structure using a transparent conductive film.

  Note that in the above embodiments and examples, the oxide layer 13 or the like having a single layer structure, a multilayer structure, or a three-dimensional structure may partially include a non-oxide such as a metal. Moreover, the structural part which consists of the alkali metal containing layer 11 and the metal films 21, 31, 41, 51 in the optical elements 20, 30, 40, 50 of the second to fifth embodiments is used as the metal film of the sixth embodiment. A metal film combined substrate similar to the combined substrate 56 may be replaced.

  The optical element of the present invention can be used for a light receiving element, a light sensor, a light emitting element, etc. in addition to a solar cell using a transparent conductive film that realizes a multifunctional back surface structure and a high light absorption rate (or high light emission rate). it can.

10, 20, 30, 40, 50, 55 Optical element 11 Alkali metal-containing layer 12, 21, 41, 51, 62 Metal film 13, 63 Oxide layer 14, 33, 64 Chalcogenide-based light absorbing layer (or light emitting layer) )
DESCRIPTION OF SYMBOLS 22 Reflector or scattering layer 23 Transparent film 32 Oxide layer having texture structure 42 Oxide layer having scattering mirror structure 52 Light absorption (light emission) layer made of oxide 56 Metal film combined substrate 61 Substrate 100 CIGS sun of Example 1 Battery 101 SLG substrate 102 Metal film made of Mo 103 Transparent conductive film (ZnO: Ga)
104 Back electrode made of Mo 105 Chalcopyrite light absorption layer (CIGS layer)
106 Buffer layer (CdS)
107 i-ZnO layer (semi-insulating layer)
108 Transparent conductive film (ZnO: Al)
109 Surface electrode made of Al 150 Common CIGS solar cell using transparent conductive film

Claims (12)

A light-absorbing layer or a light-emitting layer made of a chalcogenide-based material that requires addition of an alkali metal and a single layer, a multilayer structure, or a three-dimensional oxide layer, and a light-emitting layer are stacked in this order above the substrate that supplies the alkali metal. In the optical element,
An alkali metal from the substrate that supplies the alkali metal by the metal film, wherein a metal film having a function as an alkali metal diffusion promoting layer is inserted between the substrate that supplies the alkali metal and the oxide layer. An optical element having a structure in which diffusion in the oxide layer is promoted and the alkali metal is supplied to the light absorbing layer or the light emitting layer.   2. The optical element according to claim 1, wherein the substrate for supplying the alkali metal is an alkali metal-containing substrate itself or a substrate having a structure in which an alkali metal-containing film is formed on a base substrate.   The substrate for supplying an alkali metal and the metal film constitute a metal film combined substrate having a structure in which a metal substrate itself containing an alkali metal or a metal layer containing an alkali metal is formed on a base substrate. The optical element according to claim 1.   3. The optical element according to claim 1, wherein the metal film is a thin film made of molybdenum or tungsten.   The oxide layer has a multilayer structure including a transparent film formed immediately below the light absorption layer or the light emitting layer, and a reflecting mirror or a scattering layer formed immediately below the transparent film. The optical element as described in any one of Claims 1 thru | or 4.   The optical element according to any one of claims 1 to 4, wherein the oxide layer is a transparent conductive film having a three-dimensional structure having a texture structure.   The optical element according to any one of claims 1 to 4, wherein the oxide layer is a transparent conductive film having a scattering mirror structure in which metal particles are embedded.   8. The optical element according to claim 1, wherein an electrode for improving ohmic characteristics is formed between the oxide layer and the light absorption layer or the light emitting layer. .   9. The optical element according to claim 8, wherein the oxide layer has conductivity, and the electrode has a structure in which a part or all of the electrode is replaced with the conductivity oxide. A film forming step of forming a metal film on a substrate for supplying an alkali metal;
An oxide layer forming step of forming an oxide layer having a single layer, a multilayer structure, or a three-dimensional structure on the metal film formed;
Forming a light-absorbing layer or a light-emitting layer made of a chalcogenide-based material that requires the addition of an alkali metal on the formed oxide layer, and including the substrate and the oxide layer. The metal film formed therebetween functions as an alkali metal diffusion promoting layer that promotes diffusion of alkali metal from the substrate in the oxide layer, and the alkali metal from the substrate passes through the oxide layer to A method for producing an optical element, comprising producing an optical element having a structure for supplying to a light absorbing layer or a light emitting layer.   In the film forming step and the oxide layer forming step, the substrate for supplying the alkali metal having a structure in which a metal substrate containing an alkali metal itself or a metal layer containing an alkali metal is formed on a base substrate, The method of manufacturing an optical element according to claim 1, wherein the oxide layer is formed on a metal film combined substrate having a metal film.   The method of manufacturing an optical element according to claim 10, wherein the metal film is a thin film made of molybdenum or tungsten.

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