JP4664060B2 - Chalcopyrite solar cell - Google Patents

Description

  The present invention relates to a chalcopyrite solar cell having a substrate containing mica.

  A chalcopyrite solar cell is a solar cell that includes a chalcopyrite compound (hereinafter also referred to as CIGS) represented by Cu (InGa) Se as a light absorption layer, and has high energy conversion efficiency and almost no light deterioration due to secular change. It has attracted particular attention because it has various advantages such as non-occurrence, excellent radiation resistance, wide light absorption wavelength region, and large light absorption coefficient, and various studies have been made for mass production.

As shown in FIG. 9, this type of chalcopyrite solar cell 10 is provided by laminating a laminated body 14 on a glass substrate 12. Here, the laminated body 14 has a basic structure of a first electrode 16 made of Mo, a light absorption layer 18 made of CIGS, and a transparent second electrode 20 made of ZnO / Al. Between the layer 18 and the second electrode 20, a buffer layer 22 and a high resistance layer (semi-insulating layer) 24 for reducing the difference in thermal expansion coefficient between the light absorption layer 18 and the second electrode 20 are interposed. It is common to be done. Furthermore, an antireflection layer 26 is provided on the second electrode 20 to prevent light incident on light absorption from being reflected and leaking outside. Each of the buffer layer 22, the high resistance layer 24, the anti-reflection layer 26 is, for example, CdS, ZnO, consisting of MgF _2. ZnO and InS may be selected as the material of the buffer layer 22.

  A part of the first electrode 16 is exposed from the laminated body 14, and the first lead portion 28 is provided in the exposed portion. On the other hand, a part of the second electrode 20 is also exposed from the antireflection layer 26, and the second lead portion 30 is provided in the exposed portion.

  When the chalcopyrite solar cell 10 configured as described above is irradiated with light such as sunlight, a pair of electrons and holes is generated in the light absorption layer 18. Electrons gather at the interface of the second electrode 20 (n-type side) at the junction interface between the light absorption layer 18 made of CIGS, which is a p-type semiconductor, and the second electrode 20, which is an n-type semiconductor. The holes gather at the interface of the light absorption layer 18 (p-type side). When this phenomenon occurs, an electromotive force is generated between the light absorption layer 18 and the second electrode 20. Electric energy generated by the electromotive force is taken out as current from the first lead portion 28 and the second lead portion 30 connected to the first electrode 16 and the second electrode 20, respectively.

  The chalcopyrite solar cell 10 shown in FIG. 9 is usually produced as follows. That is, first, the first electrode 16 made of Mo (molybdenum) is formed on the glass substrate 12 made of soda-lime glass or the like by sputtering film formation.

  Next, the first electrode 16 is divided by irradiating laser light. This operation is called scribing.

After cutting waste generated at the time of division is removed by washing with water, Cu, In, and Ga are deposited on the first electrode 16 by sputtering film formation to provide a precursor (precursor). The precursor and the first electrode 16 are accommodated in a heat treatment furnace and annealed in an H ₂ Se gas atmosphere. During the annealing, selenization of the precursor occurs, and a light absorption layer 18 made of CIGS is formed.

  Next, an n-type buffer layer 22 such as CdS, ZnO, or InS is provided on the light absorption layer 18. The buffer layer 22 is formed by, for example, sputtering film formation, chemical bath deposition (CBD), or the like.

  Further, after the high resistance layer 24 such as ZnO is formed by sputtering film formation or the like, the high resistance layer 24, the buffer layer 22, and the light absorption layer 18 are scribed using a laser beam or a metal needle. That is, the high resistance layer 24, the buffer layer 22, and the light absorption layer 18 are divided.

  Next, after the second electrode 20 made of ZnO / Al is provided by sputtering film formation, the second electrode 20, the high resistance layer 24, the buffer layer 22, and the light absorption layer 18 are scribed using a laser beam or a metal needle. Do.

  Finally, the first lead portion 28 and the second lead portion 30 are provided in the exposed portions of the first electrode 16 and the second electrode 20, respectively. Thereby, the chalcopyrite solar cell 10 is obtained.

  The chalcopyrite solar cell 10 obtained in this way is a cell, and normally, a plurality of cells electrically connected to each other and enlarged to a panel shape are put to practical use.

  As described above, glass is usually selected as the material for the substrate. The reason is that the surface of the film laminated on the substrate can be made relatively smooth because it is easily available and inexpensive, and the surface is smooth, and the sodium in the glass absorbs light. This is because energy conversion efficiency increases as a result of diffusion to the layer.

  However, when a glass substrate is used, the temperature at the time of selenizing the precursor cannot be set high, so that it is difficult to advance the selenization to a composition where the energy efficiency is remarkably increased. In addition, since the substrate is thick, there is a problem that when the chalcopyrite solar cell is manufactured, a delivery device for feeding out the glass substrate is increased in size, and the mass of the manufactured chalcopyrite solar cell is increased. Moreover, since the glass substrate has little flexibility, it is difficult to apply a mass production method called a roll-to-roll process.

As a measure to solve this problem, it is recalled that the material of the substrate is changed to something other than glass. For example, Patent Document 1 proposes a chalcopyrite solar cell using a polymer film as a substrate. In addition, Patent Document 2 lists stainless steel as the material of the substrate of the chalcopyrite fuel cell. Patent Document 3 discloses glass, alumina, mica, polyimide, molybdenum, tungsten, nickel, graphite, and stainless steel. Are listed. Here, in Patent Document 2, it is proposed to provide a protective layer made of SiO ₂ or FeF ₂ in order to avoid the stainless substrate from being attacked by selenium during selenization.

JP-A-5-259494 JP 2001-339081 A JP 2000-58893 A

However, when a polymer film is used as a substrate as described in Patent Document 1, the chalcopyrite solar cell has flexibility, but has a problem that it cannot be heated at the time of selenization. For example, it is not possible to 260 ° C. or higher in the polyimide, it is impossible to perform the selenide to be 500 ° C. or higher using H ₂ Se gas.

  Further, the technique described in Patent Document 2 has an aspect that it is difficult to say that the stainless steel substrate is sufficiently protected by the protective layer. That is, in some cases, the stainless steel substrate may be corroded during selenization, which may cause the first electrode to fall off. In addition, since the protective layer is removed and the conductive stainless steel substrate is exposed, a problem that scribing with a metal needle cannot be performed has become apparent.

  Further, in Patent Document 3, various materials are listed as the material of the substrate. However, all of the chalcopyrite solar cell substrates disclosed in Patent Document 3 are glass substrates. For this reason, it is not clear whether corrosion can be avoided during selenization even when other materials are used. For example, it is recognized that when a laminated body is provided using laminated mica in which mica particles are bonded with a resin as a substrate, the laminated body is easily detached from the laminated mica substrate and the energy conversion efficiency is reduced.

  In addition, when a laminated mica substrate is used, it is also recognized that the elements contained in the mica substrate diffuse as impurities into the light absorption layer, which reduces the energy conversion efficiency of the chalcopyrite solar cell.

  It is also conceived that a diffusion preventing layer is provided between the laminated mica substrate and the laminated body in order to prevent the diffusion of impurities into the light absorption layer. However, in this case, there is a concern that impurities diffuse from the diffusion preventing layer to the light absorption layer. In addition, the laminate cannot be held unless it is a material that can be satisfactorily bonded to both the laminated mica substrate and the laminate.

  Thus, it is difficult to construct a chalcopyrite solar cell using a substrate containing mica.

  The present invention has been made to solve the above-described problems, and can be mass-produced. Moreover, the energy conversion efficiency and the open circuit voltage are large, and the laminate is prevented from falling off the substrate. It is an object to provide a chalcopyrite solar cell that can also be used.

In order to achieve the above object, a chalcopyrite solar cell according to the present invention is formed on a first electrode made of metal held on a substrate containing mica via a binder layer, and on the first electrode. A stack of a light absorption layer made of a p-type semiconductor chalcopyrite compound and an n-type semiconductor second electrode formed on the light absorption layer;
The binder layer is a compound containing at least tantalum (Ta) and nitrogen (N);
And the composition ratio N / Ta of N and Ta in the said compound is larger than 1, It is characterized by the above-mentioned.

  First, since the binder layer is interposed between the mica substrate and the laminate, the binder layer also functions as a diffusion preventing layer, and impurities are prevented from diffusing from the mica substrate to the light absorption layer.

  In the present invention, the binder layer is formed of an N-rich compound in which N is present in excess of Ta. Therefore, the free Ta in the binder layer is prevented from diffusing into the light absorption layer as an impurity. This compound may be tantalum nitride (TaN) or a multi-component compound containing other elements in addition to TaN. The same applies to the following.

  As described above, in the present invention, since impurities are prevented from diffusing from the mica substrate and the binder layer to the light absorption layer, the conversion efficiency of the chalcopyrite solar cell is improved.

The chalcopyrite solar cell according to the present invention includes a first electrode made of a metal held on a substrate containing mica via a binder layer, and a p-type semiconductor chalcopyrite formed on the first electrode. A stack of a light absorption layer made of a compound and a second electrode of an n-type semiconductor formed on the light absorption layer;
The binder layer is a compound containing at least tantalum (Ta) and nitrogen (N);
The compound is amorphous.

  Also in the chalcopyrite solar cell having such a configuration, diffusion of free Ta in the binder layer as an impurity into the light absorption layer is suppressed. Also in this case, since the binder layer functions as a diffusion preventing layer, the diffusion of impurities from the mica substrate and the binder layer to the light absorption layer is avoided, and the conversion efficiency of the chalcopyrite solar cell is improved.

In any case, the smoothing includes SiN or SiO ₂ between the insulating substrate and the binder layer, and the undulation of the upper end surface facing the light absorption layer side is smaller than the undulation of the lower end surface facing the substrate side. It is preferable to provide a layer. Thereby, it is possible to avoid the undulations being transferred to the first electrode and the light absorption layer, and as a result, there is an advantage that the open circuit voltage of the chalcopyrite solar cell is increased.

  Here, mica is rich in flexibility. For this reason, for example, it is possible to form a substrate by winding and sending a laminated mica, which will be described later, and cutting it into a predetermined dimension. In other words, since the laminated mica can be wound in a roll shape, it is easy to employ a roll-to-roll process that is a mass production method. That is, mass production of chalcopyrite solar cells can be achieved.

  Further, since mica is less expensive than soda lime glass, the manufacturing cost of the chalcopyrite solar cell can be reduced. And since it is lightweight, the mass of a chalcopyrite solar cell can also be made small.

Furthermore, since the heat resistance and corrosion resistance of mica are remarkably superior to those of a glass substrate, H, compared to a precursor of Cu, In, and Ga (precursor) deposited on the first electrode to provide a light absorption layer, H Selenization can be performed at about 600 to 700 ° C. using ₂ Se gas. Under such conditions, since the selenization of the precursor can be surely progressed, a chalcopyrite solar cell having a large open circuit voltage can be configured.

  Furthermore, since the binder layer is interposed between the mica substrate and the laminate, the bonding strength between the mica substrate and the laminate is ensured. For this reason, it is avoided that the laminated body falls off from the mica substrate.

  In addition, as a mica board | substrate, the laminated mica baked after mixing powdery mica and resin can be mentioned.

  According to the present invention, since the binder layer is provided with an N-rich compound or an amorphous compound, it is possible to prevent impurities from diffusing from the mica substrate and the binder layer to the light absorption layer. For this reason, since the purity of the light absorption layer is maintained, the conversion efficiency of the chalcopyrite solar cell is improved. Moreover, it can avoid that a laminated body falls out of a mica board | substrate by the binding effect | action of a binder layer.

  In addition, the use of a mica substrate facilitates mass production of chalcopyrite solar cells.

  Preferred embodiments of the chalcopyrite solar cell according to the present invention will be described below in detail with reference to the accompanying drawings. The same components as those shown in FIG. 9 are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 1 is a schematic longitudinal sectional view of a chalcopyrite solar cell 50 according to the present embodiment. The chalcopyrite solar cell 50 includes a substrate 52, a stacked body 14, and a smoothing layer 54 and a binder layer 56 interposed between the substrate 52 and the stacked body 14. Here, the binder layer 56 is made of a compound containing at least Ta and N (hereinafter referred to as a TaN compound).

  In the present embodiment, the substrate 52 is formed of laminated mica. Here, the laminated mica refers to what is baked after the powdered mica and the resin are mixed.

The laminated mica is an insulator having a remarkably large resistance value of 10 ¹² to 10 ¹⁶ Ω, and has a high resistance to acid, alkali, H ₂ Se gas, and the like. Furthermore, it is light and flexible. Moreover, while the heat resistance temperature of glass substrates such as soda lime glass is 500 to 550 ° C., the laminated mica exhibits a relatively high heat resistance temperature of 600 to 800 ° C.

  Here, as shown in an enlarged view in FIG. 2, a concave portion 58 and a convex portion 60 exist on the upper end surface of the substrate 52 made of laminated mica. That is, the upper end surface of the laminated mica substrate 52 is greatly undulated.

  When the first electrode 16 constituting the laminated body 14 is laminated on the undulating mica substrate 52, the undulation is transferred also to the upper end surface of the first electrode 16. When the light absorption layer 18 is provided on the first electrode 16 as described above, the open circuit voltage of the chalcopyrite solar cell 50 as the final product tends to decrease.

  Therefore, in the present embodiment, the smoothing layer 54 having a smaller undulation than the laminated mica substrate 52 is interposed. By providing the smoothing layer 54 having a smaller undulation, the undulation transferred to the upper surfaces of the first electrode 16 and the light absorption layer 18 is reduced. Therefore, it is possible to avoid a decrease in the open circuit voltage of the chalcopyrite solar cell 50.

For example, SiN or SiO ₂ is selected as the material of the smoothing layer 54. In this case, there is an advantage that film formation is easy. In addition, since the smoothing layer 54 is well bonded to both the laminated mica substrate 52 and the binder layer 56, the bonding strength can be ensured.

  The binder layer 56 provided on the smoothing layer 54 is a layer for firmly bonding both the laminated mica substrate 52 and the laminated body 14. Also, it serves as a diffusion preventing layer for preventing further diffusion of impurities diffused from the laminated mica substrate 52. In other words, the presence of the binder layer 56 prevents the impurities contained in the laminated mica substrate 52 from diffusing into the light absorption layer 18.

The binder layer 56 is made of a TaN compound as described above. The binder layer 56 made of a TaN compound is favorably bonded to SiN or SiO ₂ that is the material of the smoothing layer 54, Mo that is the material of the first electrode 16, or the like. Therefore, the laminated body 14 can be held on the laminated mica substrate 52 with good bonding strength through the smoothing layer 54.

  Here, the relationship between the composition ratio of N and Ta in the TaN compound constituting the binder layer 56, that is, the value of N / Ta, and the conversion efficiency η (%) of the chalcopyrite solar cell 50 is shown in FIG. From FIG. 3, it can be seen that the conversion efficiency is significantly greater in the case of the N-rich TaN compound in which N is excessive with respect to Ta as compared with the case of the Ta-rich TaN compound.

  For this reason, in the present embodiment, the binder layer 56 is made of an N-rich TaN compound. Thereby, the conversion efficiency η of the chalcopyrite solar cell 50 is increased.

  The reason why the conversion efficiency η of the chalcopyrite solar cell 50 is increased by constituting the binder layer 56 from the N-rich TaN compound is that there is almost no free Ta in the N-rich TaN compound. It is presumed that this is because diffusion to the light absorption layer 18 is avoided.

  N / Ta may be obtained by, for example, an X-ray photoelectron spectrometer (ESCA). N / Ta can be set by controlling the gas flow rate when the binder layer 56 is provided by sputtering the target, for example.

  The X-ray diffraction measurement profiles of the TaN compounds whose composition ratios are shown in FIG. 3 are shown in FIGS. From these FIG. 4 to FIG. 1 TaN compound is amorphous, the remaining No. 1 2, no. 3 TaN compound is a hexagonal crystalline material coordinated in the (110) direction. From this, it is understood that the TaN compound forming the binder layer 56 may be amorphous.

  The thickness of the binder layer 56 is preferably 0.5 to 1.2 μm. When it is less than 0.5 μm, it becomes difficult to function as a diffusion preventing layer. On the other hand, if it exceeds 1.2 μm, it is not easy to ensure the bonding strength.

The laminated body 14 includes a first electrode 16 made of Mo, a light absorption layer 18 made of CIGS, a buffer layer 22 made of CdS, a high resistance layer 24 made of ZnO, a transparent second electrode 20 made of ZnO / Al, MgF _2. The antireflection layer 26 is formed by laminating in this order from the binder layer 56 side. A part of the first electrode 16 and the second electrode 20 is exposed, and a first lead portion 28 and a second lead portion 30 are provided in each exposed portion.

  As described above, the chalcopyrite solar cell 50 according to the present embodiment configured as described above is highly flexible because the substrate 52 is made of laminated mica. For this reason, since the laminated mica can be wound and sent out in a roll shape, it is easy to employ a roll-to-roll process which is a mass production method. That is, mass production of the chalcopyrite solar cell 50 can be achieved.

  Moreover, since the laminated mica is much cheaper and lighter than soda-lime glass, the manufacturing cost of the chalcopyrite solar cell 50 can be reduced and the mass of the chalcopyrite solar cell 50 can be reduced. You can also.

Further, as described above, the heat resistance and corrosion resistance of the laminated mica are remarkably superior to those of the glass substrate 12. For this reason, the Cu, In, and Ga precursors (precursors) deposited on the first electrode 16 to provide the light absorption layer 18 are selenized at about 600 to 700 ° C. using H ₂ Se gas. Can be applied. Under such conditions, the selenization of the precursor can be surely progressed, so that the chalcopyrite solar cell 50 that is the final product has an extremely large open circuit voltage.

  The reason for this is presumed to be that by performing selenization in a gas phase at 600 to 700 ° C., the light absorption layer 18 in which Ga is dispersed in a substantially uniform state is formed, so that the band gap is expanded. The

  Furthermore, according to the present embodiment, since the binder layer 56 is interposed between the laminated mica substrate 52 and the laminated body 14, the bonding strength between the laminated mica substrate 52 and the laminated body 14 is ensured. For this reason, it is avoided that the laminated body 14 falls out of the laminated mica substrate 52.

  Furthermore, the laminated mica substrate 52 contains impurities such as Al, K, Li, Na, Mg, and F. However, the presence of the binder layer 56 may cause these impurities to diffuse into the light absorption layer 18. Be blocked. For this reason, the chalcopyrite solar cell 50 excellent in energy conversion efficiency can be obtained.

  In addition, in this case, the undulation of the upper end surface of the laminated mica substrate 52 is made as small as possible by the smoothing layer 54, so that the undulation is transferred to the first electrode 16 and the light absorption layer 18. As a result, there is an advantage that the open circuit voltage of the chalcopyrite solar cell 50 is increased.

  In addition, when the TaN compound forming the binder layer 56 is N-rich or amorphous, there is almost no free Ta in the binder layer 56, and therefore Ta may diffuse from the binder layer 56 to the light absorption layer 18. It is suppressed. Thereby, the chalcopyrite solar cell 50 excellent in energy conversion efficiency can be obtained.

  In the present embodiment, the smoothing layer 54 is provided. However, if the upper end surface of the laminated mica substrate 52 is smooth to the extent that the energy conversion efficiency of the chalcopyrite solar cell 50 does not decrease, FIG. 7, the binder layer 56 may be provided directly on the laminated mica substrate 52 without providing the smoothing layer 54. TaN, which is the material of the binder layer 56, can be well bonded to the laminated mica, which is the material of the substrate 52. Therefore, also in this case, the bonding strength between the substrate 52 and the laminate 14 can be ensured. Even in this case, the thickness of the binder layer 56 is preferably 0.5 to 1.2 μm.

Further, since the TaN compound is bonded to the laminated mica substrate 52 with a bonding strength larger than that of SiN or SiO ₂ which is the material of the smoothing layer 54, as shown in FIG. 8, in order to ensure further bonding strength. Further, a binder layer 56 may be further provided between the laminated mica substrate 52 and the smoothing layer 54.

  Furthermore, as can be understood from FIGS. 7 and 8, the laminated body 14 may be provided without providing the buffer layer 22, the high resistance layer 24, and the antireflection layer 26.

  Furthermore, the first electrode 16 may be made of W.

  The TaN compound includes not only multi-component compounds containing elements other than tantalum (Ta) and nitrogen (N), but also TaN.

It is a schematic longitudinal cross-sectional view of the chalcopyrite solar cell which concerns on this Embodiment. It is a principal part enlarged view of the chalcopyrite solar cell of FIG. It is a graph which shows the relationship between the value of N / Ta, the film thickness, specific resistance in the TaN compound which comprises a binder layer, and the conversion efficiency of a chalcopyrite solar cell. It is an X-ray-diffraction pattern of the TaN compound which is N / Ta = 1.18. It is an X-ray diffraction pattern of a TaN compound with N / Ta = 0.96. It is an X-ray-diffraction pattern of the TaN compound which is N / Ta = 0.84. It is a schematic longitudinal cross-sectional view of the chalcopyrite solar cell which concerns on another embodiment. It is a schematic longitudinal cross-sectional view of the chalcopyrite solar cell which concerns on another embodiment. It is a schematic longitudinal cross-sectional view of the chalcopyrite solar cell which concerns on a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 50 ... Chalcopyrite type solar cell 12 ... Glass substrate 14 ... Laminate 16 ... First electrode 18 ... Light absorption layer 20 ... Second electrode 52 ... Integrated mica substrate 54 ... Smoothing layer 56 ... Binder layer

Claims (2)

A first electrode made of metal held on a substrate containing mica via a binder layer, a light absorption layer made of a p-type semiconductor chalcopyrite compound formed on the first electrode, and A stacked body with a second electrode of an n-type semiconductor formed on the top;
The binder layer is an amorphous compound containing at least tantalum (Ta) and nitrogen (N);
A chalcopyrite solar cell, wherein the composition ratio N / Ta of N and Ta in the amorphous compound is greater than 1. In claim 1 Symbol placement of the solar cell, between the substrate and the binder layer, a smoothing layer comprising SiN or SiO ₂ is provided, the smoothing layer, undulations of the upper end surface facing the light-absorbing layer side is the A chalcopyrite solar cell characterized by being smaller than the undulation of the lower end surface facing the substrate side.

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