JP2009231781A - Multijunction silicon thin film photoelectric converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop a technology for producing an interlayer indicative of proper optical characteristics, in order to provide the multijunction silicon photoelectric converter capable of balancing current generated in each silicon thin film photoelectric conversion unit at a higher value and performing conversion with a higher conversion efficiency. <P>SOLUTION: The multijunction silicon thin film photoelectric converter includes an interlayer 4 wherein a transparent oxide layer 4a is located at first, and n layers (n=2 or more, an integral number) of a laminated layer where a carbon layer 4d/a transparent oxide layer 4c are laminated in order are followed. According to the arrangement, each film thickness is optimized, so that wavelength selectiveness and anti-stress nature are improved while series resistance is maintained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a multi-junction silicon-based thin film photoelectric conversion device having an intermediate layer, characterized in that the layer is laminated in the order of transparent oxide layer / carbon layer / transparent oxide layer / carbon layer / transparent oxide layer. It is about.

  In recent years, photoelectric conversion devices that convert light into electricity using photoelectric effects inside semiconductors have attracted attention and are being developed vigorously. Among these photoelectric conversion devices, silicon-based thin film photoelectric conversion devices are at low temperatures. Since it can be formed on a large area glass substrate or stainless steel substrate, cost reduction can be expected. A thin film photoelectric conversion device generally includes a first electrode, a surface of which is sequentially laminated on an insulating substrate, one or more semiconductor thin film photoelectric conversion units, and a second electrode. Here, the photoelectric conversion unit is generally laminated in the order of a p-type layer, an i-type layer, and an n-type layer, and the i-type photoelectric conversion layer that occupies the main part is amorphous when it is amorphous. It is called a photoelectric conversion unit, and a crystal whose i-type layer is crystalline is called a crystalline photoelectric conversion unit. As a method for improving the conversion efficiency of a photoelectric conversion device, a photoelectric conversion device employing a structure called a multi-junction type in which two or more photoelectric conversion units are stacked is known. In this method, a photoelectric conversion unit including a photoelectric conversion layer including a photoelectric conversion layer having a large optical forbidden bandwidth is disposed on a light incident side of the photoelectric conversion device, and a photoelectric conversion layer including a photoelectric conversion layer having a small band gap in order behind the photoelectric conversion layer. By arranging one or more of these, photoelectric conversion over a wide wavelength range of incident light is possible, and conversion efficiency of the entire apparatus is improved by effectively using incident light. In the present application, the photoelectric conversion unit relatively disposed on the light incident side is referred to as a front photoelectric conversion unit, and the photoelectric conversion unit disposed adjacent to the side farther from the light incident side than this is the rear photoelectric conversion. Called a unit. In a photoelectric conversion device in which three or more photoelectric conversion units are stacked, a rear photoelectric conversion unit arranged second or later from the light incident side is a front photoelectric conversion unit, and is adjacent to a side relatively far from the light incident side. Thus, there are a plurality of rear photoelectric conversion units arranged. Incident light can be used effectively by adopting the above multi-junction structure, but the characteristics of the entire multi-junction photoelectric conversion device, especially the short-circuit current density, is the shorter of the short-circuit current densities of the stacked photoelectric conversion units. Limited to current density. Therefore, in order to improve the characteristics of the entire multi-junction photoelectric conversion device, it is necessary to balance the short-circuit current density generated in each photoelectric conversion unit.

  Therefore, in recent years, there has been proposed a stacked photoelectric conversion device having a structure in which both a light transmitting property and a light reflecting property are interposed between a plurality of stacked photoelectric conversion units and a conductive intermediate layer is interposed. In this case, a part of the light reaching the intermediate layer is reflected, the amount of light absorption in the front photoelectric conversion unit located on the light incident side of the intermediate layer is increased, and the current value generated in the front photoelectric conversion unit Can be increased. For example, when an intermediate reflective layer is inserted into a hybrid photoelectric conversion device composed of an amorphous silicon photoelectric conversion unit and a crystalline silicon photoelectric conversion unit, the amorphous silicon photoelectric conversion is performed without increasing the film thickness of the amorphous silicon layer. The current generated by the unit can be increased. Alternatively, the amorphous silicon photoelectric conversion unit due to photodegradation that becomes conspicuous as the thickness of the amorphous silicon layer increases because the thickness of the amorphous silicon layer necessary to obtain the same current value can be reduced. It is possible to suppress the deterioration of characteristics. In such an intermediate layer, it is preferable that the wavelength region of light absorbed by the front photoelectric conversion unit is selectively reflected and the wavelength region of light absorbed by the rear photoelectric conversion unit is selectively transmitted.

  By configuring the intermediate layer with a plurality of thin films having a difference in refractive index, light interference can be generated and transmission or reflectance in a specific wavelength region can be improved. Further, if the thickness of the intermediate layer is increased, higher-order interference waves can be used, and the transmission or reflectance can be changed more steeply with respect to the wavelength. However, if the film thickness is simply increased, light absorption and series resistance derived from the constituent materials increase.

As an example in which a light-transmitting and conductive intermediate layer is inserted, for example, in Patent Document 1, reflection of light by inserting an intermediate layer consisting only of a conductive oxygenated silicon layer between photoelectric conversion units, It discloses that the short circuit current density is increased as compared with the case where the amount of transmission is controlled and the intermediate layer is not inserted. However, the refractive index of the conductive oxygenated silicon layer is about 1.95, and considering that the refractive index of the silicon layer constituting the photoelectric conversion unit is about 3.3, the difference in refractive index is not sufficient, so that satisfactory. Not all reflection characteristics are obtained. Further, Patent Document 2 discloses that a multilayer film in which a plurality of materials are alternately laminated is inserted into an intermediate layer. However, a polycrystalline silicon layer is used as a part of the multilayer film. In this case, the wavelength selectivity is considered to increase due to the refractive index difference in the multilayer film, but the polycrystalline silicon layer has an optically significant film thickness. If inserted, an absorption loss due to the polycrystalline silicon layer occurs.
JP 2005-135987 A JP 2001-308354 A

  As described above, in order to obtain sufficient reflection characteristics as the intermediate layer, it is necessary to increase the refractive index difference from the front photoelectric conversion unit, and for this purpose, it is necessary to reduce the refractive index of the intermediate layer as much as possible. Further, as described above, it is necessary to increase the reflectance in the wavelength region of light absorbed by the front photoelectric conversion unit, and to decrease the reflectance in the wavelength region of light absorbed by the rear photoelectric conversion unit. By configuring the intermediate layer with a plurality of thin films having a difference in refractive index, light interference can be generated and transmission or reflectance in a specific wavelength region can be improved. Further, if the thickness of the intermediate layer is increased, higher-order interference waves can be used, the reflectance can be changed more steeply with respect to the wavelength, and the wavelength selectivity can be improved. However, if the film thickness is simply increased, light absorption and series resistance derived from the constituent materials increase. In addition, as the film thickness increases, the stress generated between the materials also increases, causing film peeling.

  In order to solve the above problems, the present inventors have reached the following invention. The intermediate layer is a layer laminated in the order of transparent oxide layer / carbon layer / transparent oxide layer / carbon layer / transparent oxide layer, while maintaining the series resistance and stress resistance by optimizing each film thickness. The wavelength selectivity is improved.

That is, the present invention
(1) A multi-junction silicon-based thin film photoelectric conversion device including silicon-based thin film photoelectric conversion units connected in series via an intermediate layer, the intermediate layer starting from a transparent oxide layer, and the subsequent layers It is a layer in which n layers are formed by laminating a set of layers laminated in the order of carbon layer / transparent oxide layer (n is an integer of 2 or more), and (2) the carbon layer is The film contains hydrogen, (3) the carbon layer has a refractive index of 1.35 to 1.70 with respect to light having a wavelength of 600 nm, and (4) a transparent oxide constituting the intermediate layer The layer is formed of zinc oxide, (5) the total thickness of the transparent oxide layer is 100 to 1000 mm, and (6) the total thickness of the carbon layer included in the intermediate layer is 300 to or more. Light characterized by being less than 2000 mm It relates converter.

  By laminating the transparent oxide layer / carbon layer / transparent oxide layer / carbon layer / transparent oxide layer in this order, the stress resistance was remarkably improved as compared with the case where the carbon layer was formed as a single layer. This improved productivity. Further, by adjusting the film thickness of the transparent oxide layer and the carbon layer in the intermediate layer, the reflection characteristics can be sharply changed in an arbitrary wavelength region of light. Thereby, only the light of a wavelength required for the front photoelectric conversion unit can be efficiently reflected by the intermediate layer, and the photoelectric conversion current can be increased.

  Due to the above effects, according to the present invention, a high-performance multi-junction silicon-based photoelectric conversion device can be provided.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each drawing of the present application, dimensional relationships such as thickness and length are appropriately changed for clarity and simplification of the drawings, and do not represent actual dimensional relationships. Moreover, in each figure, the same referential mark represents the same part or an equivalent part.

  FIG. 1 shows a cross-sectional view of a multi-junction silicon-based photoelectric conversion device according to an example of an embodiment of the present invention. On the transparent substrate 1, the transparent electrode layer 2, the front photoelectric conversion unit 3, the intermediate layer 4, the rear photoelectric conversion unit 5, and the back electrode layer 6 are arranged in this order. In FIG. 1, the photoelectric conversion unit is a two-junction photoelectric conversion device including a front photoelectric conversion unit and a rear photoelectric conversion unit. In the present invention, three or more photoelectric conversion units are stacked. It can also be applied to a multi-junction silicon-based photoelectric conversion device. For example, in the three-junction silicon-based photoelectric conversion device arranged in the order of the first photoelectric conversion unit, the second photoelectric conversion unit, and the third photoelectric conversion unit from the light incident side, the first photoelectric conversion unit and the second photoelectric conversion unit are Each may be regarded as a front photoelectric conversion unit and a rear photoelectric conversion unit, and an intermediate layer may be provided in the vicinity of the boundary between them. Alternatively, the second photoelectric conversion unit and the third photoelectric conversion unit may be regarded as a front photoelectric conversion unit and a rear photoelectric conversion unit, respectively, and an intermediate layer may be provided in the vicinity of the boundary between them. Of course, a structure in which a silicon composite layer is provided both near the boundary between the first photoelectric conversion unit and the second photoelectric conversion unit and near the boundary between the second photoelectric conversion unit and the third photoelectric conversion unit may be used. Examples of the 3-junction silicon photoelectric conversion device include an amorphous silicon photoelectric conversion unit as the first photoelectric conversion unit, an amorphous silicon germanium or crystalline silicon photoelectric conversion unit as the second photoelectric conversion unit, and a third photoelectric conversion unit. A case where an amorphous silicon germanium or a crystalline silicon-based photoelectric conversion unit is applied to the unit may be mentioned, but the combination is not limited thereto.

A plate-like member or a sheet-like member made of glass, transparent resin or the like is used for the transparent substrate 1 used in a photoelectric conversion device of a type in which light enters from the substrate side. The transparent electrode layer 2 is preferably made of a conductive metal oxide such as SnO ₂ or ZnO, and is preferably formed using a method such as CVD, sputtering, or vapor deposition. The transparent electrode layer 2 desirably has the effect of increasing the scattering of incident light by having fine irregularities on its surface.

As the back electrode layer 6, it is preferable to form at least one metal layer made of at least one material selected from Al, Ag, Au, Cu, Pt and Cr by sputtering or vapor deposition. Between the photoelectric conversion unit and the metal electrode, ITO, may be formed a layer made of SnO 2, conductive oxides such as _ZnO (not shown).

  A plurality of photoelectric conversion units are arranged behind the transparent electrode layer 2 when viewed from the light incident side. In the case of a structure in which two photoelectric conversion units are stacked as shown in FIG. 1, the front photoelectric conversion unit 3 disposed on the light incident side has a relatively wide bandgap material, for example, an amorphous silicon-based material. A conversion unit or the like is used. The rear photoelectric conversion unit 5 arranged on the rear side includes a material having a relatively narrow band gap, for example, a photoelectric conversion unit made of a silicon-based material containing a crystalline material, an amorphous silicon germanium photoelectric conversion unit, or the like. Used.

  Each photoelectric conversion unit is preferably constituted by a pin junction including a p-type layer, an i-type layer that is a substantially intrinsic photoelectric conversion layer, and an n-type layer. Among these, those using amorphous silicon for the i-type layer are called amorphous silicon photoelectric conversion units, and those using crystalline silicon are called crystalline silicon photoelectric conversion units. Note that the amorphous or crystalline silicon-based material is not only a case where only silicon is used as a main element constituting a semiconductor, but also an alloy material including elements such as carbon, oxygen, nitrogen, and germanium. Good. The main constituent material of the conductive layer is not necessarily the same as that of the i-type layer. For example, amorphous silicon carbide can be used for the p-type layer of the amorphous silicon photoelectric conversion unit, and n A silicon layer (also referred to as μc-Si) containing crystal in the mold layer can also be used.

  In the present invention, between the front photoelectric conversion unit and the rear photoelectric conversion unit, the reflectance for light in the wavelength region that can be absorbed by the front photoelectric conversion unit is high, and the reflectance for light in the wavelength region that cannot be absorbed by the front photoelectric conversion unit is low. An intermediate layer 4 having such reflection characteristics is used. The intermediate layer 4 is characterized by using a multilayer film composed of a transparent oxide layer 4a, a carbon layer 4b, a transparent oxide layer 4c, a carbon layer 4d, and a transparent oxide layer 4e, and functions as an intermediate reflective layer. For this purpose, it is necessary to arrange the photoelectric conversion layer in any position between the photoelectric conversion layer in the front photoelectric conversion unit 3 and the photoelectric conversion layer in the rear photoelectric conversion unit 5. In some cases, the intermediate layer 4 can also serve as a part of the conductive layer in the photoelectric conversion unit.

  As the transparent oxide layer of the intermediate layer, tin oxide, zinc oxide, ITO, a conductive oxygenated silicon layer, or the like can be used. In particular, a multilayer intermediate layer formed by laminating a multilayer film formed by repeating the zinc oxide layer 4a, the carbon layer 4b, the zinc oxide layer 4c, the carbon layer 4d, and the zinc oxide layer 4e is preferable. This is because when only the carbon layer is used as the intermediate layer as the low refractive index layer, the ohmic junction with the photoelectric conversion unit is insufficient and a good electrical junction cannot be formed. Therefore, it is necessary to use an intermediate layer in which a zinc oxide layer capable of forming an electrical junction is inserted between the photoelectric conversion unit and the carbon layer. Further, when the film thickness of the carbon layer is increased in order to improve wavelength selectivity, the film becomes very weak against stress, and film peeling occurs during or after film formation. Therefore, stress resistance is remarkably improved and wavelength selectivity is also improved by inserting a zinc oxide layer that has conductivity and transparency, and a refractive index difference from the carbon layer, unlike the carbon layer. Can be improved.

The method for forming the transparent oxide layer needs to be a means for forming a uniform thin film. For example, in addition to PVD methods such as sputtering and vapor deposition and chemical vapor deposition methods such as various CVD methods, a solution containing a raw material for the transparent oxide layer is applied by spin coating, roll coating, spray coating, dipping coating, etc. There is also a method of forming a transparent oxide layer by heat treatment after coating. For example, conductive oxygenated silicon is produced by additionally introducing CO ₂ gas into the chamber under the same conditions as those for producing the n-type μc-Si layer constituting the photoelectric conversion unit by the plasma CVD method. Is possible and process advantageous. Further, if the carbon layer is also formed by plasma CVD, the photoelectric conversion unit and the intermediate layer can be formed by one plasma CVD, so that productivity is improved. The film thickness of these transparent oxide layers is preferably from 10 to 2000 mm. When the thickness of the transparent oxide layer is thin, the conductivity of the transparent oxide layer is extremely low, which becomes an obstacle in series connection with the photoelectric conversion unit. Moreover, when the film thickness of a transparent oxide layer is thick, transparency may worsen and production cost may also become high.

The carbon layer in the intermediate layer is not particularly limited as long as it is mainly composed of components composed of carbon atoms, but for example, diamond-like carbon, graphite-like carbon, or amorphous carbon can be used. . The carbon film can be produced by a generally known technique, such as a plasma CVD method, a vapor deposition method, or a sputtering method. When the carbon layer is formed by plasma CVD, the raw materials can be those usually used, and there are methane and benzene as the carbon source. For example, a good carbon film can be obtained by a method using methane or methane and hydrogen. it can. In order to improve the stability of the carbon layer, fluorine atoms may be introduced, and tetrafluoromethane, trifluoromethane, difluoromethane, fluoromethane, fluorine-substituted benzene, or the like can be used as a carbon source at that time. Methane does not have to be diluted with hydrogen. The plasma power is not particularly limited, but is preferably 0.02 to 1 W / cm ² . The film thickness of the carbon layer is preferably 100 to 1200 mm in view of the properties of the intermediate layer, and more preferably 400 to 900 mm. When the film thickness is thin, the reflection characteristics are degraded. When the film thickness is large, the film becomes weak against stress and the transparency may be deteriorated. Even when the carbon layer is formed by vapor deposition or sputtering, a high quality film can be obtained by adding hydrogen in advance. The carbon layer according to the present invention preferably has a refractive index of 1.25 to 1.80 for light having a wavelength of 600 nm. If the refractive index is higher than this, the difference in refractive index from the transparent oxide layer becomes insignificant and it becomes difficult to obtain wavelength selectivity. On the other hand, a film having a refractive index lower than this and having conductivity further increases the film thickness for providing wavelength selectivity, and the above manufacturing method also lowers the density, so that it can withstand stress. There is a high possibility of disappearing. Furthermore, increasing the film thickness is considered to cause problems with conductivity. The intermediate layer 4 is an inactive layer that does not contribute to photoelectric conversion, and the light absorbed here does not contribute to power generation. Therefore, the intermediate layer 4 should be as transparent as possible. The reason why the value of light with a wavelength of 600 nm is used as an index as the refractive index of the carbon layer is as follows. Spectral sensitivity of the amorphous silicon photoelectric conversion unit is one of the stacked photoelectric conversion devices in a hybrid photoelectric conversion device in which an amorphous silicon photoelectric conversion unit and a crystalline silicon photoelectric conversion unit are stacked in two stages. The fall of the current and the rise of the spectral sensitivity current of the crystalline silicon photoelectric conversion unit intersect at a wavelength near 600 nm. Therefore, a film that reflects light in the vicinity of 600 nm, that is, a film having a small refractive index with respect to 600 nm light, can easily obtain a reflection characteristic that is excellent in selection, and increases the generated current of the front photoelectric conversion unit. It becomes suitable for. The refractive index can be evaluated using, for example, an ellipsometry method.

  The number n of layers in which the carbon layers / transparent oxide layers after the first transparent oxide layer are stacked in this order is preferably 2 or more, particularly preferably 2 to 5. When it is laminated more than this, although the stress resistance is improved, the wavelength selectivity cannot be improved, and conversely, it is derived from light confinement in the transparent oxide layer, which is a high refractive index in the intermediate layer. Then, the loss that seems to be increasing tends to increase remarkably. Further, as a preferable range, when considering wavelength selectivity, stress resistance, and absorption loss, the balance as an intermediate layer incorporated in the photoelectric conversion unit may include 1 to 3 layers.

  In the following, an amorphous silicon photoelectric conversion unit and a crystalline silicon photoelectric conversion unit are stacked as an example of a method for manufacturing a multi-junction silicon-based photoelectric conversion device including a stacked structure corresponding to the above-described embodiment. Further, a multi-junction silicon photoelectric conversion device having a two-stack superstrate structure will be given and will be described in detail while comparing with a comparative example. In the drawings, the same members are denoted by the same reference numerals, and redundant description is omitted. Moreover, this invention is not limited to a following example, unless the meaning is exceeded.

Example 1
A multi-junction silicon solar cell as Example 1 described with reference to FIG. 1 was produced. Glass was used for the transparent substrate 1 and SnO ₂ was used for the transparent electrode layer 2. The film thickness of the transparent electrode layer 2 at this time was 800 nm, the sheet resistance was 10 ohm / □, and the haze ratio was 15 to 20%. On top of this, a boron-doped p-type silicon carbide (SiC) layer having a thickness of 100 mm, a non-doped amorphous silicon photoelectric conversion layer having a thickness of 2000 mm, and a phosphorous-doped n-type μc-Si layer having a thickness of 200 mm are manufactured by plasma CVD. Filmed. Thereby, the amorphous silicon photoelectric conversion unit 3 of the pin junction which is a front photoelectric conversion unit was formed. Further, an intermediate layer 4 was formed on the amorphous silicon photoelectric conversion unit 3. First, a transparent oxide layer 4a made of zinc oxide was formed by sputtering. In the case where 2 wt% Al is added to zinc oxide as a sputtering target, Ar gas is introduced as a sputtering gas, the substrate is heated to 150 ° C., the pressure is set to 0.27 Pa, and then zinc oxide is added by DC sputtering. The film thickness was 150 mm. In addition, when the zinc oxide layer 4a was measured by the spectroscopic ellipsometry method, the refractive index in wavelength 600nm was 2.1. Next, a carbon layer 4b was formed by a CVD method. Using a plasma CVD apparatus, a carbon film having a film thickness of 400 mm was formed using 50 sccm of methane (100 volume% methane) as a raw material with a substrate temperature of 150 ° C. and a discharge power of 0.27 W / cm ² . When the carbon layer 4b was measured by a spectroscopic ellipsometry method, the refractive index at a wavelength of 600 nm was 1.5. Next, a zinc oxide layer having a thickness of 75 mm was formed as a transparent oxide layer 4c by the same method as that for the zinc oxide layer 4a, and a carbon layer 4d was formed by a method similar to that for the carbon layer 4b by a thickness of 400 mm. Finally, a zinc oxide layer of 75 mm was formed as the transparent oxide layer 4e. On the intermediate layer 4, a boron-doped p-type microcrystalline silicon layer having a thickness of 150 mm, a non-doped crystalline silicon photoelectric conversion layer having a thickness of 35000 mm, and a phosphorus-doped n-type microcrystalline silicon layer having a thickness of 200 mm are formed by plasma CVD. Filmed. Thereby, the crystalline silicon photoelectric conversion unit 5 of the pin junction which is a back photoelectric conversion unit was formed. Further, a ZnO film having a thickness of 800 mm and an Ag film having a thickness of 2500 mm were formed as the back electrode layer 6 on the rear photoelectric conversion unit 5 by sputtering. In order to evaluate the amount of light incident on the front photoelectric conversion unit and the rear photoelectric conversion unit by separating a photoelectric conversion unit having a 1 cm square light receiving area from the multi-junction silicon solar cell obtained as described above, spectral sensitivity characteristics are obtained. was measured, 14.3mA / cm ² in the front photoelectric conversion unit was 14.0mA / cm ² in the rear conversion unit. Since it is connected in series, the rate-limiting current is 14.0 mA / cm ² . Table 1 summarizes the spectral sensitivity current and the presence or absence of film peeling after film formation.

（実施例２）
図１を参照して説明される実施例２としての多接合シリコン太陽電池が作製された。ただし、カーボン層の製膜時の放電電力が０．２２Ｗ／ｃｍ２であり、製膜されたカーボン層の６００ｎｍにおける屈折率が１．７であったことが異なる。分光感度特性を測定したところ、前方光電変換ユニットで１４．８ｍＡ／ｃｍ^２、後方変換ユニットで１２．６ｍＡ／ｃｍ^２あった。直列接続なので律速電流は１２．６ｍＡ／ｃｍ^２となる。分光感度電流を纏めたもの及び製膜後の膜剥がれの有無を表１に示す。

(Example 2)
A multi-junction silicon solar cell as Example 2 described with reference to FIG. 1 was produced. However, the difference is that the discharge power at the time of forming the carbon layer was 0.22 W / cm2, and the refractive index at 600 nm of the formed carbon layer was 1.7. Measurement of the spectral sensitivity characteristics, 14.8mA / cm ² in the front photoelectric conversion unit, there 12.6mA / cm ² in the rear conversion unit. Since it is connected in series, the rate-limiting current is 12.6 mA / cm ² . Table 1 summarizes the spectral sensitivity current and the presence or absence of film peeling after film formation.

(Comparative Example 1)
A multi-junction thin-film silicon solar cell having the configuration shown in FIG. After forming the amorphous silicon photoelectric conversion unit 3, a zinc oxide layer was formed as a transparent oxide layer 4a in a thickness of 150 mm in the same manner as in Example 1. Next, the carbon layer 4b was formed into a film of 800 mm in the same manner as in Example 1. When the carbon layer 4b was measured by a spectroscopic ellipsometry method, the refractive index at a wavelength of 600 nm was 1.5. Further, a zinc oxide layer having a thickness of 150 mm was formed thereon as a transparent oxide layer 4c in the same manner as in Example 1. A crystalline silicon photoelectric conversion unit 5 was formed by the same method as in Example 1. Further, a back electrode layer 6 was formed on the crystalline silicon photoelectric conversion unit 5 by the same method as in Example 1. Measurement of the spectral sensitivity characteristics, 14.2mA / cm ² in the front photoelectric conversion unit, there 13.6mA / cm ² in the rear conversion unit. Since it is connected in series, the rate-limiting current is 13.6 mA / cm ² . However, in Comparative Example 1, the film started to peel off in 2 hours after film formation and was completely peeled off in 12 hours. Table 1 summarizes the spectral sensitivity current and the presence or absence of film peeling after film formation.

(Comparative Example 2)
A multi-junction thin-film silicon solar cell having the configuration shown in FIG. In this case, the carbon layer 4b of the intermediate layer 4 was formed by the same method as in Example 2, and the refractive index at 600 nm was 1.7, which is different from Comparative Example 1.
Measurement of the spectral sensitivity characteristics, 14.6mA / cm ² in the front photoelectric conversion unit, there 12.6mA / cm ² in the rear conversion unit. Since it is connected in series, the rate-limiting current is 12.6 mA / cm ² . However, in Comparative Example 1, the film began to peel off 6 hours after the film formation and was completely peeled off in 42 hours. Table 1 summarizes the spectral sensitivity current and the presence or absence of film peeling after film formation.

Cross-sectional view of structure of multi-junction silicon photoelectric conversion device according to the present invention Cross-sectional view of structure of multi-junction silicon photoelectric conversion device in Comparative Examples 1 and 2

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Transparent electrode layer 3 Front photoelectric conversion unit 4 Intermediate layer 4a Transparent oxide layer 4b Carbon layer 4c Transparent oxide layer 4d Carbon layer 4e Transparent oxide layer 5 Back photoelectric conversion unit 6 Back surface electrode layer

Claims (6)

  A multi-junction silicon-based thin film photoelectric conversion device including silicon-based thin film photoelectric conversion units connected in series via an intermediate layer, wherein the intermediate layer starts with a transparent oxide layer, and the subsequent layers are carbon layers / A multi-junction silicon-based thin-film photoelectric conversion device, characterized in that n layers are formed by laminating layers in which transparent oxide layers are sequentially laminated. (N = 2 or greater integer)   The multi-junction silicon-based thin film photoelectric conversion device according to claim 1, wherein the carbon layer contains hydrogen in the film.   3. The multi-junction silicon-based thin film photoelectric conversion device according to claim 1, wherein a refractive index of the carbon layer with respect to light having a wavelength of 600 nm is 1.25 to 1.80.   4. The multi-junction silicon-based thin film photoelectric conversion device according to claim 1, wherein the transparent oxide layer constituting the intermediate layer is formed of zinc oxide.   5. The multi-junction silicon-based thin film photoelectric conversion device according to claim 4, wherein a total film thickness of the transparent oxide layer is 100 to 1000 mm. 6. The multi-junction silicon-based thin film photoelectric conversion device according to claim 4, wherein a total film thickness of the carbon layers included in the intermediate layer is not less than 300 mm and not more than 2000 mm.

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