JP2011060970A - Crystalline silicon solar cell and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the photoelectric conversion efficiency of a crystalline silicon solar cell by increasing light uptake to a photoelectric conversion layer. <P>SOLUTION: The crystalline silicon solar cell is characterized by comprising a one conductivity type single crystal silicon substrate with a thickness of no more than 200 μm, a p-type silicon thin film layer disposed on one surface of the substrate, a virtually intrinsic silicon thin film layer disposed between the substrate and the p-type silicon thin film layer, an n-type silicon thin film layer disposed on the other surface of the substrate, a virtually intrinsic silicon thin film layer disposed between the substrate and the n-type silicon thin film layer, a transparent electrode disposed on the p-type and n-type silicon thin film layers, a collector electrode disposed on the transparent electrode, and a protective layer disposed on the collector electrode wherein the transparent electrode contains a conductive oxide layer, in which hydrogen is being doped in the conductive oxide and its carrier concentration is no less than 2×20<SP>21</SP>cm<SP>-3</SP>, while the resistivity of the transparent electrode is no more than 2×10<SP>-4</SP>Ω cm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a crystalline silicon solar cell having a heterojunction on the surface of a single crystal silicon substrate, and more particularly to a crystalline silicon solar cell excellent in photoelectric conversion efficiency.

  A crystalline silicon solar cell using a crystalline silicon substrate has high photoelectric conversion efficiency, and has already been widely put into practical use as a photovoltaic power generation system. Among these, a crystalline silicon solar cell in which an amorphous silicon thin film having a band gap different from that of single crystal silicon is formed on the surface of the single crystal and a diffusion potential is formed is called a heterojunction solar cell.

  Furthermore, a solar cell in which a thin amorphous silicon layer is interposed between a conductive amorphous silicon thin film for forming a diffusion potential and a crystalline silicon surface is a crystalline silicon solar cell having the highest conversion efficiency. It is known as one of the forms. By forming a thin intrinsic amorphous silicon layer between the crystalline silicon surface and the conductive amorphous silicon-based thin film, the generation of new defect levels due to the film formation is reduced and the crystalline silicon surface is formed. Existing defects (mainly silicon dangling bonds) can be terminated with hydrogen. In addition, it is possible to prevent diffusion of carrier-introduced impurities to the crystalline silicon surface when forming a conductive amorphous silicon-based thin film.

  In recent years, there has been an increasing need to reduce the thickness of a single crystal silicon substrate used from the viewpoint of a raw material problem of a crystalline silicon solar cell. For this reason, a technique for confining light in the substrate is important as the thickness of the substrate is reduced.

  On the other hand, in a heterojunction solar cell using amorphous silicon as a conductive type layer, it is generally necessary to use indium oxide as a transparent electrode on the incident surface and the back surface in terms of transmittance, conductivity, electrical junction and reliability. It is disclosed that it is good from a viewpoint (for example, refer patent document 1). On the other hand, in a thin-film silicon solar cell having a thick i layer, when zinc oxide is used as a conductive oxide layer formed on the back surface n-type layer, the i-type microcrystalline silicon / n-type microcrystalline silicon layer is conductive. Disposing at the interface with the conductive oxide layer is disclosed (for example, see Patent Document 2).

  Patent Document 3 discloses a photovoltaic element in which a diamond-like carbon film having a refractive index in the range of 1.6 to 2.0 is disposed on the back electrode side. However, the carbon layer having a refractive index in this range is amorphous carbon having a dense film.

Patent Document 4 reports indium oxide doped with tungsten as a transparent electrode material. This transparent electrode material has a thickness of 100 nm and a resistivity of 3 to 9 × 10 ⁻⁴ Ω · cm. On the other hand, the transparent electrode material described in Patent Document 5 achieves a resistivity of 2.2 × 10 ⁻⁴ Ω · cm by doping with fluorine. Furthermore, Non-Patent Document 1 achieves a resistivity of 2.1 × 10 ⁻⁴ Ω · cm with indium oxide doped with tin.

  In the crystalline silicon solar cell, the film thickness of the transparent electrode is about 100 nm, but the sheet resistance of the transparent electrode is 20Ω / □ or more. However, in the crystalline silicon solar cell, the collector electrode and the bus bar are provided on the transparent electrode, which is the cause of reducing the effective area for power generation and the conversion efficiency of the module.

  On the other hand, when reducing the area occupied by the collector electrode while using the transparent electrode, it is necessary to increase the conductivity by increasing the thickness of the transparent electrode, which causes a light absorption loss in the transparent electrode. Therefore, the photoelectric conversion efficiency could not be increased.

On page 10 of Non-Patent Document 2, it is described that a carrier concentration of 1.5 × 10 ²¹ cm ⁻³ has been achieved by conductive doping to zinc oxide. However, it is described that obstacles remain for practical use because of its chemical stability. Non-Patent Document 1 describes that the carrier concentration of indium-tin composite oxide (ITO) is 1.3 × 10 ²¹ cm ⁻³ . However, the carrier mobility is as small as 24 cm ² / Vs, and the resistivity is as high as 2.1 × 10 ⁻⁴ Ω · cm.

Japanese Patent No. 4152197 JP 2007-214283 A Japanese Patent No. 3342257 JP 2007-250927 A Japanese Patent No. 3554789

Japan Journal of physics, 46. L685 (2007) Transparent conductive film, Yutaka Sawada, CM Publishing (2005)

  An object of the present invention is to produce a transparent electrode having higher conductivity than before and to improve photoelectric conversion efficiency by increasing the amount of light taken into the photoelectric conversion layer in a crystalline silicon solar cell. .

  As a result of intensive studies in view of the above problems, the present inventors have found that the photoelectric conversion efficiency, particularly the output current, can be improved with the following configuration.

That is, the present invention uses a single-conductivity single crystal silicon substrate having a thickness of 200 μm or less, and has a p-type silicon thin film layer on one surface of the single crystal silicon substrate, and the single crystal silicon substrate and the p-type silicon thin film A substantially authentic silicon-based thin film layer between the layers, an n-type silicon-based thin film layer on the other surface of the single-crystal silicon substrate, and between the single-crystal silicon substrate and the n-type silicon-based thin film layer Crystalline silicon having a substantially genuine silicon-based thin film layer, a transparent electrode on the p-type and n-type silicon thin film layers, a collector electrode on the transparent electrode, and a protective layer thereon In the solar cell, the transparent electrode includes a conductive oxide layer, the conductive oxide is doped with hydrogen, and the carrier concentration is 2 × 20 ²¹ cm ⁻³ or more, And the above transparent It relates to a crystalline silicon solar cell, wherein the electrode resistivity is not more than 2 × 10 ^-4 Ω · cm.

  In a preferred embodiment, the transparent electrode includes a carbon-based thin film having a refractive index of 1.2 to 1.6 at a wavelength of 500 nm, and a conductive oxide layer doped with hydrogen thereon. In addition, the present invention relates to the crystalline silicon solar cell, wherein the conductive oxide layer is embedded in the carbon thin film.

  A preferred embodiment relates to the crystalline silicon-based solar cell, wherein the carbon-based thin film is formed from an aggregate of particulate and / or plate-like carbon materials.

  In a preferred embodiment, the conductive oxide layer is a transparent conductive oxide layer, and the transparent conductive oxide is an oxide of one or more metals selected from zinc, indium, and tin. The present invention relates to the crystalline silicon solar cell.

  The present invention is a method for producing the crystalline silicon solar cell, wherein the conductive oxide layer is formed by a sputtering method, wherein argon and hydrogen are essential as carrier gases during film formation, and oxygen or The present invention relates to a method for producing a crystalline silicon-based solar cell, wherein a film is formed by adding at least one carbon dioxide.

  According to the present invention, it becomes possible to reduce the thickness of the transparent electrode by using a highly conductive transparent electrode, or to reduce the area of the collecting electrode, to reduce light absorption loss by the transparent electrode, or to incorporate light into the photoelectric conversion layer. Therefore, a crystalline silicon solar cell excellent in photoelectric conversion efficiency can be provided.

It is typical sectional drawing which concerns on the crystalline silicon type solar cell of Example 1 of this invention. It is an image by the atomic force microscope (AFM) from the surface of the carbon-type thin film which concerns on this invention. It is an image by the transmission electron microscope (TEM) of the cross section of the carbon-type thin film which concerns on this invention.

The present invention uses a single-conductivity single crystal silicon substrate having a thickness of 200 μm or less, and has a p-type silicon thin film layer on one surface of the single crystal silicon substrate, and the single crystal silicon substrate and the p-type silicon thin film layer Between the single crystal silicon substrate and the n-type silicon thin film layer, and having an n-type silicon thin film layer on the other surface of the single crystal silicon substrate. Crystalline silicon system comprising a substantially authentic silicon-based thin film layer, a transparent electrode on the p-type and n-type silicon-based thin film layers, a collector on the transparent electrode, and a protective layer thereon In the solar cell, the transparent electrode includes a conductive oxide layer, the conductive oxide is doped with hydrogen, and the carrier concentration is 2 × 20 ²¹ cm ⁻³ or more, and The resistance of the transparent electrode It relates crystalline silicon solar cell, wherein the rate is less than 2 × 10 ^-4 Ω · cm.

  First, the one conductivity type single crystal silicon substrate in the crystalline silicon solar cell of the present invention will be described.

  In general, a single crystal silicon substrate contains an impurity that supplies electric charge to silicon in order to provide conductivity. In general, single crystal silicon substrates are classified into an n type in which phosphorus atoms for introducing electrons into Si atoms are supplied and a p type in which boron atoms for introducing holes (also referred to as holes) are supplied. When used in solar cells, electron-hole pairs can be efficiently separated and recovered by providing a strong electric field with the incident-side heterojunction that absorbs the most light incident on the single crystal silicon substrate as the reverse junction. it can. Therefore, the heterojunction on the incident side is preferably a reverse junction. On the other hand, when holes and electrons are compared, the mobility is generally higher for electrons having a smaller effective mass and scattering cross section. From the above viewpoint, the single crystal silicon semiconductor substrate used in the present invention is preferably an n-type single crystal silicon semiconductor substrate.

  As a preferable configuration of the present invention when an n-type single crystal silicon substrate is used, for example, protective layer / collector electrode / transparent electrode layer / p-type amorphous silicon thin film layer / i type amorphous silicon thin film Layer / n-type single crystal silicon substrate / i-type amorphous silicon-based thin film layer / n-type amorphous silicon-based thin film layer / transparent electrode layer / collecting electrode / protective layer. Is preferred.

In the case where the back surface is an n layer, it is more preferable to form a reflective layer on the transparent electrode layer from the viewpoint of light confinement. The reflection layer means a layer that adds a function of reflecting light to the solar cell. For example, a metal layer such as Ag or Al may be used, and white high reflection made of metal oxide fine particles such as MgO, Al ₂ O ₃ , and white zinc. You may form using a material. In addition, by stacking two or more types of dielectric layers with different refractive indexes and film thicknesses, a multilayer film is formed, and the reflected light at the interface in the multilayer film is interfered with, so that light with a certain range of wavelengths can be detected. A photonic structure having reflectivity may be formed. However, when a ceramic material or a dielectric layer is used, since the material is an insulator, it is preferable to form the reflective layer after forming the collector electrode on the conductive oxide.

  Further, when a p-type single crystal silicon substrate is used as the one conductivity type single crystal silicon substrate, a preferred configuration of the present invention is a protective layer / collector electrode / transparent electrode layer / n-type amorphous silicon-based thin film. Layer / i-type amorphous silicon thin film layer / p-type single crystal silicon substrate / i-type amorphous silicon thin film layer / p-type amorphous silicon thin film layer / transparent electrode layer / collecting electrode / protective layer, In this case, it is preferable that the incident surface be an n-layer from the viewpoint of high efficiency recovery of carriers with the reverse junction as the light incident side.

  The incident surface of the single crystal silicon substrate is preferably cut out so as to be a (100) plane. This is because when a single crystal silicon substrate is etched, a texture structure can be easily formed by anisotropic etching with different etching rates of the (100) plane and the (111) plane. In general, the texture size increases as the etching progresses. For example, when the etching time is lengthened, the texture size increases, but the texture size can also be increased by increasing the etchant concentration, the supply rate, and the liquid temperature so as to increase the reaction rate. In addition, since the etching rate varies depending on the surface state where etching is started, the texture size generally differs between the surface on which the process such as rubbing is performed and the surface on which the process is not performed. Also, in the sharp valleys of the texture formed on the substrate surface, defects are likely to occur due to compressive stress when forming a thin film, so the process of relaxing the shape of the texture valleys and peaks formed after texture formation etching It is preferable to perform isotropic etching with low selectivity on the (100) plane and the (111) plane.

As a method for forming a silicon-based thin film on the single crystal silicon substrate thus manufactured, it is particularly preferable to use a plasma CVD method. As the formation conditions of the silicon-based thin film when the plasma CVD method is used, for example, a substrate temperature of 100 to 300 ° C., a pressure of 20 to 2600 Pa, and a high frequency power density of 0.003 to 0.5 W / cm ² are preferably used. As a raw material gas used for forming a silicon-based thin film, a silicon-containing gas such as SiH ₄ or Si ₂ H ₆ or a mixture of these gases and H ₂ is preferably used. As the dopant gas for forming the p-type or n-type layer of the silicon-based thin film in the photoelectric conversion unit, for example, B ₂ H ₆ or PH ₃ is preferably used. Further, since the addition amount of impurities such as P and B may be small, a mixed gas diluted with SiH ₄ or H _{2 in} advance can also be used. Further, by adding a gas containing a different element such as CH ₄ , CO ₂ , NH ₃ , GeH ₄ or the like to the gas, it is possible to alloy and change the energy gap.

  In the crystalline silicon solar cell of the present invention, a p-type silicon thin film layer is provided on one surface of the single crystal silicon substrate, and substantially genuine silicon is provided between the single crystal silicon substrate and the p type silicon thin film layer. A silicon-based thin film layer, and an n-type silicon-based thin film layer on the other surface of the single-crystal silicon substrate, and substantially genuine silicon between the single-crystal silicon substrate and the n-type silicon-based thin film layer. The system thin film layer is provided.

  The substantially authentic i-type silicon thin film layer is preferably i-type hydrogenated amorphous silicon composed of silicon and hydrogen. In this case, when the i-type hydrogenated amorphous silicon layer is formed by CVD, passivation of the single crystal silicon surface can be effectively performed while suppressing impurity diffusion to the single crystal silicon substrate. Further, by changing the amount of hydrogen in the film, it is possible to give an effective profile to the carrier recovery in the energy gap.

  The p-type silicon thin film layer is preferably a p-type hydrogenated amorphous silicon layer or a p-type oxidized amorphous silicon layer. From the viewpoint of impurity diffusion and series resistance, it is preferable to use a p-type hydrogenated amorphous silicon layer for the p-type silicon thin film layer. On the other hand, a p-type oxidized amorphous silicon layer can also be used as a wide gap low refractive index layer from the viewpoint of reducing optical loss.

  The n-type silicon thin film layer is preferably, for example, an n-type hydrogenated amorphous silicon layer, an n-type amorphous silicon nitride layer, or an n-type microcrystalline silicon layer. In the configuration of the present invention, it is particularly preferable to use n-type hydrogenated amorphous silicon that does not contain a crystallization-inhibiting element as the underlying layer of the n-type microcrystalline silicon thin film. Examples of the n-type microcrystalline silicon-based thin film layer include an n-type microcrystalline silicon layer, an n-type microcrystalline silicon carbide layer, and an n-type microcrystalline silicon oxide layer. An n-type microcrystalline silicon layer to which impurities are not actively added is preferable. In the above case, the n-type microcrystalline silicon layer is provided because the crystallinity of the transparent electrode layer formed thereon can be improved as compared with the case where it is formed on the n-type amorphous silicon layer. It is preferable.

  In the present invention, regarding the deposition of the n-side thin film layer, it is preferable to reduce impurity diffusion and deposition damage to the i-type silicon layer. On the other hand, in order to form an n-type microcrystalline silicon layer, it is necessary to generate plasma with high power in order to generate hydrogen plasma with high density. However, the power required for film formation can be reduced by forming a thin film of n-type hydrogenated amorphous silicon in advance and forming an n-type microcrystalline silicon layer using this as a base. Therefore, the n-type silicon thin film layer of the present invention is preferably composed of an n-type hydrogenated amorphous silicon thin film layer and an n-type microcrystalline silicon thin film layer from the i-type silicon thin film layer side.

On the other hand, by adding oxygen or carbon to silicon, the effective optical gap can be widened and the refractive index is lowered, so that optical merit may be obtained. From the above viewpoint, it is preferable to add in a flow ratio range that does not hinder crystallization, for example, CO ₂ / SiH ₄ <10, CH ₄ / SiH ₄ <3.

  The present invention is configured by providing a transparent electrode on the p-type and n-type silicon thin film layers. The transparent electrode is preferably composed of a carbon-based thin film and a conductive oxide. When the transparent electrode has such a configuration, a highly conductive transparent electrode can be produced. Although the reason why the conductivity is improved by this configuration is not clear, it is considered that the conductive oxide supplies the conductive carrier, and the carbon of the carbon-based thin film assists the movement of the conductive carrier. For example, in the case of a crystalline conductive oxide, the scattering of carriers at the grain boundaries causes a decrease in conductivity. However, the presence of a carbon layer at the grain boundaries causes the carriers scattered at the grain boundaries to be carbon. It is considered that it can be taken out to the system thin film side.

  The carbon-based thin film is a layer made of a compound containing carbon as a main component. 2 and 3 are an atomic force microscope (AFM) image (FIG. 2) or a cross-sectional transmission electron microscope (TEM) image (FIG. 3) from the surface of the carbon-based thin film. The carbon-based thin film according to the present invention preferably contains an aggregate of particulate or plate-like carbon-based compounds as shown in FIGS. This means that a structure with a large gap is formed in the layer. Therefore, when the transparent electrode layer is formed, the transparent conductive oxide enters the gap of the carbon-based thin film, and the transparent conductive oxide layer is a single layer. Thus, the conductivity can be improved. The term “penetration” as used herein refers to a state in which a layer in which the carbon-based thin film and the conductive oxide coexist is present in more than half of the film thickness of the carbon-based thin film. It can also be confirmed by performing elemental analysis in the depth direction as in ion mass spectrometry (SIMS) or X-ray photoelectron spectroscopy (XPS).

  Examples of such particulate or plate-like carbon-based compounds include fullerenes, carbon nanotubes, graphene, and carbon nanowalls, but are not limited to these compounds. (Not formed).

  The carbon-based thin film may have a form in which the particulate or plate-like carbon-based compound is present in amorphous carbon.

  The carbon-based thin film may contain hydrogen or oxygen in addition to carbon. This is entered depending on the film forming conditions, and there is no problem in characteristics if both elements are 40 atomic% or less.

  The carbon-based thin film can be produced by general vapor deposition growth. For example, there are a sputtering method, a chemical vapor deposition (CVD) method, a vapor deposition method, and a pulsed laser deposition (PLD) method. Among these, the sputtering method is advantageous in that it is excellent in productivity because it can easily form a large area. In the case of producing a carbon-based thin film by a sputtering method, a film can be formed by using carbon as a target, using argon as a carrier gas, and further adding 2 to 40% by volume of carbon dioxide or oxygen. Furthermore, the refractive index can be controlled by adding hydrogen to the reaction system. As a power source for film formation by sputtering, any power source such as a direct current (DC) power source or a low-frequency / high-frequency power source can be used, and any carbon-based thin film necessary for the present invention can be used. Can be formed.

  The film thickness of the carbon-based thin film is preferably 1 to 50 nm, and more preferably 2 to 30 nm. Since the carbon-based thin film has a porous structure, if the film thickness is too thick, physical strength such as scratch resistance is lowered, which is not preferable.

  Furthermore, since a strong silicon-carbon covalent bond and a strong carbon-oxygen bond are formed in the carbon-based thin film, an effect of improving the adhesion between the semiconductor layer and the conductive oxide layer can be expected.

  The refractive index of the carbon-based thin film according to the present invention is preferably 1.2 to 1.6 at a wavelength of 500 nm. Furthermore, 1.3-1.5 is preferable. The refractive index can be obtained, for example, by fitting from the phase difference and amplitude difference of polarized light measured with a spectroscopic ellipsometer. More specifically, the film thickness and the complex refractive index can be calculated computationally by fitting using the cauchy model. Refractive index and density have a correlation, and those having a low refractive index generally have a low density. When the refractive index is in the above range, the carbon-based thin film has a rough structure, and a conductive oxide enters the carbon-based thin film, so that an improvement in conductivity can be expected. When the refractive index is lower than the above range, the density of the carbon-based thin film is too small, and there is a tendency that there is no effect on improving the conductivity. On the other hand, when the refractive index is too larger than the above range, the density of the carbon-based thin film is increased, the conductive oxide does not enter the carbon-based thin film, and the effect of improving the conductivity tends to be difficult to obtain.

  As the conductive oxide layer, for example, zinc oxide, indium oxide, or tin oxide can be used alone or in combination. Furthermore, a conductive dopant can be added to these. For example, zinc oxide includes aluminum, gallium, boron, silicon, carbon, and the like. Examples of indium oxide include zinc, tin, titanium, tungsten, molybdenum, and silicon. Examples of tin oxide include fluorine. These conductive oxide layers may be used as a single film or may have a laminated structure.

  The conductive oxide in the present invention is characterized by containing hydrogen as a dopant. Although details of the hydrogen-containing state in the conductive oxide layer are unknown, a metal-hydrogen bond state, a metal-hydrogen-oxygen bond state, an oxygen-hydrogen bond state, and the like are conceivable.

The presence or absence of hydrogen in the conductive oxide layer can be specified by X-ray photoelectron spectroscopy, for example, while observing the binding energy of oxygen on the surface, but is most quantified by Rutherford backscattering method. preferable. As an easier method, there is a method of confirming a peak in the region of about 3000 to 3500 cm ⁻¹ by measuring an infrared absorption spectrum. It can also be confirmed by other secondary ion mass spectrometry (SIMS).

  The method for doping hydrogen into the conductive oxide layer can be achieved, for example, by introducing hydrogen into a sputtering carrier gas. Hydrogen may be the lightest atom, and it is difficult to perform sputtering using only hydrogen as a carrier gas. Furthermore, when sputtering is performed only with argon / hydrogen, the amount of oxygen in the conductive oxide layer is remarkably reduced, or metal ions in the conductive oxide are reduced, the film tends to become black, and the conductivity is also deteriorated. There is a tendency and may not function as a transparent electrode. In the present invention, the above problem can be overcome by adding oxygen and / or carbon dioxide to argon / hydrogen, which is essential as a carrier gas in sputtering, preferably.

  For example, the literature (Youn-Seon Kang, Journal of The Electrochemical Society, Vol. 147 (12), 4625 (2000)) describes magnetron sputtering doped with hydrogen. In the case of having an amorphous silicon layer as in this structure, since hydrogen is desorbed from the amorphous silicon layer and a dangling bond is generated, which can be a carrier recombination center. There is a tendency for the function of the solar cell to deteriorate. The manufacturing method according to the present invention is characterized in that hydrogen can be doped even at room temperature to about 150 ° C.

  Furthermore, in the present invention, for example, hydrogen is 2 to 30% by volume, preferably 4 to 10% by volume, and oxygen and / or carbon dioxide is 1 to 30% by volume, preferably 8 to A substrate with a transparent electrode that is excellent in transparency and conductivity can be prepared by containing 15% by volume (note that argon is 40 to 97% by volume, preferably 75 to 88% by volume). According to the present invention, the transparency in the visible light region is improved. This is because the band gap is shifted to the short wavelength side due to the Bernstein-Moss shift that occurs because hydrogen is injected as a conductive carrier. From this, it is considered that the absorption component decreased. From the above gas range, when there is too much hydrogen, the conductive oxide layer tends to be black. Moreover, when there is too much oxygen, electroconductive oxygen deficiency is also filled and there exists a possibility that electroconductivity may fall. When there is too much carbon dioxide, the oxygen deficiency is eliminated as in the case of oxygen, so that the conductivity may be lowered.

  In the present invention, sputtering can be favorably doped with hydrogen by utilizing plasma discharge. A DC power source or a high frequency power source can be used as a power source for causing plasma discharge. Although the pressure in the system at the time of discharge depends on the exhaust speed of the reaction vessel and the exhaust pump, for example, 0.001 Pa to 100 Pa is preferable, and 0.01 Pa to 10 Pa is more preferable. If the pressure is too high or too low, the discharge tends to be unstable. In sputtering, the gas may be continuously introduced or intermittently introduced, but the argon gas that is an inert gas is preferably continuous in order to stabilize the discharge. Hydrogen, oxygen, and carbon dioxide may be continuous or intermittent.

  The film thickness of the conductive oxide layer of the present invention is preferably 10 nm or more and 140 nm or less from the viewpoint of transparency and conductivity. The role of the conductive oxide layer is to transport carriers to the collector electrode, and any film thickness necessary for this purpose may be used. On the other hand, from the viewpoint of transparency, a conductive oxide layer that is too thick may cause a decrease in transmittance due to its own absorption loss, resulting in a decrease in photoelectric conversion efficiency.

The conductive oxide layer of the present invention preferably has a carrier concentration of 2 × 20 ²¹ cm ⁻³ or more and a resistivity of 2 × 10 ⁻⁴ Ω · cm or less, and further has a carrier concentration of 2.5 in ^{× 20 21 cm -3 ~4.5 × 20} 21 cm -3, it is preferable and resistivity of ^{1 × 10 -5 Ω · cm~1.8 ×} 10 -4 Ω · cm. The origin of these conductivities is generally due to free electron drift or diffusion, and substances with such free electrons are reflected by free electrons at wavelengths of 1000 nm and above according to the classic Drude law.・ Absorption occurs. For this reason, when the concentration is higher than the carrier concentration in the above range, free electron reflection and absorption increase, and light may not be sufficiently taken into the photoelectric conversion layer, which may deteriorate the performance. On the other hand, when the carrier concentration is low, it is difficult to obtain sufficient conductivity. For this reason, in order to increase the density of the collector electrode, the opening area is reduced, and the power generation amount may be reduced.

The resistivity of the transparent electrode layer in the present invention is preferably 2 × 10 ⁻⁴ Ω · cm or less, more preferably 1 × 10 ⁻⁵ Ω · cm to 1.8 × 10 ⁻⁴ Ω · cm. More preferred. The origin of these conductivities is generally due to free electron drift or diffusion, and substances with such free electrons are reflected by free electrons at wavelengths of 1000 nm and above according to the classic Drude law.・ Absorption occurs. For this reason, if the resistivity is too low, the transmittance on the long wavelength side may be significantly reduced. On the other hand, if the resistivity is too high, it is necessary to increase the number of collector electrodes or increase the film thickness of the transparent electrode. is there.

  The conductive oxide layer can be formed by a known method. Examples include sputtering, metal organic chemical vapor deposition (MOCVD), thermal CVD, plasma CVD, molecular beam epitaxy (MBE), and pulsed laser deposition (PLD).

  The substrate temperature during the production of the transparent electrode layer is preferably 150 ° C. or lower. When the temperature is higher than that, hydrogen is desorbed from the amorphous silicon layer, dangling bonds are generated in silicon atoms, and there is a tendency that it can become a recombination center of carriers. The low temperature side may be, for example, room temperature, but 50 ° C. or higher is preferable because adhesion at the interface of the silicon semiconductor layer / carbon thin film / conductive oxide layer tends to be improved.

  A collecting electrode may be formed on the transparent electrode layer. The collector electrode can be produced by a known technique such as ink jet, screen printing, conductive wire bonding, spraying, etc., but screen printing is more preferable from the viewpoint of productivity. For the screen printing, a process of forming a collecting electrode by printing a conductive paste composed of metal particles and a resin binder by screen printing is preferably used.

  The cell may be annealed also to solidify the conductive paste used for the collector electrode. By annealing, improvement of the interface characteristics such as improvement of the transmittance / resistivity ratio of the conductive oxide layer and reduction of contact resistance and interface state can be obtained. The annealing temperature is preferably kept in a high temperature region around 100 ° C. from the deposition temperature of the silicon-based thin film. If the annealing temperature is too high, dopant diffusion from the conductive silicon thin film layer to the intrinsic silicon thin film layer, formation of impurity levels due to diffusion of different elements from the conductive oxide layer to the silicon region, amorphous silicon The characteristics may deteriorate due to the formation of defect levels therein.

  By coating a film such as ethylene vinyl acetate (EVA) resin as a protective layer on these layers, physical strength can be improved. Furthermore, it can also serve to prevent deterioration of the silicon layer and electrode layer due to oxygen and moisture. Further, it is possible to suppress loss of optical characteristics by performing blasting or the like having haze on the EVA film. A well-known thing can be used as said protective layer.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to a following example. Spectroscopic ellipsometry is described in J. Org. A. Woollam. Japan VASE was used. The carrier concentration was determined by measuring the Hall effect according to the van der Pauw method. Infrared absorption spectrum was measured using Spectrum 100 manufactured by PerkinElmer.

Example 1
FIG. 1 is a schematic cross-sectional view showing a crystalline silicon solar cell of Example 1 according to the present invention. The crystalline silicon solar cell of this example is a heterojunction solar cell, and has a texture on both sides of the n-type single crystal silicon substrate 1. An i-type amorphous silicon layer 2 / p-type amorphous silicon layer 3 / carbon-based thin film 6 is formed on the incident surface of the n-type single crystal silicon substrate 1. A conductive oxide layer 7 is formed thereon, and a collector electrode 8 is formed thereon. On the other hand, an i-type amorphous silicon layer 4 / n-type amorphous silicon layer 5 / carbon-based thin film 6 is formed on the back surface of the substrate 1. Further, a conductive oxide layer 7 is formed thereon, and a collector electrode 8 is formed thereon.

  The crystalline silicon solar cell of Example 1 shown in FIG. 1 was manufactured as follows.

  An n-type single crystal silicon substrate having an incident plane of (100) and a thickness of 200 μm was washed in acetone, then immersed in a 2 wt% HF aqueous solution for 3 minutes to remove the silicon oxide film on the surface, The rinse with ultrapure water was performed twice. Next, the substrate was dipped in a 5/15 wt% KOH / isopropyl alcohol aqueous solution maintained at 70 ° C. for 15 minutes, and a texture was formed by etching the substrate surface. Thereafter, rinsing with ultrapure water was performed twice. When the surface of the single crystal silicon substrate 1 was observed with an atomic force microscope (manufactured by AFM Pacific Nanotechnology), the substrate surface was most etched and a pyramidal texture with an exposed (111) surface was formed. It had been.

After the etching, the single crystal silicon substrate 1 was introduced into a CVD apparatus, and an i-type amorphous silicon layer 2 was formed to a thickness of 3 nm on the incident surface. The film thickness of the thin film formed in this example was measured by spectroscopic ellipsometry (trade name VASE, manufactured by JA Woollam Co., Ltd.) when the film was formed on a glass substrate under the same conditions. The film forming speed was obtained and calculated on the assumption that the film was formed at the same film forming speed. The film forming conditions for the i-type amorphous silicon layer 2 were a substrate temperature of 150 ° C., a pressure of 120 Pa, a SiH ₄ / H ₂ flow rate ratio of 3/10, and an input power density of 0.011 W / cm ⁻² . A p-type amorphous silicon layer 3 was formed to 4 nm on the i-type amorphous silicon layer 2. The deposition conditions for the p-type amorphous silicon layer 3 were a substrate temperature of 150 ° C., a pressure of 60 Pa, a SiH ₄ / B ₂ H ₆ flow rate ratio of 1/3, and an input power density of 0.01 W / cm ⁻² . . The B ₂ H ₆ gas used above was a gas diluted with H ₂ to a B ₂ H ₆ concentration of 5000 ppm.

Next, 6 nm of i-type amorphous silicon layers 4 were formed on the back side. The film forming conditions for the i-type amorphous silicon layer 4 were a substrate temperature of 150 ° C., a pressure of 120 Pa, a SiH ₄ / H ₂ flow rate ratio of 3/10, and an input power density of 0.011 W / cm ⁻² . An n-type amorphous silicon layer 5 was formed to 4 nm on the i-type amorphous silicon layer 4. The film forming conditions for the n-type amorphous silicon layer 5 were a substrate temperature of 150 ° C., a pressure of 60 Pa, a SiH ₄ / PH ₃ flow rate ratio of 1/2, and an input power density of 0.01 W / cm ⁻² . The PH ₃ gas used above was a gas diluted with H ₂ to a PH ₃ concentration of 5000 ppm.

A carbon-based thin film 6 having a thickness of 10 nm was formed on the p-type amorphous silicon layer 3 and the n-type amorphous silicon layer 5. The film forming conditions were as follows: the substrate temperature was 150 ° C., carbon was used as the target, argon and carbon dioxide were used as the carrier gases, 80 sccm and 20 sccm, respectively, and a power density of 0.5 W / cm ^{2 was} applied at a pressure of 8.0 Pa. To form a film. When the surface of this carbon-based thin film was observed with AFM, it was observed as a collection of particles (FIG. 2). The refractive index of the carbon-based thin film was measured by spectroscopic ellipsometry and found to be 1.4.

A 100 nm thick indium-tin composite oxide (ITO: containing 10% by weight of tin oxide) was formed as a conductive oxide layer 7 thereon. The film forming conditions were as follows: the substrate temperature was set to 150 ° C., indium-tin composite oxide (ITO: containing 10% by weight of tin oxide) was used as a target, and argon, hydrogen, and oxygen were used as carrier gases at 80, 5, and 10 sccm, respectively. The film was formed at a power density of 0.5 W / cm ² at a pressure of 0.2 Pa.

  Finally, a silver paste was screen-printed on the transparent electrode layer to form a comb-shaped electrode, thereby forming a collector electrode 8. The interval between the collector electrodes was 10 mm.

This carbon-based thin film 10 nm and ITO 100 nm were formed on an intrinsic silicon substrate (resistance of 1 × 10 ⁶ Ω / □ or more) under the same conditions as described above. When this carrier concentration was measured, it was 3.0 × 10 ⁻²¹ cm ⁻³ , and when this resistivity was measured, it was 1.8 × 10 ⁻⁴ Ω · cm. Further, in the infrared absorption spectrum measured in the attenuated total reflection method (ATR) mode, a broad peak was detected at 3000 to 3500 cm ⁻¹ , suggesting the presence of oxygen-hydrogen bonds.

(Example 2)
A crystalline silicon solar cell was manufactured in the same manner as in Example 1 except that the carbon-based thin film 6 of Example 1 was formed under the conditions of argon, carbon dioxide, and hydrogen of 75 sccm, 20 sccm, and 5 sccm, respectively. . The refractive index of the carbon-based thin film was measured by spectroscopic ellipsometry and found to be 1.5.

This carbon-based thin film 10 nm and ITO 100 nm were formed on an intrinsic silicon substrate (resistance of 1 × 10 ⁶ Ω / □ or more) under the same conditions. When this carrier concentration was measured, it was 2.5 × 10 ⁻²¹ cm ⁻³ , and when this resistivity was measured, it was 1.9 × 10 ⁻⁴ Ω · cm. Further, in the infrared absorption spectrum measured in the attenuated total reflection method (ATR) mode, a broad peak was detected at 3000 to 3500 cm ⁻¹ , suggesting the presence of oxygen-hydrogen bonds.

(Example 3)
A crystalline silicon solar cell was produced in the same manner as in Example 1 except that indium-zinc composite oxide (IZO: containing 10% by weight of zinc oxide) was used as the conductive oxide layer of Example 1. As an IZO target, an indium-zinc composite oxide (IZO: containing 10% by weight of zinc oxide) was used.

A carbon-based thin film of 10 nm and IZO of 100 nm were formed on an intrinsic silicon substrate (resistance of 1 × 10 ⁶ Ω / □ or more) under the same conditions as described above. When this carrier concentration was measured, it was 2.8 × 10 ⁻²¹ cm ⁻³ , and when this resistivity was measured, it was 1.6 × 10 ⁻⁴ Ω · cm. Further, in the infrared absorption spectrum measured in the attenuated total reflection method (ATR) mode, a broad peak was detected at 3000 to 3500 cm ⁻¹ , suggesting the presence of oxygen-hydrogen bonds.

Example 4
A crystalline silicon solar cell was produced in the same manner as in Example 1 except that the conductive oxide layer of Example 1 was a zinc-gallium composite oxide (GZO: containing 2% by weight of gallium oxide). As a GZO target, a zinc-gallium composite oxide (GZO: containing 2% by weight of gallium oxide) was used.

The carbon-based thin film 10 nm and GZO 100 nm were formed on an intrinsic silicon substrate (resistance of 1 × 10 ⁶ Ω / □ or more) under the same conditions as described above. When this carrier concentration was measured, it was 2.2 × 10 ⁻²¹ cm ⁻³ , and when this resistivity was measured, it was 1.9 × 10 ⁻⁴ Ω · cm. Further, in the infrared absorption spectrum measured in the attenuated total reflection method (ATR) mode, a broad peak was detected at 3000 to 3500 cm ⁻¹ , suggesting the presence of oxygen-hydrogen bonds.

(Comparative Example 1)
A crystalline silicon solar cell was produced in the same manner as in Example 1 except that no carbon thin film was provided. The interval between the collecting electrodes was 5 mm.

An ITO 100 nm film was formed on an intrinsic silicon substrate (resistance of 1 × 10 ⁶ Ω / □ or more) under the same conditions as described above. When this carrier concentration was measured, it was 1.5 × 10 ⁻²¹ cm ⁻³ , and when this resistivity was measured, it was 2.4 × 10 ⁻⁴ Ω · cm. Further, no broad peak was detected at 3000 to 3500 cm ⁻¹ in the infrared absorption spectrum measured in the attenuated total reflection method (ATR) mode.

(Comparative Example 2)
A crystalline silicon solar cell was produced in the same manner as in Comparative Example 1 except that the interval between the collector electrodes was 10 mm.

When this carrier concentration was measured, it was 1.5 × 10 ⁻²¹ cm ⁻³ , and when this resistivity was measured, it was 2.4 × 10 ⁻⁴ Ω · cm. Further, no broad peak was detected at 3000 to 3500 cm ⁻¹ in the infrared absorption spectrum measured in the attenuated total reflection method (ATR) mode.

  Photoelectric conversion characteristics of the solar cells of the above examples and comparative examples were evaluated using a solar simulator. Table 1 shows the short-circuit current, open-circuit voltage, fill factor, and output of the solar cell module.

  From the results of the above examples and comparative examples, the conductivity of the transparent electrode is improved by doping the conductive oxide with hydrogen to improve the carrier concentration of the transparent electrode, and the interval between the collecting electrodes can be increased. As a result, it was found that the amount of light taken in and the accompanying short circuit current can be improved. Since the transparent electrode of the comparative example has high resistivity, it is considered that the performance is inferior due to loss of carrier transport.

1. 1. n-type single crystal silicon substrate 2. i-type amorphous silicon layer 3. p-type amorphous silicon layer 4. i-type amorphous silicon layer n-type amorphous silicon layer 6. Carbon-based thin film 7. Conductive oxide layer 8. Current collector

Claims (5)

A single conductivity type single crystal silicon substrate having a thickness of 200 μm or less is used, a p type silicon thin film layer is provided on one surface of the single crystal silicon substrate, and substantially between the single crystal silicon substrate and the p type silicon thin film layer. A genuine silicon thin film layer, an n-type silicon thin film layer on the other surface of the single crystal silicon substrate, and a substantially genuine film between the single crystal silicon substrate and the n type silicon thin film layer. A crystalline silicon solar cell comprising a transparent silicon thin film layer, a transparent electrode on the p-type and n-type silicon thin film layers, a collecting electrode on the transparent electrode, and a protective layer thereon. And
The transparent electrode includes a conductive oxide layer, the conductive oxide is doped with hydrogen, and the carrier concentration is 2 × 20 ²¹ cm ⁻³ or more,
A crystalline silicon solar cell, wherein the transparent electrode has a resistivity of 2 × 10 ⁻⁴ Ω · cm or less.   The transparent electrode is formed to include a carbon-based thin film having a refractive index of 1.2 to 1.6 at a wavelength of 500 nm, and a conductive oxide layer doped with hydrogen thereon, and The crystalline silicon solar cell according to claim 1, wherein the conductive oxide layer is embedded in the carbon-based thin film.   The crystalline silicon-based solar cell according to claim 2, wherein the carbon-based thin film is formed from an aggregate of particulate and / or plate-like carbon materials.   The conductive oxide layer is a transparent conductive oxide layer, and the transparent conductive oxide is an oxide of one or more metals selected from zinc, indium, and tin. 4. The crystalline silicon solar cell according to any one of 1 to 3.   It is a manufacturing method of the crystalline silicon solar cell of Claim 1, Comprising: The said conductive oxide layer is formed into a film by sputtering method, Argon and hydrogen are essential as carrier gas at the time of film formation, and also oxygen or A method for producing a crystalline silicon solar cell, comprising forming a film by adding at least one carbon dioxide.