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Photovoltaic device
PATENTS 100 × 100 mm2 (Bayer) and 103 × 103 mm2 (Eurosolare). In the pairs study, pairs of neighboring wafers of the original ingot were processed into solar cells. One wafer received a GBOF grid, the other the same grid rotated by 90°, with little coverage of grain boundaries. In the triplets study the third wafer of each triplet was equipped with a standard H-pattern of the same shading as the GBOF grid. In the pairs study, the researchers found that under standard conditions there is an 89% chance that the GBOF grid increases power output over cells with an identical – but rotated by 90° – grid, the most probable increase being 2.6%. The triplets study shows that there is an 87% chance that the GBOF grid increases power output over cells with the standard Hpattern, the most probable increase being 2.5%. R. Ebner, M. Radike, V. Schlosser and J. Summhammer: Progress in Photovoltaics: Research & Applications 11(1) 1–13 (January 2003).
Swiss diffusion of green power This collaborative research reviews the status of PV take-up in Switzerland. As in many other European countries, green electricity is an emerging product in Switzerland. Although the market is yet to be liberalized, more than 100 of the 1200 Swiss electric utilities offer their customers some sort of green electricity product. Successful companies – like the municipal utilities of Zürich and Bern – have reached customer response rates of up to 4%, while still maintaining cost-based pricing, i.e. charging their customers price premiums of 400–700% per kWh. While
Patents Thin-film solar cell module Assignee: Sharp, Japan This invention provides a thin-film solar cell module capable of suppressing photodegradation and providing a large output. The heat retention member may have a sealing layer with a thermal insulation layer formed on it; the thermal insulation layer may be formed from a sheet-form silica aerogel. Typical amorphous silicon solar cell modules suffer from early-stage deterioration of conversion efficiency (the Staebler-Wronski effect). This is a problem where an a-Si semiconductor is used for a PV conversion layer in a module for outdoor use. Photodegradation can be reduced by reducing the thickness of the a-Si layer in a stacked solar cell module of tandem or triple structure in which unit cells are stacked in two or three layers.
April 2003
most of the products still mainly rely on PV, some utilities have started to introduce mixed green electricity products also including wind power. The ‘Naturemade’ green electricity labeling scheme has evolved from a process with broad stakeholder involvement, including environmental NGOs, scientific institutions, green electricity providers, renewable energy advocates, government bodies and consumer organizations. This analysis is based on a diffusion theory framework. It identifies and characterizes different phases of (past and future) market development, and stresses the importance of eco-labeling as a tool to facilitate the transition from niche to mass market. It also discusses conclusions that can be drawn from the Swiss case towards market development and labeling on a European level. R. Wüstenhagen, J. Markard and B. Truffer: Energy Policy 31(7) 621–632 (June 2003).
Status of the Chinese PV industry This joint paper from researchers at the Institute of Solar Energy, Xi’an Jiaotong University and the Institute of Solar Energy, Shanghai Jiaotong University reviews the technical and commercial characteristics of today’s PV industry in China. Before 2000, China did not have the ability to make production equipment used for solar cells; equipment had to be imported from developed countries. As a result the technologies and equipment used for PV production were obsolescent. However, in 2000 Shanghai GoFly Green Energy Co Ltd, in collaboration with the Institute of Solar Energy of Shanghai at Jiaotong University, installed a production line for crystalline silicon solar cells.
If a-Si solar cell modules are used at higher temperature to recover photodegradation, the photodegradation is reduced and a high output can be obtained. A method of suppressing the radiation of heat of solar light from the rear face of a-Si solar cell modules is achieved by providing a thermal insulator to the rear face. But this technique has problems, e.g. provision of the thermal insulator to the rear face can raise the highest temperature of the cell at some periods and not others. Also, if the module has a thermal insulator with a frame in its periphery, thermal conduction from the module to the frame increases, acting as a radiator and lowering the periphery’s temperature. Other problems relate to construction materials and their disposal, and sealant effectiveness. This thin-film solar cell module is of the light transmission type. It includes a light-transmissive substrate, a front electrode layer, a rear electrode layer, and a PV conversion layer. The rear electrode, front electrode and PV conversion layers are sequentially laminated on the lighttransmissive substrate. A heat retention member
Some of this equipment, such as the solar cell selector, module simulator, laminator, RTP furnace etc., are designed locally. The laminator has been adapted to efficient mass production with a low maintenance cost and effective lamination area of 1000 × 800 mm2. Shanghai GoFly Green Energy is improving process integration and implementing SPC and data systems, to reduce yield losses in electrical and mechanical performance and cut chemical waste. There are many encouraging signs, and many critical challenges, for both the international and indigenous PV industries in the Chinese energy market. The industrial market is not homogeneous, and there are three broad categories that need to be considered: communications, cathodic protection, and remote power. There is still a large gap between the potential of PV based on available resources and current levels of market development. Factors contributing to commercialization barriers for PV in China include government policy and planning; at national government level there is no systematic and comprehensive policy structure tailored for PV development, and coordination among agencies responsible for PV planning is weak. Other factors include the high cost, and the PV industry is only now making the difficult and expensive jump from niche markets. A sizable contribution to electricity production will be attained, but the prospects of reaching this distant goal are good. H. Yang, H. Wang, H. Yu, J. Xi, R. Cui and G. Chen: Energy Policy 31(8) 703–707 (June 2003).
covers the rear electrode layer, and a sealing layer seals the rear electrode layer. In certain instances, the heat retention member has a light absorbance of 40% or more within a near-IR wavelength range of 1500–2000 nm. Patent number: US 6525264 Publication date: 25 February 2003 Inventors: T. Ouchida, K. Kishimoto and Y. Fujioka
Photovoltaic device Assignee: Sanyo Electric, Japan This invention provides a PV device with an ntype microcrystalline Si layer, an i-type microcrystalline SiGe layer and a p-type microcrystalline Si layer laminated on a substrate and using a thin microcrystalline Si-based semiconductor layer as the photoactive layer. To solve the problem of light-induced degradation, a device using microcrystalline (MC) silicon – which is thin and has high stability to light irradiation – as a photoactive layer has been proposed. However, its light absorption coefficient is less than that for a-Si, and a
Photovoltaics Bulletin
13
PATENTS thickness of 2 µm or more is required for use as a photoactive layer. Therefore, a very high forming speed is required for production. However, such forming speed cannot currently be achieved while maintaining good characteristics. To solve these problems, this invention uses MC SiGe with a greater light absorption coefficient than MC Si, and makes a thinner photoactive layer. However, in order to make the photoactive layer 1 µm thick or less, the light absorption coefficient of the MC-SiGe must be at least three times as great as of the MC-Si. To achieve this, the composition ratio of Ge in the MC SiGe should be 20 at% or more. This new device comprises a supporting substrate, a first electrode on the supporting substrate, a semiconductor layer (including a photoactive layer) on this electrode, and a second electrode on the semiconductor layer. The photoactive layer is a MC-SiGe layer with a Ge composition ratio of 20–40 at%; the signal intensity of the Ge–Ge bond is 30–60% of the signal intensity of an Si–Si bond observed by Raman spectroscopy, and the signal intensity of the Si–Ge bond lies in between. The thickness of the photoactive layer is 1 µm or less. A PV device with this structure using thin MC-SiGe as the photoactive layer can provide good conversion efficiency. Patent number: US 6521883 Publication date: 18 February 2003 Inventor: M. Isomura
Backside covering material for solar cell module Assignee: Bridgestone Corporation, Japan The present invention provides a light and thin backside covering material for a solar cell module which has excellent moisture resistance and durability. It also acts a good insulator without causing a short circuit with an underlying wire nor a leak current. The backside covering material for a solar cell module is a three-layer laminated film, with a moisture resistant film sandwiched between two heat- and weather-resistant films. A deposited layer of inorganic oxide is formed on the base film surface to make the moisture-resistant film. The conventional backside covering material is a laminated film comprising metal foil such as aluminum and galvanized iron as a moisturepreventing layer between two resin film layers. However, a solar cell module using conventional materials sometimes has leak current; projections of underlying parts may penetrate through the resin film to cause a shortcircuit with the metal foil; and the laminated resin film without a metal foil cannot provide sufficient moisture resistance. In the backside covering material described here the inorganic oxide used for the deposited
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Photovoltaics Bulletin
layer of the moisture-resistant film is preferably silicon oxide, preferably SiOx, where x is in the range 1.7–1.9. The thickness of the deposited layer is preferably 100–500 Å, ideally 200–400 Å. Silicon oxide is suitable because of its durability in hot and humid conditions. The base film is required to endure heat and pressure during manufacturing of the solar cell module. The base film can be made of a fluororesin such as PTFE, 4-fluoroethyleneperchloroalkoxy copolymer etc., or resins such as polycarbonate, PMMA or polyamide. The base film may include two or more kinds of resins selected from those resins listed above, and may be a multilayer film. The thickness of the base film is preferably 3–300 µm, ideally 5–200 µm. Patent number: US 6521825 Publication date: 18 February 2003 Inventors: T. Miura, K. Akuzawa and Y. Morimura
Processing approach for formation of thin-film Cu(In,Ga)Se2
Assignee: Midwest Research Institute, USA Semiconductor materials comprised of Group IB and Group IIIA metals and Group VIA elements (metal chalcogenides, or Group IB-IIIA-VIA semiconductor thin films) are important candidate materials for PV applications, since many of these semiconductor materials have optical bandgap values well within the terrestrial solar spectrum. Here, a two-stage method for producing IB-IIIA-VIA thin films on a substrate for semiconductor device applications includes first depositing an amorphous IB-IIIA-VIA precursor onto an unheated substrate. The precursor contains all the Group IB and IIIA constituents of the semiconductor thin film to be produced in the stoichiometric amounts desired for the final product. In the second stage the precursor is subjected to a short thermal treatment at 420–550°C in vacuum or under an inert atmosphere to produce a single-phase, IB-III-VIA film. The precursor also preferably comprises the Group VIA element in the stoichiometric amount desired for the final semiconductor thin film. The IB-IIIA-VIA films may be, for example, Cu(In,Ga)(Se,S)2 mixed-metal chalcogenides. The resulting supported IB-IIIA-VIA film is suitable for use in PV applications. Patent number: US 6518086 Publication date: 11 February 2003 Inventors: M.E. Beck and R. Noufi
Silicon coating composition Assignee: JSR Corporation, Japan This novel coating composition contains a silicon compound soluble in a solvent, which can give elementary silicon imparted with excellent semiconducting properties by heat treatment or irradiation of light.
The coating composition is made up of a silicon compound represented by SinX1n (where X1 is a hydrogen or halogen atom, and n is an integer of 4 or more). Alternatively, a modified silane compound represented by SinX2mYl, where X2 is a hydrogen or halogen atom, Y is a boron or phosphorus atom, n is an integer of 3 or more, l is an integer of 1 or more, and m is an integer of n to 2n+3. This coating composition is used in the production of a device for forming a silicon film or a boron- or phosphorous-doped silicon film on a large-area substrate. Patent number: US 6527847 Publication date: 4 March 2003 Inventor: Y. Matsuki
Hard carbon thin film and method for its formation Assignee: Sanyo Electric, Japan There is a continuing need for a hard carbon or diamond thin film which exhibits improved adherence to an underlying layer such as a substrate. In this patent a hard carbon thin film formed on a substrate has a graded structure in which the ratio of sp2 to sp3 carbon–carbon bonding in the thin film decreases in its thickness direction from the thin film/ substrate interface towards the surface of the thin film. A method of forming the thin film involves varying the film-forming ion species over time to produce the composition gradient or structural gradient in the thickness direction of the thin film. Hard carbon thin films exhibit excellent hardness, resistivity, chemical stability etc., and are expected to find application to functional thin films for electronic devices and semiconductors, including as constituent film layers in solar cells. Occasionally, poor adhesion of the hard carbon thin film to an underlying layer becomes problematic. A prior technique to improve its adhesion to a substrate provides a silicon interlayer between the underlying layer and the hard carbon thin film. However, although such conventional techniques have the potential advantage of imparting increased adhesion, delamination of the hard carbon thin film from the underlying layer can occur under the internal stress of the hard carbon thin film, which increases as the thickness increases. In addition, the interlayer must be formed in a separate step, which results in more complicated fabrication. The fabrication method described in this patent overcomes the disadvantages of the prior methods. Patent number: US 6528115 Publication date: 4 March 2003 Inventors: H. Hirano, Y. Domotooma and K. Kuramoto
April 2003
Swiss diffusion of green power This collaborative research reviews the status of PV take-up in Switzerland. As in many other European countries, green electricity is an emerging product in Switzerland. Although the market is yet to be liberalized, more than 100 of the 1200 Swiss electric utilities offer their customers some sort of green electricity product. Successful companies – like the municipal utilities of Zürich and Bern – have reached customer response rates of up to 4%, while still maintaining cost-based pricing, i.e. charging their customers price premiums of 400–700% per kWh. While
Patents Thin-film solar cell module Assignee: Sharp, Japan This invention provides a thin-film solar cell module capable of suppressing photodegradation and providing a large output. The heat retention member may have a sealing layer with a thermal insulation layer formed on it; the thermal insulation layer may be formed from a sheet-form silica aerogel. Typical amorphous silicon solar cell modules suffer from early-stage deterioration of conversion efficiency (the Staebler-Wronski effect). This is a problem where an a-Si semiconductor is used for a PV conversion layer in a module for outdoor use. Photodegradation can be reduced by reducing the thickness of the a-Si layer in a stacked solar cell module of tandem or triple structure in which unit cells are stacked in two or three layers.
April 2003
most of the products still mainly rely on PV, some utilities have started to introduce mixed green electricity products also including wind power. The ‘Naturemade’ green electricity labeling scheme has evolved from a process with broad stakeholder involvement, including environmental NGOs, scientific institutions, green electricity providers, renewable energy advocates, government bodies and consumer organizations. This analysis is based on a diffusion theory framework. It identifies and characterizes different phases of (past and future) market development, and stresses the importance of eco-labeling as a tool to facilitate the transition from niche to mass market. It also discusses conclusions that can be drawn from the Swiss case towards market development and labeling on a European level. R. Wüstenhagen, J. Markard and B. Truffer: Energy Policy 31(7) 621–632 (June 2003).
Status of the Chinese PV industry This joint paper from researchers at the Institute of Solar Energy, Xi’an Jiaotong University and the Institute of Solar Energy, Shanghai Jiaotong University reviews the technical and commercial characteristics of today’s PV industry in China. Before 2000, China did not have the ability to make production equipment used for solar cells; equipment had to be imported from developed countries. As a result the technologies and equipment used for PV production were obsolescent. However, in 2000 Shanghai GoFly Green Energy Co Ltd, in collaboration with the Institute of Solar Energy of Shanghai at Jiaotong University, installed a production line for crystalline silicon solar cells.
If a-Si solar cell modules are used at higher temperature to recover photodegradation, the photodegradation is reduced and a high output can be obtained. A method of suppressing the radiation of heat of solar light from the rear face of a-Si solar cell modules is achieved by providing a thermal insulator to the rear face. But this technique has problems, e.g. provision of the thermal insulator to the rear face can raise the highest temperature of the cell at some periods and not others. Also, if the module has a thermal insulator with a frame in its periphery, thermal conduction from the module to the frame increases, acting as a radiator and lowering the periphery’s temperature. Other problems relate to construction materials and their disposal, and sealant effectiveness. This thin-film solar cell module is of the light transmission type. It includes a light-transmissive substrate, a front electrode layer, a rear electrode layer, and a PV conversion layer. The rear electrode, front electrode and PV conversion layers are sequentially laminated on the lighttransmissive substrate. A heat retention member
Some of this equipment, such as the solar cell selector, module simulator, laminator, RTP furnace etc., are designed locally. The laminator has been adapted to efficient mass production with a low maintenance cost and effective lamination area of 1000 × 800 mm2. Shanghai GoFly Green Energy is improving process integration and implementing SPC and data systems, to reduce yield losses in electrical and mechanical performance and cut chemical waste. There are many encouraging signs, and many critical challenges, for both the international and indigenous PV industries in the Chinese energy market. The industrial market is not homogeneous, and there are three broad categories that need to be considered: communications, cathodic protection, and remote power. There is still a large gap between the potential of PV based on available resources and current levels of market development. Factors contributing to commercialization barriers for PV in China include government policy and planning; at national government level there is no systematic and comprehensive policy structure tailored for PV development, and coordination among agencies responsible for PV planning is weak. Other factors include the high cost, and the PV industry is only now making the difficult and expensive jump from niche markets. A sizable contribution to electricity production will be attained, but the prospects of reaching this distant goal are good. H. Yang, H. Wang, H. Yu, J. Xi, R. Cui and G. Chen: Energy Policy 31(8) 703–707 (June 2003).
covers the rear electrode layer, and a sealing layer seals the rear electrode layer. In certain instances, the heat retention member has a light absorbance of 40% or more within a near-IR wavelength range of 1500–2000 nm. Patent number: US 6525264 Publication date: 25 February 2003 Inventors: T. Ouchida, K. Kishimoto and Y. Fujioka
Photovoltaic device Assignee: Sanyo Electric, Japan This invention provides a PV device with an ntype microcrystalline Si layer, an i-type microcrystalline SiGe layer and a p-type microcrystalline Si layer laminated on a substrate and using a thin microcrystalline Si-based semiconductor layer as the photoactive layer. To solve the problem of light-induced degradation, a device using microcrystalline (MC) silicon – which is thin and has high stability to light irradiation – as a photoactive layer has been proposed. However, its light absorption coefficient is less than that for a-Si, and a
Photovoltaics Bulletin
13
PATENTS thickness of 2 µm or more is required for use as a photoactive layer. Therefore, a very high forming speed is required for production. However, such forming speed cannot currently be achieved while maintaining good characteristics. To solve these problems, this invention uses MC SiGe with a greater light absorption coefficient than MC Si, and makes a thinner photoactive layer. However, in order to make the photoactive layer 1 µm thick or less, the light absorption coefficient of the MC-SiGe must be at least three times as great as of the MC-Si. To achieve this, the composition ratio of Ge in the MC SiGe should be 20 at% or more. This new device comprises a supporting substrate, a first electrode on the supporting substrate, a semiconductor layer (including a photoactive layer) on this electrode, and a second electrode on the semiconductor layer. The photoactive layer is a MC-SiGe layer with a Ge composition ratio of 20–40 at%; the signal intensity of the Ge–Ge bond is 30–60% of the signal intensity of an Si–Si bond observed by Raman spectroscopy, and the signal intensity of the Si–Ge bond lies in between. The thickness of the photoactive layer is 1 µm or less. A PV device with this structure using thin MC-SiGe as the photoactive layer can provide good conversion efficiency. Patent number: US 6521883 Publication date: 18 February 2003 Inventor: M. Isomura
Backside covering material for solar cell module Assignee: Bridgestone Corporation, Japan The present invention provides a light and thin backside covering material for a solar cell module which has excellent moisture resistance and durability. It also acts a good insulator without causing a short circuit with an underlying wire nor a leak current. The backside covering material for a solar cell module is a three-layer laminated film, with a moisture resistant film sandwiched between two heat- and weather-resistant films. A deposited layer of inorganic oxide is formed on the base film surface to make the moisture-resistant film. The conventional backside covering material is a laminated film comprising metal foil such as aluminum and galvanized iron as a moisturepreventing layer between two resin film layers. However, a solar cell module using conventional materials sometimes has leak current; projections of underlying parts may penetrate through the resin film to cause a shortcircuit with the metal foil; and the laminated resin film without a metal foil cannot provide sufficient moisture resistance. In the backside covering material described here the inorganic oxide used for the deposited
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Photovoltaics Bulletin
layer of the moisture-resistant film is preferably silicon oxide, preferably SiOx, where x is in the range 1.7–1.9. The thickness of the deposited layer is preferably 100–500 Å, ideally 200–400 Å. Silicon oxide is suitable because of its durability in hot and humid conditions. The base film is required to endure heat and pressure during manufacturing of the solar cell module. The base film can be made of a fluororesin such as PTFE, 4-fluoroethyleneperchloroalkoxy copolymer etc., or resins such as polycarbonate, PMMA or polyamide. The base film may include two or more kinds of resins selected from those resins listed above, and may be a multilayer film. The thickness of the base film is preferably 3–300 µm, ideally 5–200 µm. Patent number: US 6521825 Publication date: 18 February 2003 Inventors: T. Miura, K. Akuzawa and Y. Morimura
Processing approach for formation of thin-film Cu(In,Ga)Se2
Assignee: Midwest Research Institute, USA Semiconductor materials comprised of Group IB and Group IIIA metals and Group VIA elements (metal chalcogenides, or Group IB-IIIA-VIA semiconductor thin films) are important candidate materials for PV applications, since many of these semiconductor materials have optical bandgap values well within the terrestrial solar spectrum. Here, a two-stage method for producing IB-IIIA-VIA thin films on a substrate for semiconductor device applications includes first depositing an amorphous IB-IIIA-VIA precursor onto an unheated substrate. The precursor contains all the Group IB and IIIA constituents of the semiconductor thin film to be produced in the stoichiometric amounts desired for the final product. In the second stage the precursor is subjected to a short thermal treatment at 420–550°C in vacuum or under an inert atmosphere to produce a single-phase, IB-III-VIA film. The precursor also preferably comprises the Group VIA element in the stoichiometric amount desired for the final semiconductor thin film. The IB-IIIA-VIA films may be, for example, Cu(In,Ga)(Se,S)2 mixed-metal chalcogenides. The resulting supported IB-IIIA-VIA film is suitable for use in PV applications. Patent number: US 6518086 Publication date: 11 February 2003 Inventors: M.E. Beck and R. Noufi
Silicon coating composition Assignee: JSR Corporation, Japan This novel coating composition contains a silicon compound soluble in a solvent, which can give elementary silicon imparted with excellent semiconducting properties by heat treatment or irradiation of light.
The coating composition is made up of a silicon compound represented by SinX1n (where X1 is a hydrogen or halogen atom, and n is an integer of 4 or more). Alternatively, a modified silane compound represented by SinX2mYl, where X2 is a hydrogen or halogen atom, Y is a boron or phosphorus atom, n is an integer of 3 or more, l is an integer of 1 or more, and m is an integer of n to 2n+3. This coating composition is used in the production of a device for forming a silicon film or a boron- or phosphorous-doped silicon film on a large-area substrate. Patent number: US 6527847 Publication date: 4 March 2003 Inventor: Y. Matsuki
Hard carbon thin film and method for its formation Assignee: Sanyo Electric, Japan There is a continuing need for a hard carbon or diamond thin film which exhibits improved adherence to an underlying layer such as a substrate. In this patent a hard carbon thin film formed on a substrate has a graded structure in which the ratio of sp2 to sp3 carbon–carbon bonding in the thin film decreases in its thickness direction from the thin film/ substrate interface towards the surface of the thin film. A method of forming the thin film involves varying the film-forming ion species over time to produce the composition gradient or structural gradient in the thickness direction of the thin film. Hard carbon thin films exhibit excellent hardness, resistivity, chemical stability etc., and are expected to find application to functional thin films for electronic devices and semiconductors, including as constituent film layers in solar cells. Occasionally, poor adhesion of the hard carbon thin film to an underlying layer becomes problematic. A prior technique to improve its adhesion to a substrate provides a silicon interlayer between the underlying layer and the hard carbon thin film. However, although such conventional techniques have the potential advantage of imparting increased adhesion, delamination of the hard carbon thin film from the underlying layer can occur under the internal stress of the hard carbon thin film, which increases as the thickness increases. In addition, the interlayer must be formed in a separate step, which results in more complicated fabrication. The fabrication method described in this patent overcomes the disadvantages of the prior methods. Patent number: US 6528115 Publication date: 4 March 2003 Inventors: H. Hirano, Y. Domotooma and K. Kuramoto
April 2003