Novel Amorphous Silicon Solar Cell using a Manufacturing Procedure with a Temporary Superstrate
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ABSTRACT We developed a novel temporary-superstrate concept for SnO 2/p-i-n amorphous silicon solar cells. This concept combines roll-to-roll manufacturability, the utilization of light scattering, the conductive properties of Sn0 2 :F, and the possibility of monolithic series connection. To this purpose, the deposition of high quality textured SnO 2 :F layers on aluminum foil has been developed using APCVD. Layers have been obtained with a transmission of 80 % and a sheet resistance of 12 Q/El. After definition of the entire p-i-n cell structure including the back contact, the cell is laminated with a permanent carrier foil. By removing the aluminum foil, light can enter the cell through the textured TCO layer. A
wide variety of transparent encapsulants can be used to finalize the (flexible or preshaped) product. Preliminary cells made according to this scheme have an efficiency of 6 W. INTRODUCTION The Helianthos project was started in 1997 with the purpose to develop a roll-to-roll production method for amorphous silicon thin film solar cells at a manufacturing cost below 0.50 $/Wp [1,21. The Helianthos consortium is sponsored by the Economy, Ecology and Technology program of the Dutch Government and consists of Utrecht University, the Delft and Eindhoven Universities of Technology, the Netherlands Organisation for Applied Scientific Research, and the multinational corporation Akzo Nobel. In our opinion, a break through for photovoltaics will take place when price competitiveness with grid electricity in western countries is within reach, i.e. photovoltaic systems should be capable of generating electricity at : $ 0.10/kWh (in Europe and Japan grid electricity is more expensive than in the U.S.A.). The development is based on a proprietary manufacturing procedure [31, in which only abundant and relatively cheap source materials are used. Cost calculations showed that the envisaged cost level comes within reach using, e.g., a-Si:H/a-SiGe:l1 tandem cells, if a stabilized efficiency of 7 % is achieved in roll-to-roll production technology over a foil width of 130 cm. 713 Mat. Res. Soc. Symp. Proc. Vol. 557 © 1999 Materials Research Society
NOVEL SOLAR CELL MANUFACTURING PROCEDURE General Background In amorphous and microcrystalline thin film silicon solar cells, light trapping is of crucial importance [4]. In amorphous silicon alloy cells, efficient light management allows the active photovoltaic junction to be thin which enhances stable operation. In thin film microor polycrystalline components, that are more stable by nature, enhanced effective optical absorption is necessary to minimize the film thickness. This reduces the recombination losses and the time required for film deposition. The fabrication of amorphous silicon cells on glass in a superstrate configuration, where light scattering is achieved with a textured SnO 2 :F layer, is a well established procedure (e.g. Solarex, Sanyo). The textured SnO 2 :F is usually made by Atmospheric Pressure
Chemical Vapor Deposition (APCVD). This technology results n
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