Ultralight Amorphous Silicon Alloy Photovoltaic Modules For Space Applications
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Ultralight Amorphous Silicon Alloy Photovoltaic Modules For Space Applications Kevin Beernink, Ginger Pietka, Jeff Noch1, Kais Younan, David Wolf, Arindam Banerjee, Jeffrey Yang, Scott Jones1, and Subhendu Guha United Solar Systems Corp., 1100 W. Maple Rd., Troy, MI 48084, U.S.A. 1 Energy Conversion Devices, Inc., 2956 Waterview Drive, Rochester Hills, Michigan 48309, U.S.A. ABSTRACT Results for solar cells with high specific power (W/kg) using amorphous silicon alloy technology are reported. Currently available roll-to-roll production technology capable of high volume has been used to form cells on thinned stainless steel with high specific power. Results of cells on thinned stainless steel formed in batch mode in research and development (R&D) machines are also presented. Cells on polyimide in the early R&D stage have also been formed and are described. An analysis of cell component material and dimension changes to increase specific power shows that specific power ~2000 W/kg is possible as a long-term goal. Cells with specific power ranging from 300 to 400 W/kg for production cells with 8.5 % beginning of life AM0 efficiency to over 1200 W/kg for R&D cells on polyimide substrates are presented. INTRODUCTION The availability of low-cost, lightweight and reliable photovoltaic modules is an important component in reducing the cost of satellites and spacecraft. In terms of the harsh space environment, amorphous silicon (a-Si) alloy cells have several advantages over other material technologies [1]. The deposition process is relatively simple, inexpensive, and applicable for lightweight, flexible substrates. The temperature coefficient has been found to be between –0.2 and –0.3 %/ºC for high efficiency triple-junction a-Si alloy cells, which is superior to crystalline Si devices for high temperature operations. Additionally, the a-Si alloy cells are relatively insensitive to electron and proton bombardment. In particular, modules incorporating United Solar’s a-Si alloy cells have been tested on the MIR space station for 19 months with only minimal degradation [2]. Here we report on a-Si alloy solar cells in various stages of development with high specific power (W/kg) for space applications. Currently available roll-to-roll production technology is used to form cells on a stainless steel substrate. The substrate is thinned from a 5 mil initial thickness to a 1 mil final thickness to reduce the mass of the cells. In an effort to improve the specific power through higher efficiency, cells have been formed in batch mode in R&D machines, with the eventual goal of transferring these results to the production environment. A longer-term effort to develop cells on ultralight polyimide substrates is also underway, and cells have been formed in the R&D mode with very high specific power. In each case, the cells are optimized for the AM0 spectrum. An analysis of changes in cell component material and dimensions to increase specific power shows that it is possible, through a combination of efficiency improvement and mass
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