This project’s objective is to improve our fundamental understanding of the generation, recombination, and transport of carriers within III-V homo- and heterostructures. The research consists of fabricating and characterizing solar cell “ building blocks” such as junctions and heterojunctions as well as basic measurements of material parameters. A significant effort is also being directed at characterizing loss mechanisms in high-quality, III-V solar cells fabricated in industrial research laboratories throughout the United States. The project’s goal is to use our understanding of the device physics of high-efficiency cell components to maximize cell efficiency. A related goal is the demonstration of new cell structures fabricated by molecular beam epitaxy (MBE). The development of measurement techniques and characterization methodologies is also a project objective. We expect that the insight into HI-V device physics occurring during the course of this work will help to identify paths towards liigher efficiency III-V cells. This report describes our progress during the fourth year of the project. The past year’s efforts centered on completing studies of heavy doping effects in p+-GaAs and assessing the importance of similar effects in n+-GaAs, and at continuing research on characterizing, controlling, and passivating perimeter recombination currents. We also initiated work to identify the dominant loss mechanisms in Alo.2Gao.8As solar cells and brought On-line a new MBE growth facility and demonstrated the high-quality of the films by fabricating, with assistance from Spire Corporation, 23.8% 1-sun solar cells. Our work has benefited greatly from interactions with industrial researchers. We owe special thanks to Steve Tobin, Stan Vemon, and their colleagues at Spire Corporation for providing Alo.2Gao.8As films and cells for our basic studies and for fabricating high-efficiency cells from our MBE-grown films. The work described in this report was supported by the Solar Energy Research Institute. Cecile Lebouef and John Beriner of SERI have provided the long term guidance and encouragement that has made this work possible. Our research also benefited by collaborations with two graduate student researchers not supported by SERI. H.L Chuang was supported by the Indiana Corporation for Science and and Technology and M.E. Klausmeier-Brown by a fellowship from the Eastman Kodak Company.
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