Radiation resistant solar cells for communication satellites

Design of N/P silicon solar cells to operate in the inner Van Allen belt is described. Solar cells have been developed with the N+ diffusion layer thickness in the 0.25-0.5 micron range, resulting in high sensitivity in the 0.4-0.7 micron spectral region, and thus long working life in a radiation environment. Dependence of output power, spectral response, and operating life upon the design features is shown. The cells employ a gridded front contact to minimize series resistive losses in the thin N+ layer, and a silicon monoxide antireflective coating adjusted for optimum response in the blue-green. Performance comparisons show that blue-sensitive N/P cells of 10% initial conversion efficiency deliver greater power after prolonged bombardment than conventional P/N cells of high initial efficiency. High efficiency resulting from preparation of red-sensitive cells with long minority carrier diffusion length is not important for long life in radiation environments, since this response deteriorates rapidly. A random sample of several hundred cells from a production group of several thousand has been evaluated in detail on automatic test equipment, and parameter distributions will be shown.