Development of High Efficiency, Stacked Multiple Bandgap Solar Cells.
Final rept. 1 Oct 79-31 Mar 82,
RESEARCH TRIANGLE INST RESEARCH TRIANGLE PARK NC
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This report presents the results of a program conducted at RTI to develop a high efficiency, two junction cascade solar cell suitable for space applications. The bulk of the report focuses on the AlGaAsGaAs material system. This work involved both theoretical and experimental studies. The technology developed for the LPE growth of the planar cascade structure is presented. This includes doping studies, and the development of optimum growth procedures for obtaining high quality LPE layers. Ohmic contact and AR coating technologies are discussed and are related to experimental device performance. Experimental results are presented for individual top cells, bottom cells, and connecting junctions as well as for monolithic cascade structures. The experimental results are correlated with modeling results to determine the factors limiting the performance of these cells. The maximum experimental efficiency achieved during the program was 15.1 under AMO, 1 sun conditions with no AR coating. Material constraints due to the degenerately doped tunnel junction were found to limit cascade cell performance and device yield. In response to the findings on the planar cascade structure, a novel cascade design, the Patterned Tunnel Junction cell, was developed. Author
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