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Investigation of Integrally Composed Variable Energy Gap Photovoltaic Solar Energy Converter

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Technical summary rept. no. 2, 1 Jan-30 Jun 1960

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A statistical comparison of 27 variable gap solar cells and 14 single gap cells fabricated during this work period indicated that the variable gap cells were superior to the single gap cells in 1 efficiency, 2 open circuit voltage, and 3 short circuit current. The average conversion efficiency and the maximum conversion efficiency in the case of variable gap cells were 4.087. and 6.9, respectively, as compared with 2.43 average efficiency and 4.08 maximum efficiency in the single gap cells. Several studies were carried out in which cells were made and evaluated as single gap cells, then diffused with phosphorus to form variable gap cells. Efficiencies, open circuit voltages, etc., invariably improved, even though the second diffusion resulted in deeper Junction depths. A definite improvement in reverse current dark diode characteristics was noted in the variable gap cells with differences of an order of magnitude in the 5-volt region. Results, to date, have Indicated that the sequence of diffusion giving best results is 1 diffusion of sine followed by 2 diffusion of phosphorus. An etching technique developed in the course of the work allows the determination of optimum Junction depth for each cell. After etching to optimum Junction depth, variable gap cells gave higher efficiencies than single gap cells similarly optimized. It is indicated that the p-n Junction depth is less critical in the case of variable gap cells. A consistent Improvement in achieving purity and single crystal structure of the gallium arsenide crystals has resulted in improved and more reproducible solar cell fabrication.

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  • Electrooptical and Optoelectronic Devices

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