Graded Bandgap Solar Cells.
Annual rept. 1 Sep 85-31 Aug 86,
WASHINGTON UNIV RICHLAND JOINT CENTER FOR GRADUATE STUDY
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Graded bandgap solar cells were investigated that have a structure consisting of an N-type graded emitter and a base region with a constant bandgap. The emitter bandgap was 2.1 eV at the front surface and then graded to 1.74 eV at the NP homojunction based on a 1.74 eV bandgap. The Aluminum Gallium Arsenide homojunction had a maximum value for internal photoresponse of 20 while the graded bandgap cell exhibited a peak value of 80. Analyses of photoresponse data indicates the Aluminum Gallium Gallium Arsenide homojunctions are characterized by minority carrier diffusion lengths of only .03 micrometers in the emitter and 0.1 micrometers in the base. Thus, the effective field resulting from the graded emitter in the graded bandgap cell is necessary for an adequate photoresponse. Investigations of heteroface Gallium Arsenide solar cells continued with the purpose of building a data base for processing technology and characterization techniques. GaAs solar cells were fabricated with efficiencies over 17 using a PN homojunction structure ans A1GaAs heteroface. Electro-optical characterization of GaAs cells has resulted in improved understanding of minority carrier properties, surface recombination velocity and current loss mechanisms. Keywords Space power.
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