Investigation of Composite or Stacked Variable Energy Gap Photovoltaic Solar Energy Converter
Final rept. 1 Sep 1959-31 Aug 1960
XEROX ELECTRO-OPTICAL SYSTEMS PASADENA CA
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A theoretical analysis is given of the performance of composite photovoltaic solar energy converters consisting of two separate p-n junction cells of differing energy gaps. For the ideal case the optimum energy gaps are found to be 1.1 eV and 1.65 eV, and the maximum efficiency 32.5 percent. The optimum energy gaps increase with a departure from the ideal, and the maximum efficiency decreases. A correlation is drawn between the efficiency of carrier collection and the effect of diffused layer resistance, and it is found that the optimum junction depth in a solar cell is approximately one-fourth of the minority carrier diffusion length. On the basis of the analysis, Si is chosen for the lower-energy-gap component of the composite cell, and AlSb and CdSe are selected as possible materials for the higher-energy-gap component. The results of measurements in sunlight of the power output of a composite cell in which Si and CdS form the active elements are given.
- Electrooptical and Optoelectronic Devices