A-SI1-XCX-H ALLOYS FOR MULTIJUNCTION SOLAR-CELLS

a-SiC: H alloys are promising candidates for the top junction alloy in triple junction solar cells. In order to understand the limitations to electronic transport in the alloys, we have measured the photoconductivity and optical absorption using photothermal deflection spectroscopy (PDS). Thin film transistors have also been fabricated and studied. Taken together, the material and device measurements provided strong evidence that electron transport in the material is restricted by declining mobility in the alloys above a bandgap of approximately 1.9 eV. P-i-n devices based on the alloys have exhibited open circuit voltages as high as 1.05 V, but the fill factors of the devices decline at these high voltages. The open circuit voltage of the devices scales with the optical bandgap and measurements of Voc versus temperature indicate generation-recombination controls the open circuit voltage. Triple junction devices containing 1.85-eV a-SiC:H and 1.45-eV SiGe:H have shown conversion efficiencies of 10.2 percent. © 1990 IEEE