a-Si/sub 1-x/C/sub x/: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 on electronic transport in the alloys, the photoconductivity and optical absorption were measured using photothermal deflection spectroscopy (PDS). Thin-film transistors have also been fabricated and studied. Taken together, the material and device measurements provide 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 optical bandgap, and measurements of V/sub oc/ versus temperature indicate that 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%.<
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