Research on High-Bandgap Materials and Amorphous Silicon-Based Solar Cells: Final Technical Report, 15 May 1994 - 15 January 1998

This report describes work performed by Syracuse University under this subcontract. Researchers developed a technique based on electroabsorption measurements for obtaining quantitative estimates of the built-in potential Vbi in a-Si:H-based heterostructure solar cells incorporating microcrystalline or a-SiC:H p layers. Using this new electroabsorption technique, researchers confirmed previousestimates of Vbi approx. equal to1.0 V in a-Si:H solar cells with 'conventional' intrinsic layers and either microcrystalline or a-SiC:H p layers. Researchers also explored the recent claim that light-soaking of a-Si:H substantially changes the polarized electroabsorption associated with interband optical transitions (and hence, not defect transitions). Researchers confirmed measurements ofimproved (5X) hole drift mobilities in some specially prepared a-Si:H samples. Disturbingly, solar cells made with such materials did not show improved efficiencies. Researchers significantly clarified the relationship of ambipolar diffusion-length measurements to hole drift mobilities in a-Si:H, and have shown that the photocapacitance measurements can be interpreted in terms of hole driftmobilities in amorphous silicon. They also completed a survey of thin BP:H and BPC:H films prepared by plasma deposition using phosphine, diborane, trimethylboron, and hydrogen as precursor gases.