MICROCRYSTALLINE AND MICROMORPH THIN-FILM SILICON SOLAR CELLS

This paper deals with 4 separate issues: (1) Open circuit voltage (Voc) of microcrystalline silicon (µc-Si:H): The Voc-value of the single-junction µ c-Si:H bottom cell has a direct i mpact on the e fficiency o f the "micromorph" (µc-Si:H/a-Si:H) tandem cell. It i s s hown h ere that open circuit voltage values of 530 mV can b e achieved for µc-Si:H, leading thereby to single-junction cell efficiencies of 8.5 %. (2) The laser-scribing technique commonly u sed in amorphous s ilicon technology has been successfully applied on thick µ c-Si:H cells. (3) A combination o f the hot-wire a nd VHF-GD deposition techniques allows one to d eposit µc-Si:H films with low subbandgap absorption (as measured by PDS) at remarkably high deposition rates of up to 26 A/s. (4) The behaviour of different solar cells was characterised by the illuminated I-V characteristics in function of cell t emperature. Microcrystalline cells with Voc-values higher than 500 mV and "micromorph" tandems possess in general a lower value of the temperature coefficient of the fill factor and thus of the efficiency, when compared to crystalline silicon. Experimental evidence is provided for this. Keywords: Microcrystalline Si - 1: Tandem Solar Cell - 2: VHF-GD - 3