Microcrystalline single-junction and micromorph tandem thin film silicon solar cells

Higher open circuit voltages of the microcrystalline silicon bottom cell have a direct impact on the efficiency of the micromorph (mu c-Si:H/a-Si:H) tandem cell. In this paper it is shown that open circuit voltages over 500 mV can be achieved leading to mu c-Si:H cell efficiencies of 8.5 %. The behaviour of such cells is characterised both by the illuminated and the dark I-V characteristics in function of cell temperature. Microcrystalline cells with V-OC-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 c-Si. Temperature-dependent dark I-V measurements suggest that the dominant recombination mechanism in mu c-Si:H cells is different from that prevailing in a-Si:H solar cells.