A comparison of fill factor and recombination losses in amorphous silicon solar cells on ZnO and SnO2

Effects of ZnO and SnO2 TCO (Transparent Conductive Oxide) substrate materials on hydrogenated amorphous silicon (a-Si:H) p-i-n solar cell performances and recombination kinetics have been investigated. DC and Frequency-resolved photocurrent measurements in a-Si:H p-i-n solar cells of 6 have been carried out experimentally. In particular, the I-V characteristics in the dark and light, the quantum efficiency spectra, the intensity-, bias voltage- and frequency-dependence of photocurrent were obtained. Fill factor (FF) values were determined from I-V characteristics for both types of substrate cells under various illumination levels. The exponent v in the power-law relationship, I-ph alpha G(v) between generating flux density and phatocurrent were determined at different bias voltages (DC) and modulation frequencies. High values of V-alpha (open-circuit voltage), FF, and DC exponent v for the a-Si:H p-i-n solar cell with SnO2 were obtained, but the integrated QE (quantum efficiency), the modulated exponent v were found to be low compared to cells prepared on ZnO substrates. Our results show that these parameters are sensitive to the ZnO and SnO2 Substrate materials which act as a window layer allowing most of the incident light to pass into the i-layer of p-i-n cells. (c) 2008 Elsevier Ltd. All rights reserved.