A comparative study of photoconductivity and carrier transport in a-Si:H p–i–n solar cells with different back contacts

Effects of different back contacts (Al, Cr, ZnO/Ag, Ag) have been measured on hydrogenated amorphous silicon (a-Si:H) p–i–n solar cell performances and are interpreted in terms of changing recombination kinetics. Dc and frequency-resolved photocurrent measurements in a-Si:H p–i–n solar cells have been carried out experimentally. In particular, the J–V characteristics in the dark and light, the external quantum efficiency spectra, the intensity-, temperature-, bias voltage- and frequency-dependence of photocurrent were obtained. Fill factor (FF) values were determined from J–V characteristics for p–i–n cells with different back contacts under various illumination levels. The exponent ν   in the power-law relationship, Iph∝GυIph∝Gυ, between generating flux density and photocurrent were determined at different bias voltages (dc) and modulation frequencies. The activation energies were obtained from the temperature-dependence of photocurrent measurements. The integrated external quantum efficiencies were calculated from the spectral photoresponse distributions under reverse bias conditions. The modulation-frequency effects on spectral distributions were also investigated. The results were compared for all cells which have different back contacts and excitation intensity.