Effect of the Hetero-Interface on the Photoresponse of a-Si/c-Si Solar Cells

Abstract

Heterojunction solar cells were fabricated by glow discharge deposition of amorphous silicon on p-type crystalline silicon resulting in a n/i/p structure. Dark I-V-T data on the devices show that the conduction in the forward bias regime (<0.4 volts) for better devices agrees with a multi-tunnelling-capture-emission process. The photoresponse was evaluated (under 100 mW/cm²) for various a-Si thicknesses and substrate resistivities. Spectral response tests showed an increased low wavelength absorption as the a-Si thickness was decreased. The blue response of the devices have better fill-factors than the red response indicating defects at the interface. Further, I-V-T and C-V measurements also corroborate the presence of defect states which seem to prevent the spread of the depletion region in crystalline silicon. The photoresponse was found to be very sensitive to the interface defects and the fill-factors ranged from 0.42, for the sample in which the depletion region had spread, to 0.1 in those where the depletion region had been reduced in thickness by the interface states.