Optimization and fabrication of rear surface passivated c-Si solar cells on 156 cm2 area with local point contacts made by microsecond-pulsed laser firing

Abstract

Fabrication of laser fired contacts using µs-pulsed laser has been studied. In order to achieve damage free contact and low contact resistance in silicon solar cell, pulse length and number of pulses of the laser have been varied and it was observed that 11 µs, 100 pulses provide a good ohmic contact. The contact diameter is as small as 30 µm. As the passivation layer for the p-type rear surface, a-SiONx:H and a-SiONx:H/a-SiNx:H have been explored and these PECVD deposited layers provides excellent passivation leading to effective lifetime as high as 90 µs or more with the Cz wafers. Solar cells were fabricated on 12 cm2 and 16 cm2 area using Cz wafers with the rear side point contacts were realised by the laser firing of Al film deposited by electron-beam or thermal evaporation. On 16 cm2 area, Voc value as high as 628 mV has been obtained after annealing at 375 °C for 20 min. However, these cells suffered from low fill factor. Finally, cells were also fabricated on 156 cm2 area with LFC using 0.3 mm of contact pitch. Fill factor of 77.3% has been achieved with LFC metallization fraction of 0.8% at the rear surface. An efficiency of 15.8% was obtained. By avoiding the edge losses, a FF enhancement to 78.9% was observed using smaller cells of 100 cm2 area.