Dependence of efficiency of shallow junction silicon solar cells on substrate doping

Abstract

Experimental evidence is provided to support a modification of solar cell theory to include the field-enhanced junction recombination dark current. This term is shown to become more important in limiting shallow junction solar cell efficiency as base resistivity is decreased. The anomalously high-diffusion dark current in the /i-region is also significant in limiting open-circuit voltage. This excess dark current is shown to result from high-surface recombination at the metallic contacts on the front surface (STa = 4 x 10 cm/s, SCr = 7 x 10 cm/s) along with bandgap narrowing and high Auger volume recombination in the diffused /i-region caused by high donor density. It is also pointed out that the effective thickness of the /i-region is substantially less than the junction depth. Methods are proposed for reducing the magnitude of both dark currents to improve overall cell performance.