Spectral photocurrent-voltage characteristics of crystalline silicon and amorphous silicon solar cells

Abstract

Abstract Crystalline silicon (c-Si) and amorphous silicon (a-Si) solar cells represent complementary cell types. The generation of photocarriers takes place in the semiconductor bulk (c-Si cell) or is confined to the barrier layer (a-Si cell). Carrier collection hence relies on diffusion (c-Si cell) or drift (a-Si cell). We explain the different behavior of the two cell types by measuring photocurrent-voltage characteristics. The photocurrent of the a-Si barrier cell changes its sign at a certain transition voltage U T . We find that U T depends slightly on the light wavelength λ but remains invariant with respect to alterations in the light intensity. It is possible to interpret both features in terms of a suitable uniform-field picture for a-Si p-i-n cells. The field through the i layer reverses its sign at the flat-band voltage U F . A vanishing field reveals the small contribution of diffusion to the photocarrier transport. The function U T (λ) stems therefore from diffusion.