Intensity dependence of quantum efficiency and photo-gating effects in thin film silicon solar cells

Abstract

Steady-state photoconductivity measurements have been carried out on thin-film silicon pin structures of i-layer thickness typically 4 μm, where crystalline composition has been varied by adjustment of the silane concentration in the process gas. In amorphous and low-crystallinity cells, strongly-absorbed light incident from the p-side at photon fluxes in excess of 1014 cm-2 s-1 produces strongly sub-linear intensity dependence, ‘S’ shaped reverse current- voltage curves and amplification of a second weakly-absorbed beam, termed photogating. These effects are linked to the formation of space charge and attendant low-field region close to the p-i interface, as confirmed by computer simulation. More crystalline devices exhibit little or no such behaviour....