Correlation of light-induced enhancement of open-circuit voltage and structural change of heterogeneous silicon solar cells

We observe a significant light-induced increase in the open-circuit voltage, V-oc, of thin-film silicon solar cells whose intrinsic (i) layer consists of an amorphous and microcrystalline mixed phase. The increase depends on the i-layer thickness, the i-layer deposition temperature, the initial V-oc values, and the light-soaking intensity. An increase of as large as 150 mV is observed. The original V-oc is restored after subsequent thermal annealing. In-situ photoluminescence (PL) spectroscopy is used to investigate this metastable phenomenon. We find that the PL intensity and peak-energy position associated with the amorphous component of the heterogeneous material increase upon light soaking, suggesting a structural change. We propose that a reduction of microcrystalline volume fraction or size is responsible for the V-oc enhancement.