On the mechanism of light-induced open-circuit voltage increase in mixed-phase hydrogenated silicon solar cells

Microstructure changes have been proposed to account for the light-induccd open-circuit voltage (V-oc) increase in mixed-phase hydrogenated silicon solar cells. However, recent studies by Raman and X-ray diffraction found no observable change before and after light soaking. In this paper, we propose a two-diode equivalent-circuit model to alternatively explain the dependence of V-oc on the fraction of microcrystalline phase and light-induced V-oc increase in mixed-phase silicon solar cells. We find that not only a reduction of microcrystalline volume fraction or grain size but also a degradation of microcrystallite quality can cause the observed light-induced V-oc increase. A new experimental result with a thin hydrogenated amorphous silicon layer inserted between the mixed-phase intrinsic layer and p layer is satisfactorily explained on the basis of the new model.