Potentials and development of amorphous silicon carbide heterojunction solar cells

In this paper the potential of amorphous silicon carbide used as an emitter for silicon heterojunction solar cells is presented. Especially the annealing behaviour of the open-circuit voltage V_oc of n-doped amorphous silicon carbide heterojunction emitter solar cells is investigated in detail. We present our results of a significant open-circuit voltage improvement of more than 100 mV on both a flat and a textured front surface triggered by thermal annealing on a hot plate. The observed open-circuit voltage behaviour can be described best by a stretched exponential function, which in general describes relaxation rates in complex systems. Further we investigated the optimum conditions of a post deposition annealing step in order to reach the highest efficiency. During this analysis we also observed deterioration in solar cell performance when the structure is annealed for a very long time. In conclusion, we suppose that a diffusion of weakly bonded or free hydrogen, activated by the annealing which saturates dangling bonds in the amorphous layer itself and most likely more important at the heterojunction interface, is responsible for the strong improvement in V_oc and efficiency.