Evaluation of metal oxides prepared by reactive sputtering as carrier-selective contacts for crystalline silicon solar cells

With high quality silicon wafers nowadays available at a low cost, further technology improvement relies on the development of inexpensive and highly efficient carrier-selective contacts (CSC). To this respect, evaporated MoOx hole-selective contacts recently brought some attention due to impressive transparency and carrier selectivity properties, and other materials are widely studied in other photovoltaics technologies (TiO2, WO3, V2O5, ...). Compared to standard heterojunction devices using amorphous silicon as passivating layer and CSC, reported efficiencies for devices using evaporated MoOx layers still fall short due to carrier extraction or recombination issues. Whereas little room for maneuver is foreseen to tune the properties of evaporated metal oxide layers, reactive sputtering on the other hand is expected to allow manipulating the work-function of metal oxides. We will review in this presentation the potential of using reactively sputtered metal-oxides as CSC in c-Si solar cells. Preliminary results obtained with MoOx indicate that decreasing the oxidation state of the layer yields better transport properties but poorer selectivity. Also, though a drastic drop in lifetime was observed after sputtering a MoOx layer on a passivating a-Si layer, annealing enabled a recovery of most of the lifetime.