Influence of Oxygen and Nitrogen in the Intrinsic Layer of a-Si:H Solar Cells

Abstract

The effects of oxygen and nitrogen on hydrogenated amorphous silicon (a-Si:H) films and solar cells are systematically studied in the initial and light-soaked states. The oxygen and nitrogen concentrations were varied from 1018 to 1021 cm-3 and 1016 to 1019 cm-3, respectively. In the initial state, dark conductivity and photoconductivity increase, and the activation energy of dark conductivity decreases with increase in the oxygen and nitrogen concentrations, because of the creation of donorlike states. These film properties after light-soaking, however, are independent of the oxygen and nitrogen concentrations, probably because they are dominated by light-induced states. On the other hand, the conversion efficiency of solar cells in both the initial and light-soaked states drops as the oxygen and nitrogen concentrations increase. Collection efficiency measurements show that the electric field distribution in the i-layer is affected by the donorlike states even after light-soaking. The photovoltaic properties of solar cells more sensitively reflect the effect of oxygen and nitrogen incorporation than the film properties.