Relation between the open-circuit voltage and the band gap of absorber and buffer layers in a-Si:H solar cells

The relation between the open-circuit voltage (Voc) of hydrogenated amorphous silicon (a-Si:H) solar cells and the band gap of the absorber layer has been investigated by changing the substrate temperature of the absorber layer. By decreasing the substrate temperature from 200°C to 150°C the Voc has increased by 0.05V. However, the temperature dependence of the Voc is larger than the change of the optical band gap of individual intrinsic layers, which indicates that also other absorber layer properties play an important role. Using simulations the effect of changing the mobility gap of as well the absorber layer as the buffer layer at the p¿i interface on the performance of a-Si:H solar cells has been investigated. The recombination rate profile in the solar cell at the Voc is a useful tool to analyze and optimize different parts of the solar cell to obtain a high Voc. The simulations confirm the trend of increasing the Voc when implementing absorber layers with a higher mobility gap. The simulations demonstrate that increasing the mobility gap of the buffer layer at the p¿i interface results in a further improvement of the Voc, however an optimal value of the mobility gap is found with respect to the conversion efficiency. Keywords: Hydrogenated amorphous silicon (a-Si:H); Thin film solar cell; Open-circuit voltage; Simulation; Buffer layer