Fig. 6

a Variation of EQE of a-Si:H thin film solar cell with growth time of ZnO nanorods. The long growth leads to a denser and larger nanorods, providing a longer optical path, which in turn enhances the collection of efficiency at longer wavelengths. This is demonstrated by up to ~2.5 times increase in the EQE at 750 nm. The rise in the EQE is accompanied with reduction in the solar cell’s FF. This reduction can be attributed to increase in the series resistance due to the increase in density and size of ZnO nanorods. b Variation in the FF of the cells with series resistance extracted from the I–V characteristics of PV device. The series resistance corresponds to the overall device series resistance. Each point in the graph relates to a different ZnO growth time. Here, longer ZnO growth time results in increased series resistance and reduced fill factor