Effects of seed layer on growth of ZnO nanorod and performance of perovskite solar cell

Effects of seed layer on growth of ZnO nanorod and photovoltaic performance of perovskite solar cell were investigated. Three different coating solutions (the clear solution, the colloidal solution, and the nano-powder dispersed solution) were prepared for making seed layers. Vertically aligned ZnO nanorods were grown on the colloidal-based seed layer, while tilted nanorods were obtained on the solution- and powder-based seed layers. Open-circuit voltage (V_oc) of the CH₃NH₃PbI₃ perovskite solar cell was predominantly influenced by the seed layers, where highest V_oc was obtained from the ZnO nanorod grown on the colloidal seed layer. Impedance spectroscopic study revealed that recombination resistances at the seed layer contact and the ZnO nanorod/perovskite interface were increased by the colloidal coating, which was responsible for the enhanced V_oc. Surface modification of ZnO nanorods improved further V_oc and fill factor, leading to power conversion efficiency of 14.35%. This work emphasizes that the seed layer in the ZnO nanorod-based perovskite solar cell plays a major role in determining photovoltage and the ZnO nanorod/perovskite interface gets partly involved in this role.