Solution-Processed Ga-Doped ZnO Nanorod Arrays as Electron Acceptors in Organic Solar Cells

This paper reports the utilization of ZnO nanorod arrays (NRAs) doped with various concentrations of Ga (0, 0.5, 1, 2, and 3 at %) as electron acceptors in organic solar cells. The donor, poly(3-hexylthiophene) (P3HT), was spin coated onto Ga-doped ZnO NRAs that were grown on fluorine-doped tin oxide (FTO) substrates, followed by the deposition of a Ag electrode by a magnetron sputtering method. Adjusting the Ga precursor concentration allowed for the control of the structural and optical properties of ZnO NRAs. The short circuit current density increased with increasing Ga concentration from 0 to 1 at %, mainly because of improved exciton dissociation and increased charge extraction. Meanwhile, the reduced charge recombination and lower hole leakage current led to an increase in the open circuit voltage with Ga concentrations up to 1 at %. The device with the optimum Ga concentration of 1 at % exhibited power conversion efficiency nearly three times higher compared to the device without Ga doping. This finding suggests that the incorporation of Ga can be a simple and effective approach to improve the photovoltaic performance of organic solar cells.