Abstract

• Zinc Oxide (ZnO) nanoparticles were synthesized by the sol-gel technique. As prepared ZnO thin films were deposited by spin coating method on different annealing temperatures at200 °C and 300 °C. Optical properties of ZnO thin films were investigated by Ultraviolet–visible spectroscopy (UV–VIS). Energy gaps were decreased from 3.27 eV at 200 °C to 3.18 eV at 300 °C with increasing temperature. On the contrary, Urbach energy was decreased from 180 meV (300 °C) to 92 meV (200 °C) due to effect of annealing temperature.This mainly comes from decreasing of interatomic spacing and the average potential energy by defects and imperfection of semiconductor materials. Hence, Lower Urbach energy and higher transmittance of ZnO nanoparticles thin film is suitable electron transport layer in low temperature processed for flexible perovskite solar cells