Low Hysteresis Perovskite Solar Cells Using an Electron-Beam Evaporated WO3–x Thin Film as the Electron Transport Layer

Abstract

Perovskite solar cells utilize metal oxide thin films as electronic transport for high performance devices. These electronic transport metal oxides are generally processed at higher temperatures. In this research we report a room temperature processed WO3–x thin film as the electron transport layer for a high performance and low hysteresis device. The highly oxygen deficient WO3–x film was deposited at room temperature using e-beam evaporation in high vacuum conditions. For comparison, the amount of oxygen vacancies was reduced by postannealing of the as-deposited WO3–x films at 300 °C for 1 h in air. X-ray diffraction and Raman measurements showed no WO3–x characteristic peak of both the as-deposited and annealed films. From X-ray photoelectron spectroscopy and electron paramagnetic resonance, the as-deposited film shows large amounts of oxygen vacancies compared to the postannealed film. The bandgap of the postannealed film increases due to reduced conductivity and thus a reduction in the device performance, mainly because of the low Voc and high current–voltage hysteresis in the forward and reverse scans. The perovskite solar cell device developed using the room temperature deposited electron transport WO3–x layer has shown low current–voltage hysteresis. This device achieved a power conversion efficiency of 10.3% and hysteresis index of 2.1%. This work demonstrates the feasibility of the WO3–x film as an electron transport layer for the high efficiency perovskite solar cell with reduced hysteresis fabricated at low temperature using an industrially viable e-beam evaporation method.