Bulk and Surface Defect Manipulation of the ZnO ETL for All-inorganic CsPbBr3 Perovskite Solar Cells

Abstract

Electron transport layer (ETL) in the traditional CsPbBr3 perovskite solar cells (PSCs) without hole transport layer (HTL) presents the capability to transport electrons and to block hole transport, which radically affects the photovoltaic performance of PSCs. However, ZnO ETL prepared by classic sol-gel method exhibits obvious drawbacks, such as serious interfacial recombination reaction, inducement of oxygen vacancy (VO) and zinc interstitials (Zni). Herein, we demonstrate that alkali metal chloride (e.g. KCl), serving as the passivating agent for the surface and bulk phase, can promote surface modification and doping in ZnO ETL, respectively. The experimental results show that the interaction between K+ and Zn2+, and the occupation of VO by Cl-, suppress the internal defect states of ZnO films, which enhances the crystal coordination between ZnO and CsPbBr3, and improves the film morphology as well as the quality of the upper perovskite (PVK) films. The experimental PSCs based on the doping approach have achieved the champion power conversion efficiency (PCE) of 9.22%, which ranks the highest PCE of (FTO/ITO)/ZnO /CsPbBr3/Carbon structure. Moreover, the unpackaged devices of the two experimental PSCs still maintain 97.15% and 74.76% of the original PCE after 28 days exposed in the ambient environment, showing the powerful effect of KCl on the regulation of surface and bulk phase defects in the ZnO ETL.