Low-temperature-processed metal oxide electron transport layers for efficient planar perovskite solar cells

As a promising photovoltaic technology, perovskite solar cells(pero-SCs) have developed rapidly over the past few years and the highest power conversion efficiency is beyond 25%. Nowadays, the planar structure is universally popular in pero-SCs due to the simple processing technology and low-temperature preparation.Electron transport layer(ETL) is verified to play a vital role in the device performance of planar pero-SCs. Particularly, the metal oxide(MO) ETL with low-cost, superb versatility, and excellent optoelectronic properties has been widely studied. This review mainly focuses on recent developments in the use of low-temperature-processed MO ETLs for planar pero-SCs. The optical and electronic properties of widely used MO materials of TiO_(2), ZnO, and SnO_(2), as well as the optimizations of these MO ETLs are briefly introduced. The commonly used methods for depositing MO ETLs are also discussed. Then, the applications of different MO ETLs on pero-SCs are reviewed.Finally, the challenge and future research of MO-based ETLs toward practical application of efficient planar peroSCs are proposed.