Surface modification of electron transport layers based on TiO2 nanorod boosts efficiency of perovskite solar cells

In this work, TiO2 heterostructure thin films including rutile TiO2 nanorods (TNRs) and anatase TiO2 nanoparticles (TNPs) on fluorine-doped tin oxide (FTO) glass are fabricated by the hydrothermal method and are applied as electron transport layers (ETLs) in MAPbI(3)-based perovskite solar cells (PSCs). To enhance the surface area of ETL, TNRs are first etched in acidic solution by another hydrothermal process for different reaction times before coating with TNPs. The morphological and structural properties of TNRs after etching are carefully investigated. Interestingly, the surface modification of TNR thin film by appropriate TNP deposition and etching improves significantly the efficiency of PSC devices by more than 1.6 times. To further improve the performance of PSC, phenyl-C61-butyric acid methyl ester (PCBM) is used to enhance the charge transfer efficiency at the ETL/perovskite interface, and the optimal PSC device shows the champion efficiency of 18.50% with low charge transfer resistance (11.56 ohms).