Ru-Doping in TiO2 electron transport layers of planar heterojunction perovskite solar cells for enhanced performance

Abstract

TiO₂ is widely used as an electron transport layer (ETL) material for perovskite solar cells, and various methods have been used to engineer the properties of TiO₂ ETLs for further improving the performance of perovskite solar cells. In this study, compact Ru-doped TiO₂ films, prepared via a one-step spray pyrolysis method, have been employed as ETLs for planar perovskite solar cells. Compared to the pristine TiO₂ film, the doped counterpart exhibits remarkably improved conductivity, as revealed by the conducting atomic force microscopy measurement. Consequently, the optimized device containing a 1% Ru-doped TiO₂ ETL presents a power conversion efficiency (PCE) of up to 15.7% (with an average value of 14.74%), which is 17% higher than that of the device using the pristine TiO₂ layer (13.42%, with an average value of 12.20%). The mechanism behind the enhancement in photovoltaic parameters has been investigated intensively via physicochemical characterization. A slight upshift of the conduction band minimum (CBM) is observed in the case of Ru-doped TiO₂ films. More importantly, fast injection of the photo-generated electrons from a perovskite layer into an ETL is also found when Ru-doped TiO₂ is applied as the ETL. Meanwhile, impedance spectroscopy suggests that the application of Ru-doped TiO₂ films leads to an increase in recombination resistance and a decrease in selective contact resistance. The enhancement in PCE is attributed to the improved charge injection and transport properties of the Ru-doped TiO₂ film, as well as its better band matching with the perovskite layer. These results demonstrate that doping TiO₂ ETLs with Ru is an efficient approach to improve the photovoltaic performance of perovskite solar cells. The presented work will provide a potential approach for developing materials with high-quality electron transport layers for efficient perovskite-based photovoltaic devices.