Low temperature Zn-doped TiO2 as electron transport layer for 19% efficient planar perovskite solar cells

Abstract

The properties of the perovskite solar cells (PSCs) are highly correlated with Fermi level, trap-state density and conductivity of inorganic electron transport layer. Metal elemental doping is an effective solution to largely improve the property of oxide semiconductor thin film. In this study, zinc dopant is successfully inserted into TiO2 crystal lattice using low-temperature solution-processed route. We find that Zn-doped TiO2 films possess less trap-state density and better conductivity, compared to undoped thin films, which contributes to the promotion of short circuit current. Ultraviolet photoelectron spectroscopy displays inserting Zn2+ into TiO2 compact layer can lift up TiO2′s Fermi level, which reasonably improved the carrier dissociation and transportation. Consequently, CH3NH3PbI3 PSCs based on 4.5% Zn-doped TiO2 has obtained 17.6% power conversion efficiency (PCE), which is nearly 27.5% higher than control device (13.8%). In addition, triple-cation mixed-halide PSCs based on 4.5% Zn-doped TiO2 has obtained a PCE of 19.04%, which is almost 13.7% higher than PCE of the device with undoped sample 16.75%. These findings offer a potential low-temperature doping method in TiO2 ETL for flexible high-performance PSCs.