Titanate hollow nanospheres as electron-transport layer in mesoscopic perovskite solar cell with enhanced performance

Nanostructured inorganic oxide semiconductor, working as an electron-transport layer (ETL), greatly affects the power conversion efficiency (PCE) of organometal-halide perovskite solar cell. In this study, as ETLs for mesoscopic perovskite solar cells, titanate hollow nanospheres were synthesized by a simple process that required a cation-exchanging step. Zn2+, Ba2+ and H+ were induced to tune the properties of titanate spheres, and thus the PCE. The conductivity, optical band gap, valence band and conduction band of hollow nanospheres significantly varied with different cations. Optimized devices based on Ti-Zn-O hollow nanospheres presented a PCE of 17% (average efficiency of 16.39%), outperforming the devices with pristine TiO2 spheres (15.87%, average efficiency of 15.08%) and Ti-Ba-O hollow nanospheres (4.88%). Impedance spectroscopy measurements revealed that the enhancement in PCE was ascribed to the improved carrier transport properties and better band matching with the perovskite layer obtained by introducing Zn2+ cations into the TiO2 matrix. This study focuses on developing high-quality inorganic ETL materials for perovskite-based photovoltaic devices.