Suppressing recombination in perovskite solar cells via surface engineering of TiO2 ETL

Hybrid perovskite solar cells (PSCs) have gained significant attention owing to their excellent physicochemical and photovoltaic properties. PSCs typically consist of a perovskite light absorber sandwiched between two carrier selective layers optimized with respect to optimal band alignment and low interfacial recombination. The quality of the perovskite layer and interfaces play major roles in the fabrication of high-performance PSCs. In the present work, we systematically investigate the planar structure PSCs based on TiO2 and TiO2/ZnO electron transport layers (ETLs), which provide deeper insight into the charge recombination and accumulation mechanisms. We show that the double-layer structure of TiO2/ZnO ETL improves the optical and morphology properties of perovskite film leading to superior device performance. From the ideality factor, EIS and IMVS results, a suppressed recombination in TiO2/ZnO PSCs is achieved, which is due to improved grain size of perovskite absorber layer grown on ZnO nanocrystals (NCs). Additionally, we find that the ZnO NCs improve the shunt resistance and quality of the perovskite and suppress the recombination. The present study provides a novel strategy to improve the device performance of PSCs along with a detail investigation procedure to understand the physical mechanism.