Thick TiO₂-Based Top Electron Transport Layer on Perovskite for Highly Efficient and Stable Solar Cells

Simultaneously achieving high efficiency, long-term stability, and robust fabrication with good reproducibility in perovskite solar cells (PVSCs) is essential for their practical applications. Herein, we first demonstrate a thick TiO2 backbone film directly on top of a perovskite film through a simple room-temperature solution process. Through the strategy of decorating the TiO2 film with fullerene for passivating traps and filling voids, we achieve a fullerene-decorated TiO2 electron transport layer (ETL) in inverted PVSCs. Because of the suppressed monomolecular Shockley–Read–Hall recombination and ion diffusion of the fullerene-decorated TiO2 ETL, stabilized efficiencies of ∼20% and shelf life stability remaining over 98% of initial efficiency after aging in ambient conditions or 16 months are achieved. Remarkably, the PVSCs are insensitive to TiO2 thickness from 50 to 250 nm, which contributes significantly to the robust fabrication and high reproducibility of the PVSCs. This work provides an ETL design on top of a perovskite film for simultaneous improvement of PVSC efficiency, stability, and reproducibility.