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.