High-Quality van der Waals Epitaxial CsPbBr₃ Film Grown on Monolayer Graphene Covered TiO₂ for High-Performance Solar Cells

Two-dimensional materials have been widely used to tune the growth and energy-level alignment of perovskites. However, their incomplete passivation and chaotic usage amounts are not conducive to the preparation of high-quality perovskite films. Herein, we succeeded in obtaining higher-quality CsPbBr₃ films by introducing large-area monolayer graphene as a stable physical overlay on top of TiO₂ substrates. Benefiting from the inert and atomic smooth graphene surface, the CsPbBr₃ film grown on top by the van der Waal epitaxy has higher crystallinity, improved (100) orientation, and an average domain size of up to 1.22 μm. Meanwhile, a strong downward band bending is observed at the graphene/perovskite interface, improving the electron extraction to the electron transport layers (ETL). As a result, perovskite film grown on graphene has lower photoluminescence (PL) intensity, shorter carrier lifetime, and fewer defects. Finally, a photovoltaic device based on epitaxy CsPbBr₃ film is fabricated, exhibiting power conversion efficiency (PCE) of up to 10.64% and stability over 2000 h in the air.