High-Quality van der Waals Epitaxial CsPbBr_(3)Film Grown on Monolayer Graphene Covered TiO_(2)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 highquality perovskite films.Herein,we succeeded in obtaining higher-quality CsPbBr_(3)films by introducing large-area monolayer graphene as a stable physical overlay on top of TiO_(2)substrates.Benefiting from the inert and atomic smooth graphene surface,the CsPbBr_(3)film grown on top by the van der Waal epitaxy has higher crystallinity,improved(100)orientation,and an average domain size of up to 1.22μm.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 CsPbBr_(3)film is fabricated,exhibiting power conversion efficiency(PCE)of up to 10.64%and stability over 2000 h in the air.