Buried Interface Smoothing Boosts the Mechanical Durability and Efficiency of Flexible Perovskite Solar Cells

Flexible perovskite solar cells (F-PSCs) have the advantages of high power-per-weight, solution processability, and bending durability and have emerged as a competitive photovoltaic technology for various applications. As the core electron transport layer (ETL) in n-i-p-type device configurations, the solution-processed SnO2 generally suffers from serious defect stacking on films, compromising the charge transport properties and the performance of resulting devices. Herein, we proposed a media-filling strategy to optimize the contact quality at the buried interface by introducing Al2O3 nanoparticles on the SnO2 surface. Rather than forming a compact insulating layer, the Al2O3 can fill the grain boundaries of SnO2 and smooth the substrate surface. Optimized interfacial contact under careful concentration control can rationally minimize the contact area of the perovskite with the surface imperfections of SnO2 to mitigate trap-assisted charge recombination. Furthermore, the reduced surface roughness of SnO2 facilitates the uniform deposition and oriented growth of upper perovskite film. As a result, the target F-PSCs achieved an impressive efficiency of 23.83% and retained 80% of the initial performance after 5000 bending cycles at a radius of four mm.