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 SnO 2 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 Al 2 O 3 nanoparticles on the SnO 2 surface. Rather than forming a compact insulating layer, the Al 2 O 3 can fill the grain boundaries of SnO 2 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 SnO 2 to mitigate trap-assisted charge recombination. Furthermore, the reduced surface roughness of SnO 2 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.