TiO₂/SnO₂ electron transport double layers with ultrathin SnO₂ for efficient planar perovskite solar cells

The electron transport layer (ETL) plays an important role on the performance and stability of perovskite solar cells (PSCs). Developing double ETL is a promising strategy to take the advantages of different ETL materials and avoid their drawbacks. Here, an ultrathin SnO₂ layer of ～ 5 nm deposited by atomic layer deposit (ALD) was used to construct a TiO₂/SnO₂ double ETL, improving the power conversion efficiency (PCE) from 18.02% to 21.13%. The ultrathin SnO₂ layer enhances the electrical conductivity of the double layer ETLs and improves band alignment at the ETL/perovskite interface, promoting charge extraction and transfer. The ultrathin SnO₂ layer also passivates the ETL/perovskite interface, suppressing nonradiative recombination. The double ETL achieves outstanding stability compared with PSCs with TiO₂ only ETL. The PSCs with double ETL retains 85% of its initial PCE after 900 hours illumination. Our work demonstrates the prospects of using ultrathin metal oxide to construct double ETL for high-performance PSCs.