Thin Films of Tin Oxide Nanosheets Used as the Electron Transporting Layer for Improved Performance and Ambient Stability of Perovskite Photovoltaics

Inorganic semiconducting metal oxide electron transporting layers (ETLs) with tailored nanostructures have the potential to yield efficient perovskite solar cells (PSCs) with improved stability and reduced hysteresis. Here, a simple and facile hydrothermal protocol is demonstrated for the growth of crystalline SnO₂ nanosheet (SNS) thin films with excellent optical and photoelectrical properties. When applied as ETLs, the SNS enhances light harvesting, boosts charge collection, reduces hysteresis and improves the ambient stability. Moreover, optimization of the interfacial properties between the SNS and the perovskite layer by the introduction of a C₆₀ interlayer results in better energy level alignment, decreasing charge recombination and thus prolonging the electron lifetime and improving the open-circuit voltage (V_oc). Therefore, the efficient conventional n-i-p PSCs based on C₆₀-modified SNS ETLs have almost hysteresis-free behavior, with a champion power conversion efficiency, PCE, of 18.31% and a stabilized PCE over 18.00%. The SNS-based PSC exhibits respectable ambient stability retaining over 90% of its initial efficiency after being stored in air at room temperature for 500 h without encapsulation. Such robust SNS ETLs pave the way to low-cost and stable PSCs with high efficiency, less hysteresis, and long-term stability.