α-Fe₂O₃/SnO₂ electron transport bilayer for efficient and stable perovskite solar cells

The hybrid metal halide perovskite solar cells (PSCs) have drawn substantial interest owing to their high absorption coefficient and affordable fabrication techniques. Outstanding photovoltaic efficiency has been attained by PSCs based on the SnO₂ electron transport layer (ETL). Nevertheless, there are several issues with the commercial SnO₂ ETLs. An efficient approach to overcome the inherent constraints of a single-layer electron transport layer (ETL) in the fabrication of PSC is to develop a bilayer architecture by combining two distinct types of ETLs with complementary advantages. In order to inhibit interfacial recombination, we present an effective interlayer of hematite (α-Fe₂O₃) between SnO₂ and the metal electrode in this work. It is possible to successfully reduce the defects of the α-Fe₂O₃ layer alone by using the α-Fe₂O₃/SnO₂ electron transport bilayer. With a negligible hysteresis index of 0.03, the optimized α-Fe₂O₃/SnO₂ bilayer ETL in PSC demonstrated outstanding power conversion efficiency (PCE) of 18.24%, J_SC of 21.29 mA.cm⁻², and FF of 75.13%. Additionally, the best device demonstrated exceptional stability, holding onto 91% of the original PCE after 30 days affirming the impeccable insertion of the α-Fe₂O₃/SnO₂ bilayer. Improved electron transfer efficiency, reduced interfacial recombination, and smooth surface morphology contributed towards the enhanced photovoltaic performance of the α-Fe₂O₃/SnO₂ bilayer ETL-based-PSC. The path toward novel ETLs for the fabrication of effective and photo-stable PSCs is provided in this study.