Unveiling and optimizing the role of ALD-SnO2 in Perovskite solar cells

Abstract Tin dioxide (SnO 2 ) is widely used as an electron transport layer (ETL) in perovskite solar cells (PSCs) due to its high electron mobility and stability. While atomic layer deposition (ALD) enables the formation of uniform and defect-free SnO 2 films, its direct contact with perovskite leads to energy level mismatch and charge recombination, limiting device performance. In this study, we systematically investigate the role of ALD-SnO 2 in PSCs and reveal that its direct interface with perovskite induces severe energy loss rather than efficient charge transport. To address this, we examine a double-layer ETL architecture, where a spin-coated SnO 2 nanoparticle layer is deposited on ALD-SnO 2 . Optical and morphological analyses confirm that ALD-SnO 2 alone causes charge trapping, while ALD + SC improves charge extraction and interfacial quality. As a result, PSCs with ALD + SC achieve a power conversion efficiency (PCE) exceeding 22%, significantly outperforming ALD-only and spin-coated-only SnO 2 configurations.