Overcoming the SnO2 bottleneck in perovskite solar cells: Strategies for enhancing efficiency and stability

Charge transport layers, which selectively transport electrons and holes, are critical to the performance and stability of perovskite solar cells (PSCs). Tin oxide (SnO 2 ) possesses distinctive advantages over the frequently used titanium dioxide (TiO 2 ) as an electron transport layer (ETL), supporting superior photovoltaic conversion efficiency and operational stability in PSCs. Nevertheless, state-of-the-art PSCs incorporating TiO 2 ETLs still demonstrate marginally superior practical performance, highlighting the need to address the limitations of SnO 2 to unlock its full potential. In this review, we examine PSCs employing SnO 2 ETLs with power conversion efficiencies (PCEs) exceeding 24 %, identifying their common characteristics and limitations. We critically analyze various strategies adopted in high-efficiency PSCs, including buried interfaces, self-assembled molecules, organic ligands, molecular bridging, and solvent engineering, and highlight the major challenges associated with SnO 2 ETLs from the perspective of scalability and commercialization.