Polyacrylonitrile-Boosted Surface Coverage of 2D WSe ₂ at the SnO ₂ /Perovskite Interlayer for High-Performance Perovskite Solar Cells

Two-dimensional transition-metal dichalcogenides (TMDs) (2D TMDs) have emerged as promising interlayer materials between SnO₂ electron transport layer (ETL) and perovskite absorbers as they can effectively modulate the energy levels of SnO₂ and facilitate the growth of perovskite crystals. However, the limited affinity of 2D TMDs for the SnO₂ surface can result in inadequate coverage, which can adversely affect the performance of perovskite solar cells (PSCs). This study addresses this issue by incorporating polyacrylonitrile (PAN) to enhance the surface affinity of 2D tungsten selenide (WSe₂). By utilizing the excellent dispersibility of the polymer, the PAN-WSe₂ composite film achieves uniform dispersion and high surface coverage on the SnO₂ layer. WSe₂ features surface free of dangling bonds, a tunable electronic band structure, adjustable functional groups, and intrinsic compactness. These characteristics enable WSe₂ to regulate SnO₂'s energy levels, passivate defects in the SnO₂ ETL and functional layer, and alleviate interfacial stress due to its lattice matching with perovskite. This synergy results in perovskite films exhibiting higher crystallinity and lower defect density. Compared to SnO₂-based PSCs, PAN-WSe₂-modified PSCs demonstrate a significant enhancement in the power conversion efficiency, achieving an open-circuit voltage (V_OC) of 1.18 V. Furthermore, after storage in nitrogen for 3800 h, PAN-WSe₂-based PSCs retain 95% of their initial efficiency, highlighting their stability and potential for long-term applications.