A bifunctional floral TiO2–TiB2 heterostructure buried interface on SnO2 for 23.5 % efficient n–i–p perovskite solar cells

Interfacial energy mismatch and carrier recombination at the electron transport layer (ETL)/perovskite interface significantly limit the performance of perovskite solar cells (PSCs). We present a bifunctional dual-layer electron transport layer consisting of a floral TiO₂–TiB₂ heterostructure integrated on SnO₂ to address these limitations. The TiO₂–TiB₂ heterostructure, formed through the partial oxidation of hydrothermally produced TiB₂ nanoflakes, exhibits advantageous energy band alignment and provides a robust internal electric field at the buried interface, as confirmed by UPS, Mott–Schottky, and KPFM studies. This facilitates effective charge extraction, diminishes trap-assisted recombination, and improves perovskite crystallization while minimizing lattice strain. The optimized dual-layer ETL attains a power conversion efficiency (PCE) of 23.5 %, with a V_OC of 1.201 V, J_SC of 24.5 mA cm⁻², and a fill factor of 78.81 % in n–i–p structured perovskite solar cells utilizing α-FAPbI₃. Improved charge carrier mobility and reduced trap density were validated by SCLC, TRPL, and EIS studies. The gadget demonstrates outstanding operational and environmental stability under heat, moisture, and prolonged light-stress conditions. This study presents a scalable approach for interfacial engineering of dual-layer electron transport layers to achieve extremely efficient and durable perovskite photovoltaics.