A new strategy for buried 2D/3D heterojunctions in perovskite solar cells

• • The in situ solid-state ligand-exchange strategy confines 2D perovskite formation exclusively at the SnO2/perovskite interface, eliminating 2D-phase contamination in the 3D bulk, which is critical for maintaining high open-circuit voltage and fill factor in scalable PSCs. • • Thioglycolic acid (TGA) capping on SnO2 nanoparticles enhances alkylamine adhesion via acid-base reaction, achieving a uniform and tightly bound ligand layer that prevents ligand diffusion into the perovskite bulk, a common failure mode in prior methods. • • In situ photoluminescence (PL) spectroscopy reveals that the target substrate (SnO2-TGA-OAm) induces a prolonged PL increase phase during annealing, indicating suppressed non-radiative recombination and improved crystallinity, which correlates with higher carrier lifetimes and reduced trap densities. • • The method leverages the binding affinity between –SH and SnO2, providing a robust anchoring mechanism that overcomes the limitations of SAM-based approaches, which suffer from low packing density and non-uniformity, thereby enabling more reproducible device fabrication.