Hafnium oxide interface stabilization for efficient, photothermally stable perovskite solar cells

Organic molecular layers at both hole- and electron-selective interfaces are essential for achieving high-efficiency perovskite solar cells, yet their limited photothermal stability hinders long-term device operation. We used atomic layer deposition to deposit hafnium oxide (HfO_x) interlayers to stabilize these molecular interfaces under operational stress. At the NiO_x/self-assembled monolayer (SAM) interface, a hydroxyl-rich, Lewis-acidic n-HfO_x layer (n denotes negative fixed-charge polarity) promoted tridentate phosphonic acid coordination and enhanced SAM retention and thermal durability. At the perovskite/C₆₀ interface, the p-HfO_x layer (p denotes positive fixed-charge polarity) anchored 3-fluorophenylethylammonium iodide (3F-PEAI) through Hf⋯F interactions that also acted as a diffusion barrier against halide- and silver-ion migration. Devices achieved a power conversion efficiency of 27.1% (26.6% certified) and retained more than 90% of their initial efficiency for ~5000 hours under 1-sun equivalent illumination at 85°C in ambient air.