Fluorine-Doping of Mesoporous TiO₂ Enables Efficient Defect Passivation for High-Efficiency and Stable Perovskite...

Mesoporous titanium dioxide (m-TiO₂) is widely used as an electron transport layer (ETL) in perovskite solar cells (PSCs), but its large surface area introduces oxygen-vacancy-related trap states that accelerate nonradiative recombination, particularly under low-intensity illumination. Here, we report a sulfur hexafluoride (SF₆) reactive ion etching (RIE) plasma fluorination strategy that passivates oxygen vacancies in m-TiO₂ through the formation of Ti─F bonds. X-ray photoelectron spectroscopy and electron-only-device characterizations confirm a reduced trap density after fluorination. The fluorinated m-TiO₂ (F-doped TiO₂) exhibits increased electrical conductivity, an upward Fermi-level shift, and enhanced surface hydrophobicity, which collectively facilitate the high-quality growth of FAPbI₃ films with larger grains, improved crystallinity, and reduced microstrain. PSCs incorporating F-doped TiO₂ achieve PCEs of 25.13% under one-sun illumination and 36.19% under 1000-lux LED illumination. In addition, wide-bandgap perovskite devices also show improved performance, demonstrating the generality of the fluorination strategy. Unencapsulated devices retain 80% of their initial efficiency after 2000 h of ambient storage, confirming improved long-term stability. These results establish SF₆ RIE plasma fluorination of TiO₂ as a simple and broadly applicable route to enhancing both efficiency and stability in PSCs across diverse operating conditions.