Fluorine‐Doping of Mesoporous TiO 2 Enables Efficient Defect Passivation for High‐Efficiency and Stable Perovskite Solar Cells

ABSTRACT Mesoporous titanium dioxide (m‐TiO 2 ) 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 (SF 6 ) reactive ion etching (RIE) plasma fluorination strategy that passivates oxygen vacancies in m‐TiO 2 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‐TiO 2 (F‐doped TiO 2 ) exhibits increased electrical conductivity, an upward Fermi‐level shift, and enhanced surface hydrophobicity, which collectively facilitate the high‐quality growth of FAPbI 3 films with larger grains, improved crystallinity, and reduced microstrain. PSCs incorporating F‐doped TiO 2 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 SF 6 RIE plasma fluorination of TiO 2 as a simple and broadly applicable route to enhancing both efficiency and stability in PSCs across diverse operating conditions.