The usage of TiO₂ in perovskite solar cells is always faced with the risk of device decomposition due to its high photocatalysis activity. To deal with this problem, here in this work, a strategy of in situ surface passivation was proposed and performed on TiO₂. After spin-coating Ca(OH)₂ solution on a TiO₂ mesoporous scaffold and annealing, the surface layer of the scaffold was converted into CaTiO₃, as confirmed by X-ray photoemission spectroscopy and X-ray diffraction studies. The modified TiO₂ scaffold was then used as an electron-transport-material in perovskite solar cells. It was observed that after moderate modification, the short-circuit current density increased from 22.32 (±0.25) to 23.19 (±0.28) mA/cm², the open-circuit voltage rose from 1.042 (±0.009) to 1.080 (±0.011) V, and the fill factor increased from 63.89 (±1.95)% to 71.37 (±0.43)%, leading to an improvement from 14.92 (±0.36)% to 17.88 (±0.37)% of the power conversion efficiency. Transient photocurrent/photovoltage decay curves and impedance spectroscopy tests showed that moderate modification accelerated charge extraction while it retarded charge recombination. Besides, the in situ CaTiO₃ layer prolonged the device stability. After being stored in the dark for 46 days (relative humidity of 30%), 92.6% of the initial efficiency was reserved, compared to that of 68.4% for the control devices. Designated UV irradiation showed that the surface passivation retarded the photocatalysis activity of TiO₂, which contributed to the prolonged device stability.