| Summary: | In this study, spatial atomic layer deposition (sALD) is employed to prepare titanium dioxide (TiO<sub>2</sub>) thin films by using titanium tetraisopropoxide and water as metal and water precursors, respectively. The post-annealing temperature is varied to investigate its effect on the properties of the TiO<sub>2</sub> films. The experimental results show that the sALD TiO<sub>2</sub> has a similar deposition rate per cycle to other ALD processes using oxygen plasma or ozone oxidant, implying that the growth is limited by titanium tetraisopropoxide steric hindrance. The structure of the as-deposited sALD TiO<sub>2</sub> films is amorphous and changes to polycrystalline anatase at the annealing temperature of 450 °C. All the sALD TiO<sub>2</sub> films have a low absorption coefficient at the level of 10<sup>−3</sup> cm<sup>−1</sup> at wavelengths greater than 500 nm. The annealing temperatures of 550 °C are expected to have a high compactness, evaluated by the refractive index and x-ray photoelectron spectrometer measurements. Finally, the 550 °C-annealed sALD TiO<sub>2</sub> film with a thickness of ~8 nm is applied to perovskite solar cells as a compact electron transport layer. The significantly enhanced open-circuit voltage and conversion efficiency demonstrate the great potential of the sALD TiO<sub>2</sub> compact layer in perovskite solar cell applications.
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