A proper control of defects in TiO₂ thin films is challenging work for enhancing the photoelectrochemical (PEC) efficiency in water splitting processes. Additionally, a deep understanding of how defects affect the PEC performance of TiO₂ thin films is of great interest for achieving better performance. With these aims, we prepared defective amorphous TiO_x thin films at various growth temperatures by atomic layer deposition using tetrakis(dimethylamido)titanium as the Ti precursor. Careful X-ray photoelectron spectroscopy and electron spin resonance spectroscopy analyses revealed that the defect concentration in the TiO_x thin films can be controlled by adjusting the growth temperature during the ALD process. We also evaluated the light absorption properties of the deposited TiO_x thin films using ultraviolet-visible absorption spectroscopy. And it was found that the TiO_x thin film deposited at a growth temperature of 200 °C exhibited the highest defect concentration and the highest photocurrent density of 0.051 mA/cm² at 1.23 V vs reversible hydrogen electrode (RHE) compared to those of the other films. The light absorption efficiency, photogenerated charge separation efficiency, and charge transfer efficiency of defective amorphous TiO_x thin films were carefully studied to understand the correlation between the defect concentration in the prepared TiO_x thin film and its PEC activity. This study provides insight into the PEC properties of defective amorphous ALD-TiO_x thin films.

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