Atomic Layer Deposition of Defective Amorphous TiO_x Thin Films with Improved Photoelectrochemical Performance

Abstract

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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“…A smaller arc radius shows an efficient charge transfer and a more effective separation of photoinduced charge carriers. 47…”

Rational Design of Photoanodes to Produce Value‐Added Chemicals Coupled with Hydrogen

“…[61] For example, several studies have been published on modifying the bandgap energy of TiO 2 by creating oxygen vacancies, or N-and Hdoping, which enhanced its visible light absorption (Figure 8A,B). [204] Despite the bandgap narrowing of the semiconductors, numerous studies have been published on heteroatom doping to mitigate the inherent limitations such as charge separation and transfer of the semiconductors. In this regard, the PEC performance of porous BiVO 4 photoanode Figure 7.…”

“…[202] All the potential is represented here in RHE (at pH = 0). [204] (Reproduced from reference [204] with permission Copyright 2023, American Chemical Society). (c-e) exhibit the change in bandgap energy upon heteroatom doping in BiVO 4 photoanode [106,107] and (f) shows the improved PEC stability curve by tuning bandgap energy and protective coating on BiVO 4 photoanode.…”

“…Tuning the defect concentration in TiO x thin film: (a) valence band XPS spectra exhibit the difference between the VB positions and fermi levels of ALD-TiO x thin films and (b) schematic diagram illustrating the midgap energy levels of the TiO x -120, TiO x -140, TiO x -160, TiO x -180, and TiO x -200 thin films. The O v indicates oxygen vacancies [204]. (Reproduced from reference[204] with permission Copyright 2023, American Chemical Society).…”