Sputter-Coated TiO₂ Films as Passivation and Hole Transfer Layers for Improved Energy Conversion with Solar Fuel...

Area of Science:

• Materials Science
• Electrochemistry
• Renewable Energy

Background:

• Atomic-layer-deposited (ALD) "leaky" TiO2 is recognized for charge-selective protection in semiconductor solar fuel electrodes.
• WO3/CuWO4 type-2 heterojunctions are investigated for water oxidation photoanodes.

Purpose of the Study:

• To demonstrate, for the first time, the use of sputter-deposited TiO2 as hole-selective contacts for WO3/CuWO4 photoanodes.
• To investigate the effect of TiO2 layer thickness on photoelectrochemical performance and stability.

Main Methods:

• Radio frequency (RF) magnetron sputtering was used to deposit TiO2 films of varying thicknesses (2-128 nm).
• Characterization included Raman spectroscopy and powder X-ray diffraction (XRD) to confirm amorphous structure.
• Photoelectrochemical (PEC) scans and vibrating Kelvin probe photovoltage (SPV) spectroscopy were employed to evaluate performance.

Main Results:

• Thin TiO2 layers (2-8 nm) nearly doubled photocurrent to 0.97 mA cm-2 and increased surface photovoltage by 25%.
• Amorphous TiO2 films improved WO3/CuWO4 effective band gap and suppressed surface recombination defects.
• Thicker TiO2 films (16-128 nm) showed reduced performance due to increased hole transfer resistance and light shading.
• TiO2 coatings enhanced photoelectrode stability, maintaining O2 evolution over 3 hours.

Conclusions:

• RF magnetron sputtering is an effective method for depositing amorphous TiO2 passivation layers for WO3/CuWO4 solar fuel photoelectrodes.
• Optimized TiO2 thickness is crucial for maximizing photocurrent and photovoltage.
• Combined PEC and SPV measurements offer valuable insights into the function of TiO2 coatings in photoelectrochemical systems.