Site-Selective Excitation of Defects Promotes Ultrafast Hot-Electron Transfer at the Semiconductor Interface

Area of Science:

• Materials Science
• Photocatalysis
• Surface Chemistry

Background:

• Defect engineering optimizes photocatalyst light absorption and charge trapping for better solar energy conversion.
• The mechanism of photoinduced charge transfer from defects to adsorbed species is poorly understood.
• Direct detection of hot-charge transfer from semiconductor photocatalysts to adsorbed molecules remains elusive.

Purpose of the Study:

• To investigate the mechanism of photoinduced charge transfer from defects to surface-adsorbed species.
• To directly detect hot-charge transfer in a semiconductor-adsorbate system.
• To elucidate the role of Ti3+ defects in rutile TiO2 for interfacial charge transfer.

Main Methods:

• Time-resolved photoelectron spectroscopy (TRPES) for ultrafast dynamics.
• First-principles calculations for theoretical insights.
• Site-selective excitation of Ti3+ defects in rutile TiO2 with adsorbed acetone.

Main Results:

• Demonstrated ultrafast hot-electron transfer (approximately 15 femtoseconds) from rutile TiO2 to acetone.
• Identified Ti3+ defects as the crucial mediators for this electron transfer via d-d excitation.
• Observed suitable interfacial level alignment and strong electronic coupling due to Ti3+ 3d excited states and hybridization with acetone orbitals.

Conclusions:

• Directly detected ultrafast hot-electron transfer from semiconductor defects to adsorbed molecules.
• Defect-mediated hot-electron transfer is a viable mechanism for enhancing photocatalytic performance.
• This phenomenon may be general in adsorbate/semiconductor systems for efficient light harvesting.