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CCI Solar Events - October, 2017 Pick date

1 PM

CCI Cybermeeting - Matteo Gerosa - Galli Group - U. Chicago

01:00 PM to 02:00 PM, October 12, 2017

Location: eZuce

Surface oxygen vacancies and two-dimensional charge localization and dynamics in WO3 absorbers for photocatalysis

Continuing our study of photo-absorber surfaces and of their interfaces with water, we took a closer look at tungsten trioxide (WO3). In particular, we investigated defects at the surface, its electronic structure, and the localization properties of excess charge carriers. We considered a realistic model of the experimentally most stable surface of WO3, which presents a high concentration of oxygen vacancies, and we performed density functional theory and ab initio molecular dynamics simulations with dielectric dependent hybrid functionals.

Our results show that the potential energy surface of the defective WO3 surface is highly corrugated, with singlet and triplet states close in energy, and the associated frontier orbitals exhibiting different localization properties. In particular, we identify a two-dimensional spatial distribution of the excess charge at the surface to be energetically most favorable, both at 0K and at finite temperature, and we interpret this result as the evidence of formation of 2D large polarons in this material.

We discuss the importance of such charge localization properties for initiating relevant electrochemical reactions at the surface in the presence of water. Finally, we present results for the band edge positions computed at the GW level, discussing the role of solvation effects in the presence of a water interface.