Unveiling the dopant segregation effect at hematite interfaces

TL;DR

This paper investigates how Sn and Sb dopant segregation at hematite interfaces affects electronic properties, revealing mechanisms behind efficiency improvements in hematite photoanodes for solar water splitting.

Contribution

It provides a detailed atomic-level analysis of dopant effects on hematite interfaces, linking segregation to electronic structure modifications and efficiency enhancements.

Findings

Dopant segregation reduces potential barriers at grain boundaries.

Surface segregation decreases oxygen vacancy formation energy.

Electronic effects explain the peak efficiency of doped hematite interfaces.

Abstract

Understanding the effects of atomic structure modification in hematite photoanodes is essential for the rational design of high-efficiency functionalizations. Recently it was found that interface modification with Sn/Sb segregates considerably increases hematite photocatalytic efficiency. However, the understanding of the different electronic effects of these modifications at the atomic level is still lacking. This letter describes the segregation effects of two different dopants-Sn and Sb-on both the solid-solid (grain-boundaries) and solid-liquid interfaces (surfaces) of hematite. Within an ab-initio approach, we quantitatively extract the potential barrier reduction on polycrystalline interfaces due to the dopant, which causes an increase in the inter-grain electron transport. Concomitantly, the dopants' segregation on hematite surfaces results in a decrease of the oxygen vacancy formation energy. Such vacancies lead to the experimentally observed rise of the flat-band potential. The comprehension of the electronic effects of dopants on both types of interfaces explains the experimental peak efficiency of interface-modified hematite with dopant segregates, also enabling the control and design of interfaces for different higher-efficiency applications.