Lone pair driven anisotropy in antimony chalcogenide semiconductors

TL;DR

This study reveals that the anisotropic crystal structures of antimony chalcogenides are driven by lone pair activity, affecting their electronic properties and offering insights for optimizing solar cell performance.

Contribution

It demonstrates that inter-ribbon interactions in Sb2X3 are beyond van der Waals forces and are influenced by lone pair stereochemistry, challenging previous classifications.

Findings

Inter-ribbon interactions are beyond van der Waals in Sb2X3.

Lone pair stereochemistry drives structural anisotropy.

Anisotropy impacts electronic and optical properties.

Abstract

Antimony sulfide (Sb2S3) and selenide (Sb2Se3) have emerged as promising earth-abundant alternatives among thin-film photovoltaic compounds. A distinguishing feature of these materials is their anisotropic crystal structures, which are composed of quasi-one-dimensional (1D) [Sb4X6]n ribbons. The interaction between ribbons has been reported to be van der Waals (vdW) in nature and Sb2X3 are thus commonly classified in the literature as 1D semiconductors. However, based on first-principles calculations, here we show that inter-ribbon interactions are present in Sb2X3 beyond the vdW regime. The origin of the anisotropic structures is related to the stereochemical activity of the Sb 5s lone pair according to electronic structure analysis. The impacts of structural anisotropy on the electronic and optical properties are further examined, including the presence of higher dimensional Fermi surfaces for charge carrier transport. Our study provides guidelines for optimising the performance of Sb2X3-based solar cells via device structuring based on the underlying crystal anisotropy.