Tunability of electronic and optical properties of the Ba-Zr-S system via dimensional reduction

TL;DR

This study investigates how reducing dimensionality in Ba-Zr-S transition metal sulfide perovskites alters their electronic and optical properties, revealing tunability through Ruddlesden-Popper phase formation.

Contribution

It demonstrates that dimensional reduction in Ba-Zr-S compounds shifts band gaps from direct to indirect and enhances anisotropic optical properties, offering a new tuning strategy.

Findings

Ruddlesden-Popper phases have lower fundamental band gaps.

Layered compounds exhibit significant optical anisotropy.

Tail-like features in spectra may affect experimental analysis.

Abstract

Transition metal sulfide perovskites offer lower band gaps and greater tunability than oxides, along with other desirable properties for applications. Here we explore dimensional reduction as a tuning strategy using the Ruddlesden-Popper phases in the Ba-Zr-S system as a model. The three dimensional perovskite BaZrS$_3$ is a direct band semiconductor, with a band gap of 1.5 eV suitable for solar photovoltaic application. However, the three known members of the Ruddlesden-Popper series, are all indirect gap materials, and additionally have lower fundamental band gaps. This is accompanied in the case of by a band structure that is more favorable for carrier transport for oriented samples. The layered Ruddlesden-Popper compounds, show significantly anisotropic optical properties, as may be expected. The optical spectra show tails at low energy, which may complicate experimental characterization of these materials.