Properties of the ferroelectric visible light absorbing semiconductors: Sn$_2$P$_2$S$_6$ and Sn$_2$P$_2$Se$_6$

TL;DR

This study uses first principles calculations to analyze ferroelectric semiconductors Sn$_2$P$_2$S$_6$ and Sn$_2$P$_2$Se$_6$, revealing their electronic, optical, and transport properties relevant for photovoltaic applications.

Contribution

It provides detailed electronic and optical property data for these ferroelectric semiconductors, serving as models for understanding ferroelectric photovoltaic effects.

Findings

Indirect band gaps of 2.20 eV and 1.55 eV.

Strong optical absorption above the direct gaps.

Favorable band structures for carrier transport.

Abstract

Ferroelectrics with suitable band gaps have recently attracted attention as candidate solar absorbing materials for photovoltaics. The inversion symmetry breaking may promote the separation of photo-excited carriers and allow voltages higher than the band gap. However, these effects are not fully understood, in part because of a lack of suitable model systems for studying these effects in detail. Here, we report properties of ferroelectric Sn$_2$P$_2$S$_6$ and Sn$_2$P$_2$Se$_6$ using first principles calculations. Results are given for the electronic structure, carrier pocket shapes, optical absorption and transport. We find indirect band gaps of 2.20 eV and 1.55 eV, respectively, and favorable band structures for carrier transport, including both holes and electrons. Strong absorption is found above the direct gaps of 2.43 eV and 1.76 eV. Thus these compounds may serve as useful model systems for understanding photovoltaic effects in ferroelectric semiconductors.