Band Versus Polaron: Charge Transport in Antimony Chalcogenides

TL;DR

This study reveals that charge transport in antimony chalcogenides is band-like with high mobility governed by large polarons, indicating intrinsic limits are not due to self-trapping, which is promising for photovoltaic applications.

Contribution

The paper provides first-principles analysis showing band-like transport and polaron effects in Sb2X3, clarifying charge transport mechanisms relevant for solar cell performance.

Findings

Charge transport in Sb2X3 is band-like with high mobility.

Transport is governed by large polarons with moderate Fröhlich coupling.

Intrinsic mobility is limited by polar phonon scattering, not self-trapping.

Abstract

Antimony sulfide (Sb2S3) and selenide (Sb2Se3) are emerging earth-abundant absorbers for photovoltaic applications. Solar cell performance depends strongly on charge carrier transport properties but these remain poorly understood in Sb2X3. Here we report band-like transport in Sb2X3 by investigating the electron-lattice interaction and theoretical limits of carrier mobility using first-principles density functional theory and Boltzmann transport calculations. We demonstrate that transport in Sb2X3 is governed by large polarons with moderate Fr\"ohlich coupling constants (~ 2), large polaron radii (extending over several unit cells) and high carrier mobility (an isotropic average of > 10 for both electrons and holes). The room temperature mobility is intrinsically limited by scattering from polar phonon modes and is further reduced in highly defective samples. Our study confirms that the performance of the Sb2X3 solar cells is not limited by intrinsic self-trapping.