Band versus Polaron: Charge Transport in Antimony Chalcogenides

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 (X = S, Se). Here we report band-like transport in Sb₂X₃, determined 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 Fröhlich coupling constants (α ≈ 2), large polaron radii (extending over several unit cells), and high carrier mobility (an isotropic average of >10 cm² V^-1 s^-1 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 Sb₂X₃ solar cells is not limited by intrinsic self-trapping.