Band versus Polaron: Charge Transport in Antimony Chalcogenides.

Antimony sulfide (Sb 2 S 3 ) and selenide (Sb 2 Se 3 ) are emerging earth-abundant absorbers for photovoltaic applications. Solar cell performance depends strongly on charge-carrier transport properties, but these remain poorly understood in Sb 2 X 3 (X = S, Se). Here we report band-like transport in Sb 2 X 3 , 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 Sb 2 X 3 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 cm 2 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 Sb 2 X 3 solar cells is not limited by intrinsic self-trapping.