Ultrafast self-trapping of photoexcited carriers sets the upper limit on antimony trisulfide photovoltaic devices

Abstract

Antimony trisulfide (Sb₂S₃) is considered to be a promising photovoltaic material; however, the performance is yet to be satisfactory. Poor power conversion efficiency and large open circuit voltage loss have been usually ascribed to interface and bulk extrinsic defects By performing a spectroscopy study on Sb₂S₃ polycrystalline films and single crystal, we show commonly existed characteristics including redshifted photoluminescence with 0.6 eV Stokes shift, and a few picosecond carrier trapping without saturation at carrier density as high as approximately 10²⁰ cm⁻³. These features, together with polarized trap emission from Sb₂S₃ single crystal, strongly suggest that photoexcited carriers in Sb₂S₃ are intrinsically self-trapped by lattice deformation, instead of by extrinsic defects. The proposed self-trapping explains spectroscopic results and rationalizes the large open circuit voltage loss and near-unity carrier collection efficiency in Sb₂S₃ thin film solar cells. Self-trapping sets the upper limit on maximum open circuit voltage (approximately 0.8 V) and thus power conversion efficiency (approximately 16 %) for Sb₂S₃ solar cells.