Charge carrier dynamics and self-trapping on Sb 2 S 3 ( 100 )

To achieve high power conversion efficiencies in photovoltaic or photoelectrochemical cells, an understanding of the dynamical processes in the electrode materials upon photoexcitation is crucial. Antimony sulfide is a promising candidate material. The authors present time-resolved two-photon photoemission measurements from a Sb${}_{2}$S${}_{3}$(100) single crystal surface. A first laser pulse generates a population of free charge carriers that are probed by a second pulse. Ultrafast relaxation towards the conduction band minimum is followed by a fast decay within 1.3 ps into two longer-lived trap states, self-trapped electrons and self-trapped excitons states, with lifetimes of 27 and 63 ps, respectively. The results support a polaronic self-trapping mechanism by optical phonons.