Photoexcited charge carrier dynamics in Sb2Se3(100)

Antimony selenide (${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$) consists of one-dimensional ribbons that are van der Waals bonded to each other. Due to its favorable optoelectronic properties, it is a promising material for solar energy conversion. Owing to its narrow direct band gap and its high absorption coefficient it is an efficient absorber for solar light. Besides, it is cheap, stable in harsh environments, and abundant with low toxicity. For its use in solar devices, efficient transport of photoexcited charge carriers towards the active interface and long lifetimes at sufficiently high energies are mandatory. Here time-resolved two-photon photoemission experiments on the (100) surface of ${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$ are presented. Data were taken along and perpendicular to the direction of the one-dimensional ribbons in order to unravel the anisotropic lifetimes and relaxation dynamics of photoexcited charge carriers. In both cases, various conduction bands could be populated and within the first picosecond ultrafast scattering towards the lowest conduction band was observed. Moreover, long lifetimes of up to 35 ps in the conduction band bottom at the surface were obtained and no sign of trapping in defect states was found. These measurements shed light on the relaxation and scattering of free carriers in ${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$, which is the key for the design of ${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$-based electrodes.