Excitons in one-dimensional van der Waals materials:Sb2S3nanoribbons

Abstract

Antimony sulphide ${\mathrm{Sb}}_{2}{\mathrm{S}}_{3}$ has emerged as a promising material for a variety of energy applications ranging from solar cells to thermoelectrics and solid-state batteries. The most distinctive feature of ${\mathrm{Sb}}_{2}{\mathrm{S}}_{3}$ is its crystal structure, which consists of parallel 1-nm-wide ribbons held together by weak van der Waals forces. This structure clearly suggests that it should be possible to isolate individual ${\mathrm{Sb}}_{2}{\mathrm{S}}_{3}$ ribbons using micromechanical or liquid-phase exfoliation techniques. However, it is not clear yet how to identify the ribbons postexfoliation using standard optical probes. Using state-of-the-art first-principles calculations based on many-body perturbation theory, here we show that individual ribbons of ${\mathrm{Sb}}_{2}{\mathrm{S}}_{3}$ carry optical signatures clearly distinct from those of bulk ${\mathrm{Sb}}_{2}{\mathrm{S}}_{3}$. In particular, we find a large blueshift of the optical absorption edge (from 1.38 to 2.30 eV) resulting from the interplay between a reduced screening and the formation of bound excitons. In addition, we observe a transition from an indirect band gap to a direct gap, suggesting an enhanced photoluminescence in the green. These unique fingerprints will enable extending the research on van der Waals materials to the case of one-dimensional chalchogenides.