Formation of Anisotropic Polarons in Antimony Selenide

TL;DR

This study uses advanced pump-probe techniques to observe the formation of anisotropic polarons in Sb2Se3, revealing structural dynamics that influence its optoelectronic properties and carrier trapping mechanisms.

Contribution

It provides direct structural evidence of polaron formation and dynamics in Sb2Se3, a key step in understanding its optoelectronic behavior.

Findings

Opposite separation changes of Se2-Sb2 and Sb2-Sb1 atom pairs within a few picoseconds.

Intermediate structural distortions last several tens of picoseconds and relate to carrier trapping.

Formation of large, anisotropic polarons confirmed by atomic displacement analysis.

Abstract

Antimony Selenide (Sb$_2$Se$_3$) is an attractive candidate of photovoltaics with not yet satisfying efficiency. Beside defects, polaron formation originated from lattice distortion was proposed to account for trapping free carriers, and the subsequent photoexcitation dynamics and optoelectronic properties, but such a mechanism is still lack of structural observations. Here we directly track the pathways of carrier and lattice evolutions after photoexcitation through optical and electron diffraction pump-probe methods, revealing the temporal correlations between dynamics of both degrees of freedom. The observed opposite separation changes of Se2-Sb2 and Sb2-Sb1 atom pairs in a few picoseconds, and the intermediate state induced by local structural distortions lasting several tens of picoseconds, coinciding with the optical phonons population and coupling, and the trapping process of carriers, respectively, together with the analyses of modulation on diffuse scattering by the atomic displacement fields of polaron model, indicate the formation of anisotropic polarons with large size. Our findings provide carrier and structural information for helping the elucidation of polaron scenario in Sb2Se3, and probably in materials with anisotropic structure and soft lattice which are popular in developing novel optoelectronics.