Coherent phonon and charge dynamics in antimony sulfide.

Abstract

Antimony Sulfide (Sb2S3) is a promising light absorbing material due to its small bandgap and large absorption coefficient in the visible region. It has recently gained much research interests as a viable material for semiconductor-sensitized solar cells (SSSCs). While there are numerous studies done to optimize the features of the Sb2S3-SSCs, the phonon and charge dynamics are not thoroughly studied. In this work, transient absorption spectroscopy (TAS) will be used to investigate this.

TAS using a 400nm excitation wavelength shows coherent oscillations which were resolved to have a frequency of (1.91±0.01)THz and a small cosine phase of (-0.3±0.3)rad. The oscillations were determined to be from phonon with frequency slightly red-shifted from the AgRaman peaks, which can be attributed to a phonon softening effect. With non-resonant excitation, no oscillations are observed and therefore a displacive excitation can be attributed to the phonon generation in Sb2S3. In addition, TAS revealed two processes that decay within 10ps. One of the processes has a lifetime that resembles the laser temporal width and can be attributed to multi-probe absorption. The other process has a lifetime that decreases with increasing pump fluence and can be attributed to the electron-incoherent phonon scattering. The large scattering processes found may also indicate a possible energy loss channel for the carriers.

These findings thus shed new light on the interesting quasi-particle and charge dynamics in this novel light harvesting system.