Direct measurement of coherent phonon dynamics in solution-processed stibnite thin films

We report observations of coherent phonon oscillations in solution-processed polycrystalline stibnite $({\mathrm{Sb}}_{2}$${\mathrm{S}}_{3})$ photovoltaic thin films using transient absorption spectroscopy. Detailed optical spectroscopy correlated by extensive first-principles lattice dynamics calculations indicates that the coherent ${B}_{3g}$ longitudinal optical phonon mode with a frequency of 63.74 \ifmmode\pm\else\textpm\fi{} 0.05 ${\mathrm{cm}}^{\ensuremath{-}1}$ (or 1.911 \ifmmode\pm\else\textpm\fi{} 0.002 THz) at room temperature is generated via the impulsive stimulated-Raman-scattering mechanism. These strong electron-phonon interactions indicate a dominant energy-loss channel in these materials that could impose a fundamental limit on their solar energy conversion efficiency.