  Layered indium selenide (InSe) is a van der Waals solid that has emerged as a
promising material for high-performance ultrathin solar cells. The
optoelectronic parameters that are critical to photoconversion efficiencies,
such as hot carrier lifetime and surface recombination velocity, are however
largely unexplored in InSe. Here, these key photophysical properties of layered
InSe are measured with femtosecond transient reflection spectroscopy. The hot
carrier cooling process is found to occur through phonon scattering. The
surface recombination velocity and ambipolar diffusion coefficient are
extracted from fits to the pump energy-dependent transient reflection kinetics
using a free carrier diffusion model. The extracted surface recombination
velocity is approximately an order of magnitude larger than that for
methylammonium lead-iodide perovskites, suggesting that surface recombination
is a principal source of photocarrier loss in InSe. The extracted ambipolar
diffusion coefficient is consistent with previously reported values of InSe
carrier mobility.
