Hot Carrier and Surface Recombination Dynamics in Layered InSe Crystals

TL;DR

This study investigates the hot carrier dynamics and surface recombination in layered InSe crystals, revealing rapid carrier cooling via phonons and high surface recombination velocities, which impact their potential in ultrathin solar cells.

Contribution

It provides the first detailed measurements of hot carrier lifetime and surface recombination velocity in layered InSe using femtosecond transient reflection spectroscopy.

Findings

Hot carrier cooling occurs through phonon scattering.

Surface recombination velocity is significantly higher than in perovskites.

Ambipolar diffusion coefficient aligns with known carrier mobility values.

Abstract

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.