Polycrystalline semiconductor films, such as methylammonium lead iodide, cadmium telluride, copper–indium–gallium selenide, etc., are being intensively studied because of their great potential for highly efficient and cost-effective solar cells. Among them, polycrystalline antimony chalcogenide films are also promising for photovoltaic applications because they are nontoxic, stable, and flexible and have a suitable band gap. Considerable effort has already been devoted to improving the power conversion efficiency of antimony chalcogenide solar cells, but their efficiency still lingers below 10% due in part to scarce fundamental optoelectronic studies that help guide their development. Here, we use a combination of time-resolved terahertz and transient absorption spectroscopies to interrogate the optoelectronic behavior of antimony selenide thin films. By combining these two techniques we are able to monitor both free and trapped carrier dynamics and then evaluate their respective diffusion lengths. Our results indicate that trapped carriers remain mobile and can reach charge-collecting interfaces prior to recombination, and therefore, both free and trapped carriers can contribute to the photocurrent of antimony selenide solar cells.

The Auger recombination in bulk semiconductors can quickly depopulate the charge carriers in a nonradiative way, which, fortunately, only has a detrimental impact on optoelectronic device performance under the condition of high carrier density because the restriction arising from concurrent momentum and energy conservation limits the Auger rate. Here, we surprisingly observed enhanced Auger recombination in an α-Fe2O3 single crystal, a wide bandgap semiconductor with low carrier mobility. The Auger process was ascribed to the Coulombically coupled self-trapped excitons (STEs), and the relaxation of momentum conservation due to the strong spatial localization of these STEs should account for the enhancement. The STE-density dependent kinetics suggested that the strong polaronic effect could cause a micro-heterogeneous distribution of STEs in a high-quality bulk single crystal, which also gave rise to the micro-heterogeneous annihilation dynamics, and a stochastic recombination model was developed and successfully described the STE annihilation dynamics.