Highly Efficient Utilization of High‐Energy Excitons in Multilayer WSe2 for Self‐Powered Ultraviolet Photodetector With Near‐Unity External Quantum Efficiency

Abstract High‐energy excitons in transition metal dichalcogenides (TMDs), resulting from intrinsic van Hove singularities in the density of states, demonstrate strong ultraviolet light absorption capacity and significant potential for the development of high‐performance ultraviolet photovoltaic devices. Nevertheless, only a limited fraction of carriers from high‐energy excitons can be effectively utilized due to unique parallel band structures and unfavorable recombination processes. To efficiently exploit the high‐energy excitons, a two‐terminal photodetector based on multilayer WSe 2 with a unilateral Schottky junction is designed. Benefiting from the strong built‐in electric field, a superior responsivity of 286 mA W −1 and near‐unity external‐quantum‐efficiency (EQE) of 98% is achieved at 360 nm. Transient absorption spectroscopy demonstrates that the high EQE is attributed to the efficient separation and transfer of high‐energy excitons achieved by the strong built‐in electric field, thus circumventing unfavorable recombination processes and enabling highly efficient utilization of high‐energy excitons. This work provides an effective strategy for constructing high‐performance and low‐power consumption ultraviolet photodetectors.