Temperature-driven journey of dark excitons to efficient photocatalytic water splitting in β-AsP

Limited availability of photogenerated charge carriers in two-dimensional (2D) materials, due to high exciton binding energies, is a major bottleneck in achieving efficient photocatalytic water splitting (PWS). Strong excitonic effects in 2D materials demand precise attention to electron-electron correlation, electron-hole interaction and electron-phonon coupling simultaneously. In this work, we explore the temperature-dependent electronic and optical responses of an efficient photocatalyst, blue-AsP (β-AsP), by integrating electron-phonon coupling into state-of-the-art GW + BSE calculations. Interestingly, strong electron-lattice interaction at high temperature promotes photocatalytic water splitting with an increasing supply of long-lived dark excitons. This work presents an atypical observation contrary to the general assumption that only bright excitons enhance the PWS due to prominent absorption. Dark excitons, due to the low recombination rate, exhibit long-lived photogenerated electron-hole pairs with high exciton lifetime increasing with temperature up to ∼0.25 μs.