Nonradiative Relaxation of Photoexcited Black Phosphorus Is Reduced by Stacking with MoS2: A Time Domain ab Initio Study

Black phosphorus (BP) is an appealing material for applications in electronics and optoelectronics because of its tunable direct band gap and high charge carrier mobility. For real optoelectronic device utilization, nonradiative electron-hole recombination should be slow because it constitutes a major pathway for charge and energy losses. Using time-domain density functional theory combined with nonadiabatic (NA) molecular dynamics, we show that nonradiative electron-hole recombination occurs within several tens of picoseconds in bilayer BP, agreeing well with experimental data. When a single layer of BP is stacked with monolayer MoS2, the recombination is reduced because of the increased band gap and reduced electron-phonon NA coupling compared to bilayer BP. The slow electron-phonon energy losses in BP-MoS2 van der Waals heterojunction relative to bilayer BP indicate that rationally stacking BP with other two-dimensional materials is an attractive route for designing novel and efficient photovoltaic materials.