MoSe₂/C₆₀ heterojunction may be efficient for photovoltaic applications: time-domain ab initio analysis of interfacial charge separation and recombination dynamics

Transition metal dichalcogenide-fullerene (TMD/fullerene) van der Waals (vdW) heterojunctions are promising for photovoltaic applications due to the intriguing optoelectronic properties of their individual components. However, the fundamental understanding of the photophysical process, especially excited-state charge transfer and recombination, remains insufficient. Here, using ab initio nonadiabatic molecular dynamics, we investigated the photoexcitation dynamics across the interface composed of the MoSe2 monolayer and C-60 molecules and compared it with the WSe2/C-60 heterojunction which has been experimentally demonstrated to be efficient for photovoltaic application. Our simulation results show that MoSe2/C-60 exhibits significantly faster electron transfer and a comparable charge recombination time to WSe2/C-60, demonstrating the more efficient charge separation in the MoSe2/C-60 heterojunction. The difference of electron transfer can be primarily explained in terms of the beneficial energy alignment and the enhanced electron-vibrational interaction. The electron-phonon coupling is stronger for the MoSe2/C-60 heterojunction because the thermal structural fluctuation is stronger due to the presence of lighter Mo and because the donor-acceptor overlap is larger arising from the smaller fluctuation of the interlayer distance. We further showed that the electron transfer in the MoSe2/C-60 heterojunction is several orders of magnitude faster than nonradiative charge recombination. The slow charge recombination is a result of the sufficiently large energy gap and the significantly reduced nonadiabatic couplings. Rapid charge transfer and slow charge recombination ensure that the MoSe2/C-60 heterostructure is an excellent candidate for applications in photovoltaics. Our atomistic investigation provides valuable insights into the photoexcitation dynamics across the interface formed by MoSe2 and C-60, demonstrating the potential of the two components in optimizing the charge separation, which is highly relevant for photovoltaic and optoelectronic applications.