Computing the Effect of Metal Substitution in Metal-Organic Frameworks on the Recombination Times of Charge Carriers

Metal-organic frameworks (MOFs) have been attracting increasing attention in the fields of photoactive applications, for which understanding the factors governing their excited-state properties is critical. One of the major challenges includes reducing the energy losses due to the phonon-assisted nonradiative recombination and extending charge-carrier lifetimes. Metal substitution constitutes a way to modify the electronic structure of MOFs. Among different options, Ce-MOFs are often considered; however, from the theoretical perspective, little is known about the charge-carrier dynamics and recombination pathways in such systems. Therefore, in this work, the electron-hole recombination in a prototype Ce-based MOF is investigated. The limit of a radiative charge-carrier lifetime is estimated theoretically. The nonradiative recombination process is simulated using nonadiabatic molecular dynamics within the decoherence-induced surface-hopping approach and the corresponding electron-hole recombination rates are calculated, demonstrating that the charge-carrier lifetimes in Ce-MOFs are in excellent agreement with the experimental data. Importantly, the vibrational modes, which are the main contributors to the nonradiative decay, are analyzed. In particular, the role of the soft phonon modes in the charge-carrier recombination process is highlighted. Based on this data, the routes for modulating electron-hole lifetimes are suggested.