where h is Plank constant, k is Boltzmann constant, T is temperature, λ is reorganization energy, and J is charge transfer integral between two molecules (Fig. ) . At a given temperature, the electron transfer rate (ket) is determined by J and λ. Since the more compact molecular stacking after deuteration, the charge transfer integral (J) for deuterated exciplexes can be slightly higher and thus achieving better charge transport. Besides, we also analysed the reorganization energy (λ) of those molecules before and after deuteration. As depicted in Fig. , the λ values of electron donors expressively reduced from 0.775 eV for SiCzCz to 0.655 eV for D-SiCzCz, while mildly decreased for electron acceptors from 0.655 eV for SiTrzCz2 to 0.628 eV for D-SiTrzCz2 (Supplementary Fig. and). The discrepancy in the extent of reduction may be attributed to the influence of the site of deuterium substitution. In the case of the donor component, the deuterium substitutions take place on the carbazoles, which are directly implicated in charge transfer, and thus the reduction of reorganization energy for D-SiCzCz is considerable. Conversely, in the acceptor component, the carbazoles are not directly involved in charge transfer, therefore, the alteration in reorganization energy for D-SiTrzCz2 is relatively modest. This also explained why donors showed a more significant enhancement on charge transport than acceptors aforementioned. Overall, an increase in J and a decrease in λ together enhance the charge transport capability of those materials, finally resulting in higher current densities in electron only devices.