A theoretical analysis on the electron and energy transfer between host and guest materials in phosphor–doped OLED

Phosphor doped OLEDs have been developed all the way in recent years due to their high and stable efficiency and more practical applications in various display devices. However, complicated electron and energy transfer between host and guest materials have not been clear to us so far, which brings about the difficulty in making favorable doping scheme to realize best performance. In order to present some issues for these processes, we carried out density functional theory (DFT) calculations and molecular dynamics (MD) simulation to describe the electron and energy transfer between host molecule CBP and guest molecules (ppy)2Ir(bppo), (bppo)2Ir(ppy) and (bppo)2Ir(acac). The results show that the energy transfer from host to guest molecules is not only more significant than the charge transfer, but also exhibits less dependence on the relative orientation between host and guest molecules. It indicates the decisive contribution of energy transfer to the high-efficiency phosphorescence of guest molecules. At the same time, the much higher energy transfer rates between triplet excited states than those between singlet excited states indicates the importance of generating triplet-state excitons in host materials for phosphor doped OLEDs. Therefore, we hope this work could provide some theoretical guidance for further development of host–guest materials.