Unraveling the Fate of Host Excitons in Host–Guest Phosphorescent Organic Light-Emitting Diodes

Abstract

Understanding the energy- and charge-transfer mechanisms in host-guest systems is crucial for improving the performance of organic light-emitting diodes (OLEDs), but it presents a theoretical challenge because of the disordered molecular environment. Here, we address the fate of excitons that form on the host in a 2,8-bis(triphenylsilyl)dibenzofuran-Ir(ppy)3 phosphorescent OLED through a quantum mechanics/molecular mechanics simulation. Our results demonstrate that triplet host excitons can be harvested through efficient energy transfer to the T1 state of the guest allowed by an excellent spectral overlap. A detailed analysis of the guest absorption spectrum uncovers the fact that high-lying guest singlet states play a critical role in utilizing singlet host excitons. Furthermore, we investigate the process where host excitons break up and re-form on the guest and show it is unfavored owing to the high energy barrier. This work thus reveals that energy transfer is the primary quenching mechanism for host excitons and highlights the strategies for a better host-guest design.