Roles of Molecular Spatial Arrangement in Exciton Energy Transfer in Organic Light-Emitting Diodes: A Theoretical Study

Revealing the mechanism of exciton energy transfer (EET) in the emitting layer (EML) of organic light-emitting devices is significant for improving the device performance. In this paper, we explore how the host-TADF combinations influence EET in the amorphous film, especially for the Dexter energy transfer (DET) process. With the help of density functional theory calculations and molecular dynamics simulations, we study the Förster resonance energy transfer and the DET of two thin films (2,6-2CzBN:4tCzBN and 3,5-2CzBN:4tCzBN) to determine how the intermolecular interaction influences the energy transfer. We find that the exciton coupling value is the decisive factor that leads to the external quantum efficiency difference between the two amorphous films by analyzing the variable in Marcus theory. The molecular spatial arrangement in 3,5-2CzBN is beneficial to enhance exciton coupling. The more space around benzonitriles helps to strengthen fragment interaction between benzonitriles, which plays a vital role in exciton coupling and spatial distribution. This work reveals how the molecular spatial arrangement and interaction influence energy transfer.