Molecular Orientation Effects in Organic Light-Emitting Diodes

It is well known that by horizontally aligning the transition dipole moments of exciton dipoles in the emitter films of organic light-emitting diodes (OLEDs), a larger fraction of the radiative power can escape from the OLED stack, increasing the light outcoupling efficiency by up to 50% compared to the isotropic counterparts. In this account, we review recent advances in understanding this phenomenon, with a special focus on the practical strategies to control the molecular orientation in vacuum-deposited films of thermally activated delayed fluorescent (TADF) dyes. The role of molecular orientation in efficient OLED design is discussed, which has been experimentally proven to increase the external quantum efficiency exceeding 30%. We outline the future challenges and perspectives in this field, including the potential to extend the concept to the solution-processed films. Finally, the development of multiscale computer simulations is reviewed to assess their potential as a complementary approach to systematically screening OLED molecules in silico.