Enhanced Förster Energy Transfer Through Horizontal Orientation of Sensitizer Molecules in Hyperfluorescent Organic Light‐Emitting Diodes

Abstract Förster resonance energy transfer (FRET) in sensitized fluorescent (SF) organic light‐emitting diodes (OLEDs) is an important process for suppressing triplet exciton loss during energy transfer toward the fluorescent dopant. Herein, the contribution of the relative orientation between the sensitizer and emitting dopant to the FRET in state‐of‐the‐art SF OLEDs is explained using experimental and theoretical approaches. The enhanced relative orientation factor (κ²) from 0.375 to 1.250 is theoretically demonstrated in the FRET theory depending on the orientation of the sensitizer and emitting dopant. On comparing two SF OLED systems with different sensitizers, the sensitizer with a higher horizontal dipole orientation exhibits a higher FRET rate, resulting in the enhanced κ². The exciton dynamics under device operation are explored to quantitatively verify the contribution of the enhanced FRET rate to the exciton transfer processes; the triplet consumption rate of the sensitizer improves by 2.2 times, demonstrating an efficient exciton transfer.