Synergetic Horizontal Dipole Orientation Induction for Highly Efficient and Spectral Stable Thermally Activated Delayed Fluorescence White Organic Light-Emitting Diodes

Radiative exciton generation and light out-coupling are two crucial factors for highly efficient organic light-emitting diodes (OLEDs). Herein, a thermally activated delayed fluorescence (TADF) material DspiroS-TRZ with high horizontal dipole ratio (HDR, Theta(//) = 82%) is utilized as the blue emitter as well as the host for an orange-red TADF emitter TPA-AQ to fabricate white OLEDs. A synergetic horizontal dipole orientation induction on the transition dipole moment of TPA-AQ is achieved by the highly orientated DspiroS-TRZ, resulting in high HDR (Theta(//) = 96%) of the orange-red emitter. Owing to the simultaneous efficient triplet exciton utilization and highly orientated binary system, a maximum external quantum efficiency (EQE(max)) of 29.3% is achieved for single emission layer (EML) white OLED, with an excellent white light out-coupling efficiency of 34%. In addition, the carrier recombination in the EML is further regulated by inserting an exciton regulation emission layer, which can relieve the trapping effect of the orange-red emitter and guarantee stable Langevin recombination and energy transfer processes for improved electroluminescence spectral stability. An EQE(max) of 31.2% is ultimately achieved for the double-EML white OLED, highlighting the key role of horizontal dipole orientation induction and carrier recombination modulation for highly efficient and spectral stable white OLEDs.

Automated summary

The study utilized a TADF material with high horizontal dipole ratio to fabricate highly efficient white OLEDs. By adjusting the orientation of the emitters and carrier recombination, high quantum efficiency and spectral stability were achieved.