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

Authors：Peng, Xiaomei; Qiu, Weidong; Li, Wenqi; Li, Mengke; Xie, Wentao; Li, Wei; Lin, Jianying; Yang, Jiaji; Li, Xin; Su, Shi-jian^*

Source：Advanced Functional Materials, 2022, 32(28): 2203022.

DOI：10.1002/adfm.202203022

• exciton distribution
• light out-coupling
• thermally activated delayed fluorescence
• transition dipole orientation
• 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.