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

Abstract

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, Θ // = 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 (Θ // = 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.

Constructing high-efficiency orange-red thermally activated delayed fluorescence emitters by three-dimension molecular engineering

“…Solution-processable organic light-emitting diodes exhibit a maximum external quantum efficiency of 24.74%. This study provides a universal strategy for designing highperformance TADF emitters through molecular packing and excited state regulation.With a theoretical internal quantum efficiency (IQE) of 100%, thermally activated delayed fluorescence (TADF) materials without noble heavy metals are considered the next-generation emitting materials for organic light-emitting diodes (OLEDs) [1][2][3][4][5][6] . Characterized by the reverse intersystem crossing (RISC) process from triplet state (T 1 ) to singlet state (S 1 ), TADF emitters can thus achieve high-performance OLEDs.…”

“…With a theoretical internal quantum efficiency (IQE) of 100%, thermally activated delayed fluorescence (TADF) materials without noble heavy metals are considered the next-generation emitting materials for organic light-emitting diodes (OLEDs) [1][2][3][4][5][6] . Characterized by the reverse intersystem crossing (RISC) process from triplet state (T 1 ) to singlet state (S 1 ), TADF emitters can thus achieve high-performance OLEDs.…”

Ultra-fast triplet-triplet-annihilation-mediated high-lying reverse intersystem crossing triggered by participation of nπ*-featured excited states

“…Since the EQE max datum of an OLED correlates not only with the PLQY of the emitting layer and the electron-hole balance ratio (γ e-h ), but also with the EUE and the light out-coupling efficiency (η out ) (EQE = γ e-h × φ PL × EUE × η out ) 14 , to gain insight into the reasons for the lower EQE max of Device A than Device B, firstly, horizontal dipole measurements together with optical simulation were carried on CzNI and TPANI [34][35][36] . The results indicated that the neat film samples of CzNI and TPANI showed nearly identical horizontal dipole ratios (Θ // , 86% vs. 85%, vide Fig.…”

Rational design of orange-red iridium(iii) complexes by an isomer engineering strategy for improved performance of white organic light-emitting diodes

“…Research on the development of white organic light-emitting diodes (WOLEDs) is flourishing owing to their great potential in environmentally friendly and energy-saving solid-state lighting technology. [1][2][3][4][5][6][7][8] WOLEDs constructed using complementary colors can obtain stable electroluminescence (EL) spectra along with a relatively simple device configuration and fabrication process. For the realization of high-performance WOLEDs, efficient orange-red emission is an essential component, [9][10][11] however, the exploration of such materials is particularly imperative and remains challenging due to the intrinsic poor emission caused by the energy gap law and the concentration quenching effect in the solid-state.…”