“Trade‐Off” Hidden in Condensed State Solvation: Multiradiative Channels Design for Highly Efficient Solution‐Processed Purely Organic Electroluminescence at High Brightness

Abstract

Actualizing highly efficient solution‐processed thermally activated delayed fluorescent (TADF) organic light‐emitting diodes (OLEDs) at high brightness becomes significant to the popularization of purely organic electroluminescence. Herein, a highly soluble emitter benzene‐1,3,5‐triyltris((4‐(9,9‐dimethylacridin‐10(9H)‐yl)phenyl)methanone was developed, yielding high delayed fluorescence rate (kTADF > 105 s−1) ascribed to the multitransition channels and tiny singlet–triplet splitting energy (ΔEST ≈ 32.7 meV). The triplet locally excited state is 0.38 eV above the lowest triplet charge‐transfer state, assuring a solely thermal equilibrium route for reverse intersystem crossing. Condensed state solvation effect unveils a hidden “trade‐off”: the reverse upconversion and triplet concentration quenching processes can be promoted but with a reduced radiative rate from the increased dopant concentration and the more polarized surroundings. Striking a delicate balance, corresponding vacuum‐evaporated and solution‐processed TADF‐OLEDs realized maximum external quantum efficiencies (EQEs) of ≈26% and ≈22% with extremely suppressed efficiency roll‐off. Notably, the wet‐processed one achieves to date the highest EQEs of 20.7%, 18.5%, 17.1%, and 13.6%, among its counterparts at the luminance of 1000, 3000, 5000, and 10 000 cd m−2, respectively.

Utilizing a Spiro TADF Moiety as a Functional Electron Donor in TADF Molecular Design toward Efficient “Multichannel” Reverse Intersystem Crossing

“…Thus, to have a further understanding of their excited states, zero–zero transition energies ( E 0−0 ) of 1 CT and 3 CT were calculated for both compounds (Figure S5, Supporting Information) . Since 3 LE of TADF materials with large twisting angle usually depends on the 3 LE of their isolated D or A unit due to the restricted conjugation, 3 LE energies of both compounds are estimated by the T 1 energy levels of the ACRPh, TRZ, and DMTO units calculated at the TDDFT/B3LYP/6‐31G* level in toluene based on their optimized S 0 geometries . All those data are shown in Tables S4 and S5 in the Supporting Information.…”

Fused tetracyclic tris[1,2,4]triazolo[1,3,5]triazine as a novel rigid electron acceptor for efficient thermally activated delayed fluorescence emitters

“…Metal free thermally activated delayed uorescence (TADF) has attracted substantial attention from the scientic community due to its competence of utilizing both singlet and triplet excitons for light emission. [1][2][3][4][5][6][7] The seminal work of Adachi et al 2 elucidating the up conversion of a triplet exciton into a singlet state via a reverse intersystem crossing (RISC) process by regulating the singlet-triplet splitting energy (DE ST ), provided new prospects in the eld of TADF research, with a bright future in the area of organic light emitting diodes (OLEDs). To realize efficient TADF materials from the quantum theory perspective, the spatial separation of electron densities of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) in one single molecule is needed to acquire a near-zero DE ST ; and consequently to realize an efficient RISC process.…”

“…Recently, a renewed interest for star-shaped emitters (D 3 -A) to be used in OLEDs arises. [5][6][7] In general, star-shaped molecules are of many advantages over their linear analogues as they encompass both the character of small molecules and polymers with well-dened molecular structure, superior chemical purity as well as good solution processability. [8][9][10][11][12][13][14][15] There are several examples of uorene containing star-shaped molecules showing improved device characteristics in comparison to the linear molecules.…”

Efficient Near‐Infrared Emission by Adjusting the Guest–Host Interactions in Thermally Activated Delayed Fluorescence Organic Light‐Emitting Diodes

“…To mitigate the disadvantageous blueshift in NIR TADF devices for better performance beyond 700 nm emission, herein we propose that the molecular dipole moment as another important factor should be carefully considered in selecting host materials. The solid‐state solvation effect would affect not only the luminescence spectra but also the quantum yield by the physical perturbation of molecular states of guests . In demonstrating how important it is to understand the effects of the environment in these D–A emitters for NIR TADF devices, a series of hosts with p/n‐type characteristics and different dipole moments were chosen, and their effects on an NIR TADF emitter APDC‐DTPA were systematically studied.…”