Systematic Control of Photophysical Properties of Host Materials for High Quantum Efficiency above 25% in Green Thermally Activated Delayed Fluorescent Devices

Abstract

Three donor-acceptor type host materials with different photophysical properties were developed by managing the interconnect position of the donor and acceptor moieties and molecular structure of the host materials was correlated with the electro-optical properties and device performances of the host materials. The linkage via the meta-position of aromatic units was better than the linkage via ortho- or para-positions and high quantum efficiency of 26.0% in the green thermally activated delayed fluorescent device was achieved using the host material with the meta-linkage.

Chemical and conformational control of the energy gaps involved in the thermally activated delayed fluorescence mechanism

“…Following this idea, the first TADF-based OLED without heavy-metals was reported in 2012 9 . Since then, the TADF mechanism has attracted considerable interest, mainly in the electroluminescence field, leading to OLEDs with high performance [10][11][12][13] , promising a revolution in the smartphone and flat panel displays industry.…”

Recent progress of green thermally activated delayed fluorescent emitters

“…A high PLQY of above 90% and a relatively short excited-state lifetime of 5.1 μs for delayed emission were reported using the 4CzIPN emitter. After the demonstration of a high EQE close to 20% using the organic 4CzIPN TADF emitter for the first time, several works optimizing the device structure of the 4CzIPN TADF OLEDs followed and reported an improved EQE surpassing the EQE obtained by Adachi et al Several bipolar host materials with a triplet energy high enough for both the singlet and triplet harvesting of 4CzIPN were proven to be better than the carbazoletype host materials and provided EQEs higher than 20% [8][9][10][11][12][13][14][15][16][17]. In particular, 3-(3-(carbazole-9-yl)phenyl) pyrido [3 ,2 :4,5]furo [2,3-b]pyridine (3CzPFP) was the best host material of 4CzIPN and realized the best EQE of 31.2% in the 4CzIPN devices [6].…”

Red/NIR Thermally Activated Delayed Fluorescence from Aza‐BODIPYs

“…Over the last few years, an intense researche ffort has been focused on the design and synthesis of thermally activated delayed fluorescence (TADF) materials [1][2][3][4][5] liable of converting the excited T 1 states to emissive S 1 states by absorbing environmental thermal energy through an efficient reverse intersystem crossing( RISC). [6] Although aw ealth of highly efficient blue [7][8][9] green, [10][11][12] yellow [13,14] and orange [15,16] TADF emitters are presently available, the progress on achieving long-lived fluorophores emitting in the deep red part of the visible spectrum has unfortunately been slowed because it requires the optimization of contrasting properties [17][18][19][20] The improved understanding of the processes ruling the effectiveness of RISC process has already revealed some basic design principles on develop-ing highly-effective red TADF emitters [21][22][23][24] In this regard, the most effectives trategy entails the synthesis of dyads with strong, rigid, chemically stable and sterically hindered donor and acceptorm oieties spaceda part and twisted from each other through p-linker units [25][26][27][28][29][30][31] These integrated molecular platformsf ulfil the photophysical and electronic key requirementst oe nhance TADF process, such as:1 )low singlet-triplet energyg ap;2 )ane lectronic coupling betweend onor and acceptorn either too strong nor too weak to enableboth forward and reverse ISC processes; [28] 3) al arge fluorescence rate constant;a nd 4) ah igh chemical, photochemical, and photophysical stabilityo ft he molecular building blocks.…”