Management of Host–Guest Triplet Exciton Distribution for Stable, High‐Efficiency, Low Roll‐Off Solution‐Processed Blue Organic Light‐Emitting Diodes by Employing Triplet‐Energy‐Mediated Hosts

Abstract

High‐quality hosts are indispensable for simultaneously realizing stable, high efficiency, and low roll‐off blue solution‐processed organic light‐emitting diodes (OLEDs). Herein, three solution processable bipolar hosts with successively reduced triplet energies approaching the T1 state of thermally activated delayed fluorescence (TADF) emitter are developed and evaluated for high‐performance blue OLED devices. The smaller T1 energy gap between host and guest allows the quenching of long‐lived triplet excitons to reduce exciton concentration inside the device, and thus suppresses singlet‐triplet and triplet‐triplet annihilations. Triplet‐energy‐mediated hosts with high enough T1 and better charge balance in device facilitate high exciton utilization efficiency and uniform triplet exciton distribution among host and TADF guest. Benefited from these synergetic factors, a high maximum external quantum efficiency (EQEmax) of 20.8%, long operational lifetime (T50 of 398.3 h @ 500 cd m−2), and negligible efficiency roll‐off (EQE of 20.1% @ 1000 cd m−2) are achieved for bluish‐green TADF OLEDs. Additionally introducing a narrowband emission multiple‐resonance TADF material as terminal emitter to accelerate exciton dynamic and improve exciton utilization, a higher EQEmax of 23.1%, suppressed roll‐off and extended lifetime of 456.3 h are achieved for the sky‐blue sensitized OLEDs at the same brightness.

Carbazole‐Decorated Organoboron Emitters with Low‐Lying HOMO Levels for Solution‐Processed Narrowband Blue Hyperfluorescence OLED Devices

“…Comparison of the maximum EQE of the solution-processed MR-TADF OLEDs reported in the literature. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] Angewandte Chemie safely demonstrate that the performance improvement of Cz-DABNA and t-BuCz-DABNA hyperfluorescence devices is mainly due to the suppression of hole traps by energy level regulation.…”

“…[20][21][22] Compared with evaporation, solution-processing methods have been intensively demonstrated as more economical approaches for the mass production of large-area OLED displays. [23][24][25] However, the efficiency of reported solutionprocessed MR-TADF OLEDs remains far inferior to that of their vacuum-deposited counterparts, [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] among which pure blue devices with y color coordinate below 0.20 show extremely low efficiency with EQE of only 16.6 %. [29] The hyperfluorescence is formed by adding a conventional TADF material with high reverse intersystem crossing (RISC) rate in the emissive layer as the sensitizer, which could obviously improve the efficiency of MR-TADF devices by accelerating the triplet exciton upconversion for avoiding exciton annihilation events of long-lived triplets, [29,33,44,45] such as triplet-triplet and triplet-polaron interactions.…”

“…Compared with evaporation, solution‐processing methods have been intensively demonstrated as more economical approaches for the mass production of large‐area OLED displays [23–25] . However, the efficiency of reported solution‐processed MR‐TADF OLEDs remains far inferior to that of their vacuum‐deposited counterparts, [26–43] among which pure blue devices with y color coordinate below 0.20 show extremely low efficiency with EQE of only 16.6 % [29] …”

Recent advances in the design of afterglow materials: mechanisms, structural regulation strategies and applications

“…77–79 Typically, a TADF chromophore consists of the individual electron acceptor (A) and electron donor (D) fragments. 80,81 A small energy gap Δ E (S1–T1) between T 1 and S 1 is required to achieve efficient RISC at room temperature (Δ E (S1–T1) < 0.2 eV). 82–84 A general strategy to obtain a small Δ E (S1–T1) in pure organic systems is through a twisting intramolecular charge transfer (TICT) strategy, requiring the design of organic TADF molecules with different D and A fragments, thereby reducing the overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO).…”

Trap-regulated highly efficient mechanoluminescence and persistent mechanoluminescence of Ca2MgSi2O7:Eu2+

“…1–10 Mechanoluminescence (ML) is a fascinating phenomenon in which materials can produce light if subjected to mechanical stimuli, such as fracture, friction, compression, grinding, or stretching. 11–14 With their unique ability to directly convert mechanical energy into light energy, mechanoluminescent materials show widespread applications in stress sensors, smart displays, advanced anti-counterfeiting, crack detectors, and intelligent wearable devices. 15–26 During recent years, increasing numbers of mechanoluminescent materials with excellent performance have been developed, such as ZnS:Cu, ZnS:Mn 2+ , 27 CaZnOS:Mn 2+ , 28 and SrAl 2 O 4 :Eu 2+ .…”