Versatile Indolocarbazole‐Isomer Derivatives as Highly Emissive Emitters and Ideal Hosts for Thermally Activated Delayed Fluorescent OLEDs with Alleviated Efficiency Roll‐Off

Abstract

Maintaining high efficiency at high brightness levels is an exigent challenge for real-world applications of thermally activated delayed fluorescent organic light-emitting diodes (TADF-OLEDs). Here, versatile indolocarbazole-isomer derivatives are developed as highly emissive emitters and ideal hosts for TADF-OLEDs to alleviate efficiency roll-off. It is observed that photophysical and electronic properties of these compounds can be well modulated by varying the indolocarbazole isomers. A photoluminescence quantum yield (η ) approaching unity and a maximum external quantum efficiency (EQE ) of 25.1% are obtained for the emitter with indolo[3,2-a]carbazolyl subunit. Remarkably, record-high EQE/power efficiency of 26.2%/69.7 lm W at the brightness level of 5000 cd m with a voltage of only 3.74 V are also obtained using the same isomer as the host in a green TADF-OLED. It is evident that TADF hosts with high η values, fast reverse intersystem crossing processes, and balanced charge transport properties may open the path toward roll-off-free TADF-OLEDs.

Multi‐Resonance Induced Thermally Activated Delayed Fluorophores for Narrowband Green OLEDs

“…Delayed lifetimes ( τ DF s) of 25.9 μs, 16.7 μs, and 19.0 μs for 2F‐BN, 3F‐BN, and 4F‐BN were observed, significantly which are shorter than that of DABNA‐1 ( τ DF =93.7 μs) and TBN‐TPA ( τ DF =51.02 μs), benefiting from the relatively smaller Δ E ST values. Furthermore, the radiative decay rate constants of fluorescent ( k F ), intersystem crossing ( k ISC ), and reverse intersystem crossing ( k RISC ) are estimated from the PLQYs and the lifetimes of the prompt and delayed components (Table ) . Benefiting from the multi‐resonance effect in highly rigid planar structure, the k F values of these MR‐TADF emitters are in the range of 10 7 s −1 , which are much higher than most of the reported TADF emitters …”

High Performance Thermally Activated Delayed Fluorescence Sensitized Organic Light‐Emitting Diodes

“…R D 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 Recently, our group further modified DMIC-TRZ and designed three new TADF materials namely 11-(4-(4,6-Diphenyl-1,3,5-triazin-2-yl)phenyl)-12-phenyl-11,12-dihydroindolo[2,3-a]carbazole (23aICTRZ), 5-(4-(4,6-Diphenyl-1,3,5-triazin-2-yl)phenyl)-7-phenyl-5,7-dihydroindolo[2,3-b] carbazole (23bICTRZ) and 12-(4-(4,6-Diphenyl-1,3,5-triazin-2-yl)phenyl)-5-phenyl-5,12-dihydroindolo[3,2-a] carbazole (32aICTRZ) with indolocarbazoles (ICs) as donor fragments (Figure 13). [39] All of three materials possess excellent PLQYs, efficient TADF character and balanced charge transmission,. They were further testified as hosts for a highly efficient TADF material 9-[4-(4,6-diphenyl-1,3,5triazin-2-yl)phenyl]-N,N,N',N'-tetraphenyl-9H-carbazole-3,6-diamine (DACT-II).…”

“…[35][36][37][38] Indolocarbazoles are good building blocks for TADF materials as they show high hole-transporting ability, high morphological stability and high thermal stability because of their planar and rigid conjugation structures. [39] Besides, they are rich in isomers. Furthermore, due to large steric hindrance, TADF materials based on them usually show low HOMO-LUMO overlap which will result in small DE ST and fast RISC.…”

CN‐Modified Imidazopyridine as a New Electron Accepting Unit of Thermally Activated Delayed Fluorescent Emitters

“…Thermally activated delayedf luorescence( TADF) organicl ightemitting diodes (OLEDs) have recently emerged as an efficient triplet harvesting device to compete with or replace conventional fluorescenta nd phosphorescent OLEDs owing to their ability to exhibit 100 %i nternal quantume fficiency.T hey are similar to phosphorescent OLEDs in terms of efficiency and have advantages in that they can be built from easily available organic materials rather than the expensive noble metals used in phosphorescent OLEDs. [1][2][3][4][5][6][7][8][9][10] However, there are still some challenges limiting their practical applicationss uch as short device lifetime, long delayedf luorescencel ifetime, broade mission spectra,a nd so on. To date, al ot of TADF emitters have been explored, but only af ew can truly demonstrateh igh external quantum efficiency (EQE) and excellents tability for OLEDs.…”