EQE Climbing Over 6% at High Brightness of 14350 cd/m² in Deep-Blue OLEDs Based on Hybridized Local and Charge-Transfer Fluorescence

Abstract

Three deep-blue emitters PPi-Pid, PPi-Xid, and PPi-Mid based on a novel conjugated system phenantroimidazole-π-indolizine have been designed and synthesized. Here, indolizine with appropriate π-conjugation length was used as the acceptor profited from its high-photoluminescence quantum yield and good electron-withdrawing ability. Fluorescent organic light-emitting diodes (OLEDs) based on PPi-Pid, PPi-Xid, and PPi-Mid achieved deep-blue emissions with the Commission Internationale de L'Eclairage coordinates of (0.151, 0.076), (0.155, 0.052), and (0.153, 0.052); high brightness of 14350, 4377, and 4002 cd/m; and high external quantum efficiencies (EQEs) of 6.01, 3.90, and 4.28%, respectively. Moreover, it is noticeable that all of the devices exhibited efficiencies increasing with brightness. In particular, the PPi-Pid-based device exhibited high EQE over 6% at a high brightness of 14350 cd/m. Such high brightness along with high EQE is very rare whether in deep-blue fluorescent or thermally activated delayed fluorescent OLEDs.

Imidazole derivatives for efficient organic light-emitting diodes

“…maintained at 3.01%). The three deep-blue emitters PPi-Pid, PPi-Xid, and PPi-Mid based on the novel conjugated system phenantroimidazole-π-indolizine were reported by Zhang [58]. Indolizine, with an appropriate π -conjugation length, was used as the acceptor due to its high PLQY and good electron-withdrawing ability.…”

Imidazo[1,2‐a]pyridine as an Electron Acceptor to Construct High‐Performance Deep‐Blue Organic Light‐Emitting Diodes with Negligible Efficiency Roll‐Off

“…However,mosto fthem would internally generate intramolecular charge transfer (ICT), leading to energyc onsumption and the redshift of emission. [18] Recently, Su et al reported as eries of new fluorescent emitters, one of which realized an EQE of 4.22 %a t1 0000 cd m À2 .H owever,t he CIE coordinates of (0.145, 0.104) did not meet the NTSC requirements. [19] Lu et al reported deep-blue fluorescent OLEDs based on anthracened erivatives, which possessed an EQE of 3.21 %a t1 0000 cd m À2 with CIE coordinates of (0.15, 0.07).…”

“…We have developedb lue electroluminescent materials with the IP isomer. [18] Moreover,t he frontier molecular orbitals( FMOs) and energy levels of IP,T P, and BI are shown in Figure 1. In practice, [1,2,4]triazolo[1,5-a]pyridine( TP) and 1 H-benzo[d]imidazole (BI) have been employed to construct deep-blue light-emitting materials [26][27][28] owing to their lowest unoccupied molecular orbital (LUMO) levels, which are essential to determinetheir electron-withdrawing ability;s tronger electron-withdrawing ability depends on ad eeper LUMO level.…”

Donor and Acceptor Fused 16,16‐Dimethyl‐11,16‐dihydrodibenzo[2,3:5,6]pyrrolizino[1,7‐ab]acridine as a Blue‐Emitting Chromophore for High External Quantum Efficiency and Long Lifetime

“…The external quantum efficiency (EQE) of D‐A type or D‐π‐A type blue fluorescent emitters was generally below 5% due to spin statistics limitation [ 23 ] and the blue emitters with above 5% EQE were mainly limited to pyrene or imidazole type materials. [ 24–31 ] Besides, the full width at half maximum (FWHM) was above 50 nm [ 31–35 ] and only very few emitters showed FWHM below 40 nm. [ 24 ] However, the D‐A and D‐π‐A type emitters also suffered from color purity due to intramolecular charge transfer (ICT) as it resulted in red‐shifted emission with broad spectrum.…”