Recent progress in the chemical design of TADF materials is summarized from the viewpoint of the effects of the position and number of donor and acceptor units.
High-efficiency orange and red thermally activated delayed fluorescent (TADF) organic light-emitting diodes were fabricated based on a pair of isomers 3,6,11-triAC-BPQ and 3,6,12-triAC-BPQ, containing rigid dibenzo[f,h]pyrido[2,3-b]quinoxaline (BPQ) core and three...
Circularly polarized organic light‐emitting diodes (CP‐OLEDs) that enable circularly polarized luminescence (CPL) are promising for 3D display and photonic applications. However, the device efficiency and CPL character of CP‐OLEDs still lag behind the practical requirements. Here, two pairs of axially chiral emitting enantiomers, flexible (R/S)‐ODQPXZ and rigid (R/S)‐ODPPXZ, are reported by fusing (R/S)‐octahydro‐binaphthol chiral source, diphenyl quinoxaline (DQ)/dibenzo[a,c]phenazine (DP) acceptors and phenoxazine (PXZ) donors. The symmetrical chiral‐acceptor‐donor configuration endows them thermally activated delayed fluorescence (TADF) properties with small singlet–triplet energy gaps of 0.16 and 0.07 eV, high photoluminescence quantum yields of 92% and 89% in doped films, and obvious mirror‐image CPL characteristics, respectively. The CP‐OLEDs based on these TADF enantiomers not only show a maximum external quantum efficiency of 28.3% with yellow emission for (R/S)‐ODQPXZ and 20.3% with orange‐red emission for (R/S)‐ODPPXZ, but also display the CPL with dissymmetry factors (gEL) of 6.0 × 10−4 and 2.4 × 10−3, respectively. The high efficiency and obvious CPL of (R)‐ODPPXZ arise from a synergetic interplay of the TADF skeleton and the rigid coplanar acceptor for efficient chiral induction and suppressed intramolecular rotational quenching.
Perovskite light-emitting diodes (PeLEDs) featuring excellent
electroluminescent
(EL) characteristics and facile production have been emerging as promising
candidates for next-generation high-definition displays. In recent
years, tremendous advances have been achieved in the EL efficiency
of PeLEDs. However, their poor operational stability impedes practical
applications. Particularly, the severe spectral instability of pure-blue
and pure-red PeLEDs lags far behind the requirements of commercial
displays. In this Perspective, the critical factors related to device
degradation are first summarized, including perovskite crystal defects,
unbalanced charge injection, Auger recombination, and Joule heating.
Then, the recent progress in improving the operational and spectral
stabilities is reviewed in categories. Considering the present achievements,
we provide potential research directions for further development of
stable PeLEDs.
Compared with green and blue thermally activated delayed fluorescence (TADF), red emitters remain a hot spot in the application of organic light-emitting diodes (OLEDs), which suffer from significant non-radiative decay....
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