White organic light‐emitting diodes (WOLEDs) have been regarded as the most promising candidate for full‐color display and solid‐state lighting applications owing to their favorable merits of high efficiency, superior white color balance, simple fabrication, and large‐area manufacturing possibility. Particularly, single‐emissive‐layer WOLEDs (SEL‐WOLEDs) with the reduced structural complexity, lower process cost, and feasible solution processing have drawn particular attentions. Numerous strategies have been proposed in recent years to construct SEL‐WOLEDs with improved device performance. This review focuses on the aspects, including: a) the molecular design methods for achieving a single‐molecule WOLED; b) the energy transfer mechanisms in various multiple‐molecule SEL‐WOLEDs with all‐fluorescence, all‐phosphorescence, and fluorescence‐phosphorescence hybrid structures; c) the combination of exciplex emitters and complementary fluorescent/thermally‐activated delayed fluorescent/phosphorescent emitters to realize SEL‐WOLEDs. Some future prospects on new opportunities and technological challenges in SEL‐WOLEDs are also covered.

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.

White organic light-emitting diodes (WOLEDs) using thermally activated delayed fluorescence (TADF)-based single emissive layer (SEL) have attracted enormous attention because of their simple device structure and full exciton utilization potential for high efficiency. However, WOLEDs made of an all-TADF SEL usually exhibit serious efficiency roll-off and poor color stability due to serious exciton-annihilation and unbalanced radiative decays of different TADF emitters. Herein, a new strategy is proposed to manipulate the TADF-sensitized fluorescence process by combining dual-host systems of high triplet energy with a conventional fluorescent emitter of complementary color. The multiple energy-funneling paths are modulated and short-range Dexter energy transfer is largely suppressed due to the steric effect of peripheral tert-butyl group in the blue TADF sensitizer. The resulting all-fluorescent WOLEDs achieve an unprecedentedly high external quantum efficiency of 21.8% with balanced white emission of Commission Internationale de l’Eclairage coordinate of (0.292, 0.343), accompanied with good color stability, reduced efficiency roll-off, and prolonged operational lifetime. These findings demonstrate the validity of this strategy for precisely allocating the exciton harvesting in SEL WOLEDs.

With the wide application of OLEDs in the field of display and lighting, low-cost, large-area OLEDs fabrication technologies are emerging. Among them, printed OLEDs have attracted extensive attentions, and have...