Highly Efficient Blue/Deep‐blue Circularly Polarized Electroluminescence with Small Efficiency Roll‐Offs
Yan Yan, Zhuang Cheng, Yangze Xu, Zihan Su, Yaxue Wang, Xin He, Zujin Zhao, Futong Liu, Ping Lü
Abstract
Abstract Developing efficient blue/deep‐blue circularly polarized organic light‐emitting diodes (CP‐OLEDs) with small efficiency roll‐off remains a great challenge for wide color gamut and high contrast 3D displays. Here, two pairs of chiral stable enantiomers, ( R / S )‐PPI‐OBN‐CN and ( R / S )‐PyI‐OBN‐CN, composed of imidazole derivatives phenanthroimidazole (PPI) and pyrenoimidazole (PyI) donors, and chiral group of ( R / S )‐octahydro‐binaphthol (OBN‐CN) acceptor are designed. These new blue/deep‐blue molecular architectures exhibit excellent thermal and electrochemical stabilities, hybrid local and charge transfer (HLCT) excited state, and clear CPL characteristics with dissymmetry factors (|g PL |) of 1.57 × 10 −3 /2.49 × 10 −3 in the neat films. Moreover, the CP‐OLEDs based on ( R / S )‐PPI‐OBN‐CN and ( R / S )‐PyI‐OBN‐CN exhibit the deep‐blue/pure‐blue emission with the CIE coordinates of (0.15, 0.08) and (0.15, 0.14), the maximum external quantum efficiencies (EQEs) of 7.25% and 8.11% and very small efficiency roll‐offs of 17.6% and 1.8% at the luminescence of 1000 cd m −2 , respectively. Even when the brightness is increased to 10000 cd m −2 , ( R / S )‐PyI‐OBN‐CN‐based device could still maintain as high as 6.68%. Obvious circularly polarized electroluminescence (CPEL) activities with the EL dissymmetry factors ( g EL ) of +1.54 × 10 −3 /−1.63 × 10 −3 and +1.95 × 10 −3 /−1.72 × 10 −3 are also recorded. These are the first highly efficient blue/deep‐blue CP‐OLEDs based on “hot exciton” enantiomers.