Thermally Induced Self-Assembly of Toroidal Conjugated Small Molecules Enabling High-Performance Deep Blue Quantum
Yaxin Li1,2, Yuhong Wang1,2, Shirong Wang1,2
1School of Chemical Engineering and Technology, Tianjin University, Tianjin, China.
Abstract:
The inferior performance of deep blue quantum dot light-emitting diodes (QLEDs) compared with red and green counterparts is hindering the commercialization of full-color QLED display, since their hole mobility of organic hole transport layer (HTL) is lower than the electron mobility of ZnMgO. Although commonly used p‑type small molecules with ordered packing can enhance hole mobility, strong intermolecular interaction causes HTL inhomogeneity and excimer formation. To address this issue, this study designs and synthesizes three propeller-like molecules, HPB-6tBu, HPB-2Cz, and HPB-6Cz, whose molecular structure suppresses face-to-face stacking while allowing for intramolecular toroidal delocalization. Among them, HPB-6Cz bears superior hole mobility, benefiting from its thermally induced self-assembly, which simultaneously achieves homogeneous HTL morphology and ordered molecular packing. The intermolecular π-π interaction among HOMO-located carbazole groups results in a 6.03-fold enhancement in the hole mobility of HPB-6Cz upon self-assembly. Doping HPB-6Cz into PVK permits ordered packing of PVK and the hole mobility of doped HTL is boosted from 2.21 × 10-5 to 1.55 × 10-3 cm2 V-1 s-1. Resulting QLED (CIEy = 0.036) based on ZnCdS/ZnS QDs achieves an external quantum efficiency (EQE) of 23.24%, which is the state-of-the-art EQE reported to date. Its operational half-lifetime also extends from 4321 to 17795 h at 100 cd m-2.
