Efficient greenish-blue thermally activated delayed fluorescence Zn complex for organic light emitting devices

Abstract

A greenish-blue zinc complex Zn(PhOBz)-PXZ with enhanced thermally activated delayed fluorescence (TADF) properties has been prepared from Zn(OAc)(2) and 4PXZ2OHBz, a 2-(1H-benzimidazol-2-yl)phenol-based TADF ligand. The TADF phenomenon has been confirmed by time-resolved photoluminescence (TrPL) studies. The DFT calculations show spatially well-separated HOMO and LUMO in their ground states, along with a small energy splitting between the excited singlet (S-1) and triplet (T-1) states, in a good agreement with the TADF mechanism. Due to the high thermal stability of Zn(PhOBz)-PXZ, OLED devices can be fabricated by vacuum vapor deposition, and greenish-blue OLEDs with the maximum emission at 521 nm were successfully demonstrated. The maximum external quantum efficiency (EQE(max)) of 10.6 %, with Commission Internationale de l'Eclairage (CIE) coordinates of (0.28, 0.47) were recorded. Zinc TADF complexes have the advantages of cost-effectiveness, greater abundance of natural resources, environmentally friendly metals, making them potential replacements for future precious metal emitters.