High-performance non-doped blue OLEDs based on 1,2,4-triazole-phenanthroimidazole derivatives with negligible efficiency roll-off

Triazole and phenanthroimidazole moieties are commonly used to construct efficient blue-emitting materials as acceptors and donors, respectively. Benefitting from the D–A coupling of the two moieties, two novel bipolar blue emitters, TAZ-PPI and 4NTAZ-PPI, were synthesized. They showed excellent thermal stability and high photoluminescence quantum yields (PLQYs). Non-doped blue organic light-emitting diodes (OLEDs) based on 4NTAZ-PPI and TAZ-PPI present maximum external quantum efficiencies of 7.3% and 5.9%, respectively, and exhibit negligible efficiency roll-off. The CIE coordinates are (0.149, 0.131) and (0.149, 0.130) at a luminance of 1000 cd m−2, respectively. Because the combination of electron donors and acceptors is a favorable method to balance the carrier injection and transport, 4NTAZ-PPI and TAZ-PPI exhibit excellent hole and electron transporting capabilities.