A new multifunctional fluorescent molecule for highly efficient non-doped deep-blue electro-fluorescence with high color-purity and efficient phosphorescent OLEDs

Abstract

High efficiency and high color purity are two key factors for achieving non-doped deep-blue organic light-emitting diodes (OLEDs). Herein, a novel emitter 3,6-di-tert-butyl-9-(4′-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)-[1,1′-biphenyl]-4-yl)-9H-carbazole (DTPCZTZ) with a weak donor–acceptor structure containing carbazole as the donor and triazole as the acceptor was designed and synthesized. Photophysics and theoretical calculation show that it has the hybridized local and charge-transfer (HLCT) state. A subtle introduction of tert-butyl on carbazole combined with twisted 3,4,5-triphenyl-4H-1,2,4-triazole endows the molecule with a highly twisted molecular conformation, and it successfully achieves a deep-blue emission. And the non-doped device based on DTPCZTZ showed a electroluminescence (EL) peak at 424 nm, the Commission Internationale de L'Eclairage (CIE) coordinates of (0.17, 0.06), and the maximum external quantum efficiency (EQE_max) up to 7.6%, and is one of the best non-doped OLEDs with pure organic deep-blue HLCT molecules. Importantly, the application potential of DTPCZTZ in phosphorescent OLEDs (PhOLEDs) is also evaluated based on Ir(PPy)₂(acac) and Ir(MDQ)₂(acac) as the dopants and DTPCZTZ as the host, and high-efficiency green and red PhOLEDs with an EQE_max, maximum power efficiency (PE_max), maximum current efficiency (CE_max), and maximum luminance (L_max) of up to 20.1%, 81.5 lm W⁻¹, 72.6 cd A⁻¹, and 29 595 cd m⁻² and 15.3%, 22.1 lm W⁻¹, 21.1 cd A⁻¹, and 10 526 cd m⁻², respectively, were successfully realized. These results provide a valuable strategy for the design of highly efficient deep-blue emitters and using them as host materials, having significant potential for practical applications.