Phenanthrene-based deep-blue fluorophores with balanced carrier transport ability for high-performance OLEDs with a CIEy < 0.04

Abstract

The exploitation of deep-blue emitters with excellent thermal stability, improved color purity and high efficiency is still of great significance for the commercialization of full-color OLEDs. As one of the common functional groups in organic dyes, the phenanthrene moiety possesses blue fluorescence, good carrier transport and a high energy bandgap (E_g), which ensure its potential application in the organic electroluminescence field. In this work, three novel deep-blue fluorophores Cz1, Cz2 and TPA1 with a phenanthrene core and various electron-rich groups were designed and synthesized. The twisted molecular conformation and weak intermolecular charge transfer (ICT) of these tailor-made luminogens endow them with pure deep-blue emission in the range of 414–430 nm with full width at half maximum (FWHM) in the range of 50–61 nm. In addition, all materials exhibit admirable thermal stability with a decomposition temperature (5% weight loss temperature, T_d) above 430 °C and high photoluminescence quantum yields (PLQYs) of 34.5%, 27.1% and 91.1%, respectively, as well as considerable hole and electron transport ability. Non-doped devices B1, B2 and B3 adopting Cz1, Cz2 and TPA1 as emitters show deep-blue emission with Commission Internationale de l’Eclairage (CIE) coordinates of (0.161, 0.035), (0.161, 0.031) and (0.156, 0.037), respectively. In particular, device B3 demonstrates superior electroluminescence (EL) performance with the maximum current efficiency (CE_max), the maximum power efficiency (PE_max) and the maximum external quantum efficiency (EQE_max) of 1.44 cd A⁻¹, 1.03 lm W⁻¹ and 4.36%, respectively. Such a high EQE_max value along with a CIE_y value of 0.037 is rather rare in deep-blue fluorescent OLEDs. Besides, Cz1, Cz2 and TPA1 were also employed as hosts for Ir(ppy)₃ to fabricate green PhOLEDs. The EQE_max values of devices G1 and G2 reach 12.9% and 12.7%, respectively, which are comparable to that of the reference host material 4,4′-di(9H-carbazol-9-yl)-1,1′-biphenyl (CBP) reported in our previous work.