New xanthone derivatives as host materials: Improvement of carriers balance for high-efficiency green phosphorescent OLEDs using two host materials

Three new xanthone derivatives, 3-(4-(diphenylamino)-9H-carbazol-9-yl)-9H-xanthen-9-one (XanCarDipha), 2-(4-(4-(diphenylamino)-9H-carbazol-9-yl)phenyl)-9H-xanthen-9-one (p-XanCarDipha), and 2-(3-(4-(diphenylamino)-9H-carbazol-9-yl)phenyl)-9H-xanthen-9-one (m-XanCarDipha) as host materials are designed and synthesized, and they are applied to the development of green phosphorescent organic light-emitting diodes (PHOLEDs). Due to the different connection methods of carbazole units and xanthone units of the compounds, the efficiency curves of XanCarDipha exhibited significantly difference compared to other two materials after above three new materials are made into OLED devices as single host in emitting layer (EML). In EML, a PHOLED using 1: 1 p-XanCarDipha: CarTria as double host and doped with 12 wt% tris(2-phenylpyridine) iridium as a guest material can achieve the uppermost external quantum efficiency (EQE) of 20.93%, the uppermost current efficiency (CE) of 77.40 cd A⁻¹, and the uppermost power efficiency (PE) of 93.15 lm W⁻¹. Compared with corresponding highest luminous efficiency of devices using p-XanCarDipha as single host material (16.86%, 62.55 cd A⁻¹ and 42.60 lm W⁻¹), the efficiency of double-host materials has been significantly enhanced. Meanwhile, the glass transition temperatures (T_g) of the three new host materials are all higher than 120 °C, indicating that they should have good thermal stability in the device application. This work not only provides a design direction for xanthones, but also demonstrates its superior performance on OLED devices when they combined with another host material.