Highly Efficient Red Phosphorescent OLEDs Based on Non-Conjugated Silicon-Cored Spirobifluorene Derivative Doped with Ir-Complexes

Abstract

A novel host material containing silicon-cored spirobifluorene derivative (SBP-TS-PSB), is designed, synthesized, and characterized for red phosphorescent organic light-emitting diodes (OLEDs). The SBP-TS-PSB has excellent thermal and morphological stabilities and exhibits high electroluminescence (EL) efficiency as a host for the red phosphorescent OLEDs. The electrophosphorescence properties of the devices using SBP-TS-PSB as the host and red phosphorescent iridium (III) complexes as the emitter are investigated and these devices exhibit higher EL performances compared with the reference devices with 4,4-N,N-dicarbazole-biphenyl (CBP) as a host material; for example, a (piq)2Ir(acac)-doped SBP-TS-PSB device shows maximum external quantum efficiency of ext = 14.6%, power efficiency of 10.3 lm W-1 and Commission International de L'Eclairage color coordinates (0.68, 0.32) at J = 1.5 mA cm-2, while the device with the CBP host shows maximum ext = 12.1%. These high performances can be mainly explained by efficient triplet energy transfer from the host to the guests and improved charge balance attributable to the bipolar characteristics of the spirobifluorene group.