Homoleptic thiazole-based Ir^III phosphorescent complexes for achieving both high EL efficiencies and an optimized trade-off among the key parameters of solution-processed WOLEDs

Two homoleptic thiazole-based Ir^III phosphorescent emitters, Ir-3Tz1F and Ir-3Tz2F, with fluorinated 2-phenylthiazole-type ligands were designed and prepared. Their thermal stability, and photophysical and electrochemical properties, as well as electroluminescent (EL) performances in both monochromic OLEDs and solution-processed WOLEDs were investigated. When doped in monochromic OLEDs made by vacuum deposition, Ir-3Tz1F gave the maximum EL efficiencies with η_L of 56.2 cd A^-1, η_ext of 15.8% and η_p of 50.2 lm W^-1. Critically, solution-processed WOLEDs based on Ir-3Tz1F with three primary colors could achieve an excellent trade-off among the stable balanced white EL spectra, a high EL efficiency and a high color rendering index (CRI). The optimized solution-processed WOLED exhibited very attractive EL efficiencies of 33.4 cd A^-1, 16.5% and 30.6 lm W^-1, while maintaining both a high CRI of ca. 80 and very stable Commission Internationale de L'Eclairage (CIE) coordinates in a wide driving voltage range from 4 V to 11 V.