Highly Efficient Simple-Structure Blue and All-Phosphor Warm-White Phosphorescent Organic Light-Emitting Diodes Enabled by Wide-Bandgap Tetraarylsilane-Based Functional Materials

Two host materials of {4-[diphenyl(4-pyridin-3-ylphenyl)silyl]phenyl}diphenylamine (p-PySiTPA) and {4-[[4-(diphenylphosphoryl)phenyl](diphenyl)silyl]phenyl}diphenylamine (p-POSiTPA), and an electron-transporting material of [(diphenylsilanediyl)bis(4,1-phenylene)]bis(diphenylphosphine) dioxide (SiDPO) are developed by incorporating appropriate charge transporting units into the tetraarylsilane skeleton. The host materials feature both high triplet energies (ca. 2.93 eV) and ambipolar charge transporting nature; the electron-transporting material comprising diphenylphosphine oxide units and tetraphenylsilane skeleton exhibits a high triplet energy (3.21 eV) and a deep highest occupied molecular orbital (HOMO) level (-6.47 eV). Using these tetraarylsilane-based functional materials results in a high-efficiency blue phosphorescent device with a three-organic-layer structure of 1,1-bis[4-[N,N-di(p-tolyl)-amino]phenyl]cyclohexane (TAPC)/p-POSiTPA: iridium(III) bis(4,6-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6)/SiDPO that exhibits a forward-viewing maximum external quantum efficiency (EQE) up to 22.2%. This is the first report of three-organic-layer FIr6-based blue PhOLEDs with the forward-viewing EQE over 20%, and the device performance is among the highest for FIr6-based blue PhOLEDs even compared with the four or more than four organic-layer devices. Furthermore, with the introduction of bis(2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1H-benzoimidazol-N,C-3)iridium acetylacetonate [(fbi)(2)Ir(acac)] as an orange emitter, an all-phosphor warm-white PhOLED achieves a peak power efficiency of 47.2 lm W-1, which is close to the highest values ever reported for two-color white PhOLEDs.