Highly Efficient Spiro[fluorene-9,9′-thioxanthene] Core Derived Blue Emitters and Fluorescent/Phosphorescent Hybrid White Organic Light-Emitting Diodes

Abstract

A series of blue emitters incorporating spiro[fluorene-9,9′-thioxanthene] or spiro[fluorene-9,9′-thioxanthene-S,S-dioxide] as the core and phenylcarbazole or triphenylamine as the arms were designed and synthesized. Their spiro conformation is beneficial for their thermal stability and for reducing the trend of aggregation quenching. By tuning the valence of the sulfur atom, highly efficient local excited (LE) state deep blue emitters and charge-transfer (CT) state blue emitters are obtained. The devices based on the LE emitters TPA-S and CzB-S as the nondoped emissive layer exhibit high external quantum efficiency of 1.76% and 2.03% and Commission Internationale de l’Eclairage (CIE) coordinates of (0.158, 0.039) and (0.160, 0.054), respectively, and their CIEy values are among the smallest ever reported for the deep blue OLEDs and are readily very close to that of the inorganic light-emitting diode [CIE (0.16, 0.02)]. The nondoped device based on the CT emitter TPA-SO2 as the emissive layer also exhibits a high current efficiency of 5.46 cd A–1 and CIE coordinates of (0.154, 0.168). To fully utilize the 25% singlet and 75% triplet excitons, fluorescent/phosphorescent hybrid white organic light-emitting diodes in a single-emissive-layer architecture were also fabricated with TPA-SO2 as the blue emitter as well as the host of orange phosphorescent emitter to give forward-viewing power efficiency of 47.9 lm W–1, which is the highest value ever reported for the devices in a similar architecture without using any out-coupling technology.