A Wide-Bandgap, High-Mobility Electron-Transporting Material Containing a 9,9′-Spirobithioxanthene Skeleton

Abstract The efficiency and stability of organic light-emitting diodes (OLEDs) are highly dependent on the balance of carriers in the emitting layer. The lack of wide-bandgap and high-mobility electron-transporting material (ETM) has restricted the performance and processing of blue fluorescent OLEDs (FOLEDs) and green phosphorescent OLEDs (PHOLEDs) in the display industry. Herein, on the basis of a p-π conjugated 9,9′-spirobithioxanthene skeleton, a novel ETM with S and C atoms bridging phenylpyridine functional units (T3PySS) was designed and synthesized. Such a rigid and symmetrically orthogonal molecule exhibited a high triplet energy level of 2.7 eV and electron mobility comparable to the most conductive ETMs. The investigation on the bridge atom and the number of functional groups in this type of ETMs revealed that balanced inter- and intramolecular electron coupling was critical to achieving high-mobility, wide-bandgap ETM. The deep-blue FOLEDs (CIEy = 0.07) with a T3PySS electron-transporting layer reached a current density of 20 mA/cm2 and a luminescence of approximately 1000 cd/m2 at a voltage as low as 3.2 V while showing improved efficiency and stability compared to the control devices based on classical ETMs. Owing to improved charge balance, the stability of green PHOLEDs employing T3PySS was also superior to that of devices based on traditional high triplet energy ETMs.