Structural Modification of Asymmetric Electron-Blocking Materials for Stable Blue Phosphorescent Organic Light-Emitting Diodes
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Blue phosphorescent organic light-emitting diodes (PhOLEDs) have been suffered from triplet leakage, resulted in rapid degradation of the device performance and efficiency roll-off. In this reason, electron-blocking materials (EBMs) with high triplet energy levels (ET) have been introduced, but their large energy bandgaps often increase turn-on voltages (Von) of PhOLEDs. Herein, we present a design strategy of asymmetric EBMs for effective triplet confinement and reduced Von of blue PhOLEDs. Four EBMs with high ET are developed based on ortho-linked donor–π–acceptor configurations by controlling photophysical properties and electrostatic interactions through fine-tuning of molecular twist and rigidity. The most twisted compound is revealed to have a preferential molecular orientations for hole transporting, concluded to significant improvements in power efficiency and operational stability of blue PhOLEDs.