Efficient aggregation-induced delayed fluorescent materials based on bipolar carrier transport materials for the fabrication of high-performance nondoped OLEDs with very small efficiency roll-off

Abstract

Thermally activated delayed fluorescent emitters generally require a complicated doping technique for their application in organic light-emitting diodes (OLEDs) and suffer from sharp efficiency roll-off at high luminance. To address this issue, herein, two new compounds, 35DCPP-BP-PXZ and 26DCPP-BP-PXZ, are synthesized by grafting functional groups with aggregation-induced delayed fluorescence (AIDF) to bipolar carrier transport materials. The electronic structures, electrochemical properties, thermal stabilities and photophysical properties of the generated compounds are investigated systematically, and the structure–property relationship is depicted. Both compounds enjoy high thermal and electrochemical stabilities, and show noticeable AIDF properties with strong delayed fluorescence and high photoluminescence efficiencies in neat films. In addition, they possess excellent bipolar carrier transport abilities, with almost identical hole and electron mobilities in neat films. Efficient nondoped OLEDs using both compounds as light-emitting layers are fabricated, affording high external quantum efficiencies of up to 17.3% and 16.1%. Notably, the device of 35DCPP-BP-PXZ has a tiny efficiency roll-off of 0.6% at 1000 cd m⁻² and the efficiency roll-off is only 16.2% even at an extremely high luminance of 10 000 cd m⁻², demonstrating the superb efficiency stability. These results potently prove the feasibility of the molecule design strategy of incorporating AIDF groups with bipolar carrier transport materials, which may bring about more robust luminescent materials for high-performance OLEDs.