Novel V-Shaped Bipolar Host Materials for Solution-Processed Thermally Activated Delayed Fluorescence OLEDs

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) offer high efficiency for next-generation displays and lighting.
• Developing efficient host materials is crucial for optimizing TADF-OLED performance, especially for solution processing.
• V-shaped molecular architectures can influence charge transport and photophysical properties in organic electronic devices.

Purpose of the Study:

• To synthesize and evaluate novel V-shaped host molecules for solution-processed TADF-OLEDs.
• To investigate the structure-property relationships of unipolar (BBCzC, BTDC) and bipolar (BCzTC) host molecules.
• To determine the optimal host material for achieving high performance in green TADF-OLEDs.

Main Methods:

• Synthesis of three V-shaped host molecules: BBCzC, BTDC, and BCzTC, featuring 9-phenyl-9H-3,9'-bicarbazole (PBCz) and/or 2,12-di-tert-butyl-7-phenyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (PDBNA) moieties linked by a cyclohexane unit.
• Fabrication of solution-processed green TADF-OLEDs utilizing the synthesized host molecules and a green TADF emitter.
• Characterization of device performance, including external quantum efficiency (EQE), power efficiency, current efficiency, photoluminescence quantum yield (PLQY), and charge transport properties.

Main Results:

• All synthesized host molecules exhibited good solubility, enabling solution processing.
• The bipolar host molecule BCzTC demonstrated superior performance in TADF-OLEDs compared to unipolar hosts BBCzC and BTDC.
• The BCzTC-based device achieved a maximum external quantum efficiency of 30%, power efficiency of 71 lm W⁻¹, and current efficiency of 102 cd A⁻¹.

Conclusions:

• The bipolar BCzTC host molecule provides an excellent balance of hole and electron transport properties, leading to highly efficient energy transfer to the emitter.
• BCzTC's high photoluminescence quantum yield and favorable charge transport characteristics make it a promising host for high-performance, solution-processed TADF-OLEDs.
• The study highlights the potential of V-shaped bipolar host molecules in advancing TADF-OLED technology.