Twisted penta-Carbazole/Benzophenone Hybrid Compound as Multifunctional Organic Host, Dopant or Non-doped Emitter for Highly Efficient Solution-Processed Delayed Fluorescence OLEDs

A new multi-functional penta-carbazole/benzophenone hybrid compound 5CzBP was designed and synthesized through a simple one-step catalyst-free C—N coupling reaction by using 2,3,4,5,6-pentafluorobenzophenone and carbazole as starting materials. 5CzBP is very soluble in tetrahydrofuran (THF), which brings an environmentally friendly device fabrication for solution-processed OLEDs instead of most widely used chlorinated solvents when 5CzBP is employed as the bulk-phase of organic host or non-doped emitter in the emissive layer. 5CzBP exhibits thermally activated delayed fluorescence (TADF) characteristic with relatively high triplet energy of 2.60 eV and a low ΔE_ST of 0.01 eV. By using the new TADF material as organic host for another green TADF emitter, maximum external quantum efficiency (EQE) of 12.5% has been achieved in simple solution-processed OLED device. Besides, a maximum EQE of 8.9% and 5.7% was further obtained in TADF devices based on 5CzBP as dopant and non-doped emitter, respectively. The simultaneously acting as efficient TADF host and non-doped TADF emitter provides the potential guidance of the future simple single-layer two-color white OLEDs based on low-cost pure organic TADF materials.