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

Abstract

Three V-shaped host molecules with a cyclohexane linker were successfully synthesized for thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs). The unipolar host molecules, BBCzC and BTDC, contained two 9-phenyl-9H-3,9′-bicarbazole (PBCz) moieties and two 2,12-di-tert-butyl-7-phenyl-5,9-dioxa-13b-boranaphtho­[3,2,1-de]­anthracene (PDBNA) moieties, respectively. BCzTC, a bipolar host molecule, consisted of a donor unit, PBCz, and an acceptor unit, PDBNA, connected by a cyclohexane linker. Three host molecules showed good solubility in various organic solvents, making them suitable for solution processing. Among the solution-processed green TADF-OLEDs using three host molecules and a green TADF emitter, the one with BCzTC showed the highest external quantum efficiency of up to 30% with a high power efficiency of 71 lm W–1 and a current efficiency of 102 cd A–1. Compared with BBCzC and BTDC, BCzTC exhibited a relatively high photoluminescence quantum yield (PLQY), an excellent balance in hole and electron transport properties in the emitting layer, and more efficient energy transfer to the emitter, giving such an excellent device performance.

V-shaped donor–acceptor organic emitters. A new approach towards efficient TADF OLED devices

“…Notably, V-shaped but non-conjugated compounds have been solely used as host TADF materials. 14 Adopting a new design strategy, we recently demonstrated that a nitrogen-doped polycyclic aromatic hydrocarbon (N-PAH) scaffold incorporating dibenzazepine (see Fig. 1) can provide the basis for efficient TADF emitters.…”

Rational Molecular Design Strategy for Host Materials in Thermally Activated Delayed Fluorescence-OLEDs Suitable for Solution Processing

“…These molecular structures are completely different from the structure of the Vshaped host molecule with cyclohexane-1,1-diyldibenzene as the linker that was previously developed. 24 In particular, the novel synthetic method that introduces two carbazoles directly into cyclohexane to enable a V-shaped host structure represents a significant innovation. By combining two smallmolecule hosts with this new non-conjugated sp 3 cyclohexane linker, it was possible to double the molecular weights of various carbazole-based small-molecule host materials while maintaining the singlet and triplet energies (S 1 and T 1 ).…”

Universal Polymeric Hole Transporting Material for Solution-Processable Green and Blue Thermally Activated Delayed Fluorescence OLEDs

“…Consequently, the orthogonal solvent system is selected based on the difference in the solubility of the materials used for the HTL and EML in organic solvents. − As a typical example, poly­( N -vinyl carbazole) (PVK), which has been used as an HTM in the past for the manufacture of OLED devices by solution processes, is readily soluble in chlorobenzene but not in toluene. Therefore, the upper light-emitting layer could be deposited on the PVK HTL using a toluene solution containing various hosts and emitters. , Although PVK has excellent characteristics such as a high glass transition temperature ( T g ) and high triplet energy ( T 1 ) value, the disadvantages of relatively poor hole mobility and fixed energy levels remain a challenge …”