Solution‐Processable Pure Green Thermally Activated Delayed Fluorescence Emitter Based on the Multiple Resonance Effect

Abstract

Thermally activated delayed fluorescence (TADF) materials based on the multiple resonance (MR) effect are applied in organic light‐emitting diodes (OLEDs), combining high color purity and efficiency. However, they are not fabricated via solution‐processing, which is an economical approach toward the mass production of OLED displays. Here, a solution‐processable MR‐TADF material (OAB‐ABP‐1), with an extended π‐skeleton and bulky substituents, is designed. OAB‐ABP‐1 is synthesized from commercially available starting materials via a four‐step process involving one‐shot double borylation. OAB‐ABP‐1 presents attractive photophysical properties, a narrow emission band, a high photoluminescence quantum yield, a small energy gap between S1 and T1, and low activation energy for reverse intersystem crossing. These properties are attributed to the alternating localization of the highest occupied and lowest unoccupied molecular orbitals induced by the boron, nitrogen, and oxygen atoms. Furthermore, to facilitate charge recombination, two novel semiconducting polymers with similar ionization potentials to that of OAB‐ABP‐1 are synthesized for use as interlayer and emissive layer materials. A solution‐processed OLED device is fabricated using OAB‐ABP‐1 and the aforementioned polymers; it exhibits pure green electroluminescence with a small full‐width at half‐maximum and a high external quantum efficiency with minimum efficiency roll‐off.

A Brief History of OLEDs—Emitter Development and Industry Milestones

“…[ 84 ] Furthermore, Hatakeyama and co‐workers reported a solution‐processable OLED with the EQE of 21.8% and pure green emission of 505 nm, companied with an FWHM of 33 nm, through the use of the emitter OAB‐ABP‐1 which is depicted in Figure 9. [ 85 ] These excellent performances show the promising potential of a multi‐resonance design strategy to construct TADF emitter for application in OLEDs.…”

A Facile Synthesized Polymer Featuring B‐N Covalent Bond and Small Singlet‐Triplet Gap for High‐Performance Organic Solar Cells

“…reported a B‐N covalent bond containing tetrabenzopentacene, which exhibited a prominent hole mobility [12] . Moreover, boron atom exhibits opposite resonance effect to nitrogen atom, which can effectively separate the highest occupied molecular orbital (HOMO) level and the lowest unoccupied molecular orbital (LUMO) level [20, 21] . Therefore, small energy gap (Δ E ST ) between singlet (S 1 ) and triple state (T 1 ) can be realized in B‐N covalent bond containing conjugated materials (Figure 1 a).…”

“…[12] Moreover, boron atom exhibits opposite resonance effect to nitrogen atom, which can effectively separate the highest occupied molecular orbital (HOMO) level and the lowest unoccupied molecular orbital (LUMO) level. [20,21] Therefore, small energy gap (DE ST ) between singlet (S 1 ) and triple state (T 1 ) can be realized in B-N covalent bond containing conjugated materials (Figure 1 a). [20,21] This strategy has been proved successful in constructing thermally activated delayed fluorescence materials.…”

“…[20,21] Therefore, small energy gap (DE ST ) between singlet (S 1 ) and triple state (T 1 ) can be realized in B-N covalent bond containing conjugated materials (Figure 1 a). [20,21] This strategy has been proved successful in constructing thermally activated delayed fluorescence materials. [20,21] In OSCs, small DE ST is helpful to suppress the recombination from charge transfer (CT) state to triplet state.…”

“…[20,21] This strategy has been proved successful in constructing thermally activated delayed fluorescence materials. [20,21] In OSCs, small DE ST is helpful to suppress the recombination from charge transfer (CT) state to triplet state. [22][23][24] Besides, organic semiconductors containing boron-nitrogen coordinate bond (B !…”