Advancing MR‐TADF OLED Toward True‐Blue CIE Value via Asymmetric Host Materials with Amorphous Morphology

• Published in: Advanced optical materials 2024-07, Vol.12 (19), p.n/a
• Main Authors: Han, Chih‐Pin, Shi, Emily Hsue‐Chi, Chen, Chieh An, Hsu, Chao‐Hsien, Chen, Chia‐Hsun, Wu, Chi‐Chi, Lee, Yi‐Ting, Chiu, Tien‐Lung, Lee, Jiun‐Haw, Leung, Man‐kit, Chou, Pi‐Tai
• Format: Article
• Language: English
• Subjects: Amorphous materials; Asymmetry; Emitters; host material; Morphology; multiple resonance‐induced thermally activated delayed fluorescence (MR‐TADF); organic light emitting diode (OLED); Organic light emitting diodes; Quantum efficiency; Vapor deposition
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.202303295

The new host materials are reported to boost the multiple resonance‐induced thermally activated delayed fluorescence (MR‐TADF) based pure deep‐blue organic light emitting diodes (OLEDs) toward further shortening the emission full width at the half maximum (FWHM). Based on an unusual asymmetric design concept, two new host compounds Bz2cb and Bz2cbz are synthesized. Despite possessing a compact and rigid molecular packing in crystal, Bz2cbz shows pure amorphous morphology via vapor deposition, as confirmed by the grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) analysis. Via incorporating a promising MR‐TADF emitter, ν‐DABNA‐O‐Me, into Bz2cb and Bz2cbz films, highly pure deep‐blue OLEDs are successfully demonstrated. Remarkably, the Bz2cbz device exhibits a 464 nm electroluminescence (EL) with narrow FWHM of 22 nm, accompanied by the reduction of the 0–1 vibronic sideband, and a maximum external quantum efficiency (EQEmax) of 28.2%, which, overall, reaches the true‐blue Commission Internationale de l'Eclairage coordinates (CIE) of (0.13, 0.07) and the high blue index of 253. The amorphous film formation turns out to be an important factor that is previously unrecognized to externally fine‐tune the MR‐TADF OLEDs toward even higher color purity. As a result, the device fabricated by MR‐TADF compound ν‐DABNA‐O‐Me hosted by Bz2cbz has attained a blue index that goes up to as high as 253, and better device performance in terms of EQEmax, CEmax, PEmax, and blue index compared to those using mCBP and mCP as the host materials.