Novel Spiro Core‐Based Hole Transport Materials for Stable Deep‐Blue OLEDs with LT95 Over 420 h

• Published in: Advanced optical materials 2023-12, Vol.11 (23), p.n/a
• Main Authors: Jiang, Zhuonan, Yan, Hao, Zhang, Xiaopeng, Meng, Zhiming, Kuang, Changchun, Zhang, Xinkang, He, Yaowu, Zhu, Yanan, Meng, Hong
• Format: Article
• Language: English
• Subjects: Carrier density; Current carriers; deep‐blue OLED; device lifetime; Displays; Energy of dissociation; Excitons; Free energy; Functional materials; Heat of formation; high efficiency; hole transport materials; Molecular orbitals; Organic light emitting diodes; Quantum efficiency; spiro core
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.202301014

Flexible, lightweight, and cost‐effective organic light‐emitting diodes (OLEDs) show great promise for use in displays and lighting applications. However, creating highly efficient and stable deep‐blue OLEDs remains a challenge due to a lack of efficient functional materials, specifically hole transport materials (HTM). In this report, two new spiro‐HTMs are introduced with fluorene (FBP‐SFX) or dibenzofuran (DBF‐SFX) peripheral substituents. This study finds that the DBF‐SFX variant produces highly efficient deep‐blue OLEDs with a narrow emission (full‐width at half‐maximum FWHM of 25 nm) and the highest external quantum efficiency (EQE) of 33.2% among the FBP‐SFX (12.2%) and NPB (11.9%) variants. The superior performance of DBF‐SFX is attributed to its deeper highest occupied molecular orbital level (HOMO) and small trap density, which results in reduced band‐edge offset, lower turn‐on voltages, and balanced charge carrier densities. Importantly, the blue fluorescence OLED with DBF‐SFX displays exceptional device stability with LT95 over 420 h with an initial luminance of 1000 cd m−2. This is due to the stronger bond dissociation energy (BDE) and suppressed Exciton–Polaron Annihilation (EPA) using the dibenzofuran substituent. This work demonstrates a new HTM design approach using a spiro‐core architecture and dibenzofuran substituents to create efficient and long‐lasting deep‐blue OLEDs. Establishing a barrier‐free device and suppressing the Exciton–Polaron Annihilation effect are promising strategies for highly efficient and stable deep‐blue organic light‐emitting diodes (OLEDs). Two novel spiro‐core hole transport materials (HTMs) are synthesized with a deep highest occupied molecular orbital energy level and strong bond dissociation energy. As a result, the blue thermally activated delayed fluorescent device based on DBF‐SFX shows 33.2% EQEmax and the blue Triplet–Triplet Annihilation device based on DBF‐SFX shows outstanding device stability with LT95 over 420 h with an initial luminance of 1000 cd m−2. Overall, the HTMs design rule proposed in this work offers an effective method for producing highly efficient and stable blue OLEDs.