Rational Molecular Design Enables Efficient Blue TADF−OLEDs with Flexible Graphene Substrate

• Published in: Advanced functional materials 2022-11, Vol.32 (47), p.n/a
• Main Authors: Sharif, Parisa, Alemdar, Eda, Ozturk, Soner, Caylan, Omer, Haciefendioglu, Tugba, Buke, Goknur, Aydemir, Murat, Danos, Andrew, Monkman, Andrew P., Yildirim, Erol, Gunbas, Gorkem, Cirpan, Ali, Oral, Ahmet
• Format: Article
• Language: English
• Subjects: 2D materials; blue OLEDs; flexible OLEDs; Graphene; graphene anodes; heavy atom effect; Indium tin oxides; Materials science; OLEDs; Organic light emitting diodes; Selenium; Substrates; TADF
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202207324

Observation of thermally activated delayed fluorescence (TADF) in conjugated systems redefined the molecular design approach to realize highly efficient organic light emitting diodes (OLEDs) in the early 2010s. Enabling effective reverse intersystem crossing (RISC) by minimizing the difference between singlet and triplet excited state energies (ΔEST) is proven to be a widely applicable and fruitful approach, which results in remarkable external quantum efficiencies (EQE). The efficacy of RISC in these systems is mainly dictated by the first‐order mixing coefficient (λ), which is proportional to spin‐orbit coupling (HSO) and inversely proportional to ΔEST. While minimizing ΔEST has been the focus of the OLED community over the last decade, the effect of HSO in these systems is largely overlooked. Here, molecular systems with increased HSO are designed and synthesized by substituting selected heteroatoms of high‐performance TADF materials with heavy‐atom selenium. A new series of multicolor TADF materials with remarkable EQEs are achieved. One of these materials, SeDF‐B, results in pure blue emission with EQEs approaching 20%. Additionally, flexible graphene‐based electrodes are developed for OLEDs and revealed to have similar performance as standard indium tin oxide (ITO) in most cases. These devices are the first report of TADF based OLEDs that utilize graphene‐based anodes. The work here describes a new design principle for TADF‐OLED materials, utilization of heavy atom selenium in donor segments, which results in enhanced reverse intersystem crossing and significant EQEs. The first ever utilization of graphene electrodes in flexible OLEDs with TADF‐based emitting layers and pure blue emitting devices with EQEs over 25% is also highlighted.