Harvesting triplet states efficiently to produce energy efficient OLEDs Paloma L dos Santos University of Sheffield, UK Organic light emitting diodes (OLEDs) have become a central part of materials research, with the ever-growing requirement for more energy efficient, high colour purity, higher quality display devices. There is significant interest in OLED materials which converts dark triplet excited states to emissive singlet states. Two mechanisms can harvest triplet states using metal-free organic molecules: (i) thermally activated delayed fluorescence (TADF) and (ii) triplet–triplet annihilation (TTA). In this poster I will present two studies, which showcases the latest advances on molecular control to enhance triplet harvesting in different classes of materials and their application in devices. The first study highlights how to achieve efficient reverse intersystem crossing and high colour purity in TADF materials. Via careful design of a new Multiresonant MR-TADF material (Mes3DiKTa) [1], aggregation formation was supressed (one of the main challenges on the MR-TADF field), even at high doping concentrations. This allowed us to produce devices that show high energy efficiency (External Quantum Efficiency above 20%) and narrowband emission (FWHM below 40 nm). The second study presents the first observation of TTA from columnar liquid crystalline state [2]. We show how careful mix of materials with complementary functions (ColLC-A and ColLC-B) can activate the TTA mechanism. Combination of the two molecules in blends yields TTA from ColLC-A dimers fuelled by the triplet population on ColLC-B dimers. Important, the observation of delayed fluorescence in the condensed viscous fluid state of liquid crystal materials, where molecules can be uniformly oriented by annealing, opens the possibility to use such materials as emissive layers of OLEDs to enhance light outcoupling as well as charge and exciton transport, achieving energy efficient devices. References 1. David Hall, Subeesh Madayanad Suresh, Paloma L. dos Santos, Eimantas Duda, Sergey Bagnich, Anton Pershin, Pachaiyappan Rajamalli, David B. Cordes, Alexandra M. Z. Slawin, David Beljonne, Anna Köhler, Ifor D. W. Samuel, Yoann Olivier, and Eli Zysman-Colman, Adv. Optical Mater. 2020, 8, 1901627 2. Larissa G. Franca, Paloma L. dos Santos, Piotr Pander, Marília G. B. Cabral, RodrigoCristiano, Thiago Cazati, Andrew P. Monkman, Harald Bock and Juliana Eccher, ACS Appl. Electron. Mater. 2022, 4, 7, 3486–3494
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