From Event: SPIE Organic Photonics + Electronics, 2017
Multilayered small-molecule organic light-emitting diodes (OLEDs) have been commonly used for balanced charge transport and exciton confinement. However, standard method that uses high-vacuum deposition for multilayered OLEDs entails high material and fabrication cost, and it has been a critical impediment to low-cost production. Solution-processing of small-molecule OLEDs has been considered as a promising method, but limited luminous efficiency of solution-processed OLEDs have also been a hurdle for practical use. Therefore, high-efficiency in solution-processed small-molecule OLEDs with a simple device structure should be developed. Here, we report highly efficient solution-processed simplified OLEDs using novel electron-transporting host materials based on tetraphenylsilane with pyridine moieties. These host materials have high triplet energy levels (> 2.8 eV), wide band gaps (> 4.0 eV), and high glass transition temperature. We additionally used multifunctional polymeric hole injection layer and mixed-host emitting layer to achieve simple device architecture without hole transporting or electron blocking layer. Our novel electron transporting host materials which have higher electron transporting ability and triplet energy levels than that of conventional electron transporting host material (2,2′,2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)) provided more balanced charge transport and efficient energy transfer preventing backward energy transfer from phosphorescent dopants to host. Orange-red (~97.5 cd/A), green (~101.5 cd/A), and white (~74.2 cd/A) solution-processed phosphorescent OLEDs with simple device structure showed the highest recorded electroluminescent efficiencies of solution-processed OLEDs without additional light outcoupling structure reported to date. We also demonstrated a solution-processed flexible solid-state-lighting device as a potential application.
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