Triphenylamino or 9-phenyl carbazolyl-substituted pyrimidine-5-carbonitriles as bipolar emitters and hosts with triplet harvesting abilities |
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Authors: | U Tsiko D Volyniuk V Andruleviciene K Leitonas G Sych O Bezvikonnyi V Jasinskas V Gulbinas P Stakhira JV Grazulevicius |
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Institution: | 1. Department of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu Pl. 19, LT-50254, Kaunas, Lithuania;2. Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, 38000 Grenoble, France;3. Center for Physical Sciences and Technology, LT-10257, Vilnius, Lithuania;4. Lviv Polytechnic National University, S. Bandera 12, 79013, Lviv, Ukraine |
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Abstract: | To obtain highly efficient organic semiconductors exhibiting fast emission decays, triplet-harvesting abilities and good bipolar charge-transporting properties for optoelectronic applications, compounds containing triphenylamine or 9-phenylcarbazole as donor moieties and pyrimidine-5-carbonitrile as electron-withdrawing unit were synthesised. Toluene solutions of the compounds demonstrated high photoluminescence quantum yields reaching 98%. As required for electroluminescent device applications, compound containing triphenylamino moiety showed high mobilities of both electrons and holes, which reached 4.4 × 10?4 cm2/V × s and 7.3 × 10?3 cm2/V × s, respectively at electric field of 3.6 × 105 V/cm. This triplet-harvesting mechanism was confirmed by the theoretical and experimental studies including a femtosecond transient absorption pump?probe technique and time-resolved electroluminescence spectroscopy. Pure-blue and greenish-blue fluorescent organic light-emitting diodes (OLEDs) with external quantum efficiency (EQE) reaching 7% and 6%, corresposndingly, were obtained using the newly synthesised compounds as emitters. The operation time (T50) of ca. 650 h were observed for blue OLED and of ca. 3800 h for greenish-blue OLED until reaching the half initial brightness (100 cd/m2). EQE of more than 20% and T50 exceeding 20,000 h were observed for electroluminescent devices based on emitter characterised by triplet?triplet annihilation and thermally activated delayed fluorescence which was utilised to test hosting properties of the differently donor-substituted pyrimidine-5-carbonitriles. |
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Keywords: | Hot-exciton Bipolar charge-transport Operation time Organic light-emitting diode pyrimidine-5-carbonitrile |
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