AUTHOR=Li Yungui , Wei Qiang , Cao Liang , Fries Felix , Cucchi Matteo , Wu Zhongbin , Scholz Reinhard , Lenk Simone , Voit Brigitte , Ge Ziyi , Reineke Sebastian 

TITLE=Organic Light-Emitting Diodes Based on Conjugation-Induced Thermally Activated Delayed Fluorescence Polymers: Interplay Between Intra- and Intermolecular Charge Transfer States

JOURNAL=Frontiers in Chemistry

VOLUME=7

YEAR=2019

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2019.00688

DOI=10.3389/fchem.2019.00688

ISSN=2296-2646

ABSTRACT=<p>In this work, interactions between different host materials and a blue TADF polymer named P1 are systematically investigated. In photoluminescence, the host can have substantial impact on the photoluminescence quantum yield (PLQY) and the intensity of delayed fluorescence (<italic>Φ</italic><sub>DF</sub>), where more than three orders of magnitude difference of <italic>Φ</italic><sub>DF</sub> in various hosts is observed, resulting from a polarity effect of the host material and energy transfer. Additionally, an intermolecular charge-transfer (CT) emission with pronounced TADF characteristics is observed between P1 and 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T), with a singlet-triplet splitting of 7 meV. It is noted that the contribution of harvested triplets in monochrome organic light-emitting diodes (OLEDs) correlates with <italic>Φ</italic><sub>DF</sub>. For devices based on intermolecular CT-emission, the harvested triplets contribute ~90% to the internal quantum efficiency. The results demonstrate the vital importance of host materials on improving the PLQY and sensitizing <italic>Φ</italic><sub>DF</sub> of TADF polymers for efficient devices. Solution-processed polychrome OLEDs with a color close to a white emission are presented, with the emission of intramolecular (P1) and intermolecular TADF (PO-T2T:P1).</p>