Host–Dopant System To Generate Bright Electroluminescence from Small Organic Molecule Functionalized Light-Emitting Electrochemical Cells
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- 作者：Madayanad Suresh Subeesh ; Kanagaraj Shanmugasundaram ; Chozhidakath Damodharan Sunesh ; Ramesh Kumar Chitumalla ; Joonkyung Jang ; Youngson Choe
- 刊名：Journal of Physical Chemistry C
- 出版年：2016
- 出版时间：June 9, 2016
- 年：2016
- 卷：120
- 期：22
- 页码：12207-12217
- 全文大小：476K
- 年卷期：0
- ISSN：1932-7455
文摘
Albeit their easy accessibility and low cost, small organic molecules are not known for their high electroluminescence in light-emitting electrochemical cells (LECs). To construct a bright low-cost LEC device, the functions of charge transport and charge recombination should be separated in the active layer of LEC devices. Herein, we demonstrate that the widely used host–dopant strategy in organic light-emitting diodes (OLEDs) can significantly improve the electroluminescence from small organic molecule fueled LEC devices, provided the host molecules are carefully selected. Furthermore, performance of host–dopant small-molecule LEC devices hugely relies on the properties of host materials rather than the emitting luminophores. Conversely to the high performance of intramolecular charge-transfer (ICT) molecular systems in OLEDs, doped ICT fluorophores having a low-lying charge-transfer state can behave like exciton loss channels in the high ionic environment of LEC-active layers. Similar to the behavior of previously reported ICT molecules in polar solvents, our synthesized D−π-A−π-D phenanthroimidazole derivative exhibited fluorescence quenching and a huge blue shift of emission in the doped thin film of the ionic host. However, even with a less efficient emitter, high electroluminescence was achieved from a host–dopant LEC system. Our best device exhibited a maximum brightness of 5016 cd/m2 at a current efficiency of 0.73 cd/A. This device outplays our previously reported nondoped LEC (ihpypn-LEC) with a 7-fold increase in the maximum brightness and over a 3-fold increase in the current efficiency at peak brightness. To the best of our knowledge, these peak brightness values recorded here (device 2) are the best among those reported by small organic molecule LEC devices so far. This report reveals the potential of small organic molecules, especially phenanthroimidazole derivatives, in casting bright and efficient low-cost host–dopant LECs with minimum effort and appreciable sustainability.