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Issue 8, 2014
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Utilization of “thiol–ene” photo cross-linkable hole-transporting polymers for solution-processed multilayer organic light-emitting diodes

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Abstract

Solution-processable hole-transporting layers (HTLs) capable of cross-linking are especially important in solution-processed organic light-emitting diodes (OLEDs) to achieve multilayer structures with separated charge-transporting layers and emitting layers. In this work, we report the first example of photo cross-linked HTL adopting “thiol–ene” reaction. A new allyl-containing hole-transporting polymer, Allyl-TFB, has been synthesized and characterized by NMR, TGA, DSC, UV-vis spectroscopy, cyclic voltammetry, etc. The allyl ether moiety successfully participated in thiol–ene photo cross-linking to give cross-linked HTL. The solvent resistance of the cross-linked Allyl-TFB film was evaluated by changing the UV irradiation time from 5 to 240 seconds. In addition to cross-linking, fine patterning of Allyl-TFB with a photo-mask was also demonstrated. To ascertain the usefulness of our new photo cross-linkable HTL system in phosphorescent OLEDs, OLED devices with the configuration of [ITO/PEDOT:PSS/(Allyl-TFB)/26DCzPPy:Ir(mppy)3/TPBi/CsF/Al] were fabricated. There were large differences in device characteristics depending upon the UV irradiation time of HTL, that is to say, the less UV irradiated (30 s) device, Device-1, showed lower operating voltage and higher efficiency than the more UV irradiated (180 s) one, Device-2. This difference in device characteristics originated from the difference in hole-transporting property with UV irradiation time, which was confirmed by hole-only device characterization. Device-1 also showed a better performance than the control device containing no HTL or simple TFB. The maximum luminous efficiency and power efficiency of Device-1 adopting our new cross-linked Allyl-TFB HTL were 31.4 cd A−1 and 21.8 lm W−1, respectively. Based on these results, we expect that this type of thiol–ene photo cross-linking will find various applications in cross-linking and patterning of active organic electronic materials as well as OLED materials.

Graphical abstract: Utilization of “thiol–ene” photo cross-linkable hole-transporting polymers for solution-processed multilayer organic light-emitting diodes

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Publication details

The article was received on 24 Oct 2013, accepted on 28 Nov 2013 and first published on 02 Jan 2014


Article type: Paper
DOI: 10.1039/C3TC32098G
Citation: J. Mater. Chem. C, 2014,2, 1474-1481
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    Utilization of “thiol–ene” photo cross-linkable hole-transporting polymers for solution-processed multilayer organic light-emitting diodes

    J. Lee, H. Han, J. Lee, S. C. Yoon and C. Lee, J. Mater. Chem. C, 2014, 2, 1474
    DOI: 10.1039/C3TC32098G

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