Triazolobenzothiadiazole-Based Copolymers for Polymer Light-Emitting Diodes: Pure Near-Infrared Emission via Optimized Energy and Charge Transfer

Petri Murto, Alessandro Minotto, Andrea Zampette, Xiaofeng Xu, Mats R. Andersson, Franco Cacialli, Ergang Wang

    Research output: Contribution to journalArticlepeer-review

    25 Citations (Scopus)

    Abstract

    A series of new near-infrared (NIR) emitting copolymers, based on a low band gap 6-(2-butyloctyl)-4,8-di(thiophen-2-yl)-[1,2,3]triazolo[4′,5′:4,5]benzo[1,2-c]-[1,2,5]thiadiazole (TBTTT) fluorophore copolymerized into a high band gap poly[3,3′-ditetradecyl-2,2′-bithiophene-5,5′-diyl-alt-5-(2-ethylhexyl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione-1,3-diyl] (P2TTPD) host backbone, for polymer light-emitting diode (PLED) applications is reported. PLEDs fabricated from the host polymer (P2TTPD-0) show external quantum efficiencies (EQEs) up to 0.49% at 690 nm, with turn-on voltage (Von) at only 2.4 V. By incorporating the TBTTT segments into the host polymer backbone, pure NIR emission peaking at ca. 900 nm is obtained with Von remaining below 5 V. This work demonstrates that such a low Von can be attributed to efficient intrachain energy and/or charge transfer to the TBTTT sites. When the NIR emitting copolymer (P2TTPD-10) is blended with P2TTPD-0, the TBTTT are confined to well-separated polymer chains. As a result, the EQE from the blend is lower and the Von higher than that obtained from the pure copolymer (P2TTPD-1.0) with equal content of TBTTT. An analogous copolymer (P4T-1.0), consisting of poly[3,3′-ditetradecyl-2,2′:5′,2′′:5′′,2′′′-quaterthiophene-5,5′′′-diyl] (P4T) as the host and 1% TBTTT as the NIR emitter, further demonstrates that pure NIR emission can be obtained only through optimized molecular orbital energy levels, as in P2TTPD-1.0, which minimizes chances for either charge trapping or exciton splitting.

    Original languageEnglish
    Pages (from-to)2068-2076
    Number of pages9
    JournalAdvanced Optical Materials
    Volume4
    Issue number12
    DOIs
    Publication statusPublished - 2016

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