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Triazolobenzothiadiazole‐Based Copolymers for Polymer Light‐Emitting Diodes: Pure Near‐Infrared Emission via Optimized Energy and Charge Transfer
Author(s) -
Murto Petri,
Minotto Alessandro,
Zampetti Andrea,
Xu Xiaofeng,
Andersson Mats R.,
Cacialli Franco,
Wang Ergang
Publication year - 2016
Publication title -
advanced optical materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.89
H-Index - 91
ISSN - 2195-1071
DOI - 10.1002/adom.201600483
Subject(s) - materials science , copolymer , polymer , electroluminescence , oled , diode , band gap , optoelectronics , photochemistry , nanotechnology , chemistry , layer (electronics) , composite material
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)‐4 H ‐thieno[3,4‐ c ]pyrrole‐4,6(5 H )‐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 ( V on ) 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 V on remaining below 5 V. This work demonstrates that such a low V on 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 V on 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.