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    Fluorene-based cathode interlayer polymers for high performance solution processed organic optoelectronic devices

    Year: 2014

    Journal: ORGANIC ELECTRONICS, Vol. 15, p 1244-1253, 20150722

    Authors: Xu, Weidong; Zhang, Xinwen; Hu, Qi; Zhao, Li; Teng, Xiaoyun; Lai, Wen-Yong; Xia, Ruidong; Nelson, Jenny; Huang, Wei; Bradley, Donal D. C.

    Organizations: Nanjing Univ Posts & Telecommun, Inst Adv Mat, Key Lab Organ Elect & Informat Displays, Nanjing 210023, Jiangsu, Peoples R China; Univ London Imperial Coll Sci Technol & Med, Dept Phys, London SW7 2AZ, England; Univ London Imperial Coll Sci Technol & Med, Ctr Plast Elect, London SW7 2AZ, England; Nanjing Tech Univ, Jiangsu Singapore Joint Res Ctr Organ Bioelect &, Inst Adv Mat, Nanjing 211816, Jiangsu, Peoples R China

    A hydrophilic polyfluorene-based conjugated polyelectrolyte (CPE) Poly[9,9-bis(4 '-(6 ''-(diethanolamino) hexyloxy) phenyl) fluorene], PPFN-OH (Scheme 1) has been synthesized and utilized as cathode interlayer for both polymer light emitting diodes (PLEDs) and solar cells (PSCs). For comparison, another CPE namely Poly[9,9-bis(6 '-(diethanolamino) hexyl) fluorene] (PFN-OH) has also been investigated. They comprise the same polyfluorene backbone structures with, respectively, diethanolaminohexyl (PFN-OH) and diethanolaminohexoxyphenyl (PPFN-OH) substituents attached to the C9 carbon of the fluorene repeat unit. In comparison to reference devices with more reactive Ca/Al cathodes, utilizing these CPEs as interlayers allowed an Al cathode to be used for blue light emission PLEDs, yielding 51% and 92% enhancement of maximum luminous efficiency (LE) for PFN-OH and PPFN-OH, respectively. The PLEDs with PPFN-OH showed both higher maximum LE and maximum luminance (L) (LE = 2.53 cd/A at 6.2 V, L = 9917 cd/m(2) at 8.3 V) than devices with PFN-OH (2.00 cd/A at 4.1 V, 3237 cd/m(2) at 7.2 V). The PPFN-OH PLEDs also showed no significant roll-off in efficiency with increasing current density up to 400 mA/cm(2), indicating excellent electron injection ability and stability for this interlayer. The insertion of alkoxy-phenyl groups at the C9-position in PPFN-OH is clearly advantageous. This simple modification significantly improves the CPE cathode interlayer performance. Parallel investigations of the electron extraction properties of PPFN-OH in inverted architecture PSCs with PCDTBT:PC70BM bulk heterojunction active layers demonstrated a power conversion efficiency enhancement of similar to 19% (from 4.99% to 5.95%) for indium tin oxide cathode devices compared with reference devices using Ca/Al cathodes. These results confirm PPFN-OH to be a promising interlayer material for high performance solution processed organic optoelectronic devices. (C) 2014 Elsevier B.V. All rights reserved.