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

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

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

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/m2 at 8.3 V) than devices with PFN-OH (2.00 cd/A at 4.1 V, 3237 cd/m2 at 7.2 V). The PPFN-OH PLEDs also showed no significant roll-off in efficiency with increasing current density up to 400 mA/cm2, 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 ∼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. © 2014 Elsevier B.V. All rights reserved.
Original languageEnglish (US)
JournalOrganic Electronics
Volume15
Issue number6
DOIs
StatePublished - Jan 1 2014
Externally publishedYes

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