High brightness deep blue/violet fluorescent polymer light-emitting diodes (PLEDs)

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2015-01, Vol.3 (37), p.9664-9669
• Main Authors: Cook, Javan H., Santos, José, Al-Attar, Hameed A., Bryce, Martin R., Monkman, Andrew P.
• Format: Article
• Language: English
• Subjects: Aluminum; Brightness; Copolymers; Devices; Electric potential; Emission; Light-emitting diodes; Monomers
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/C5TC02162F

Two new deep blue/violet emitting alternating co-polymers, comprising readily-available carbazole (C) and fluorene (F) monomer units, have been synthesised and shown to produce extremely bright solution-processed polymer light-emitting diodes (PLEDs) with the structure ITO/PEDOT:PSS/polymer/TPBi/LiF/Al. The para -conjugated polymer, CF1 , gave PLED devices with external quantum efficiency (EQE) values of η ext,max 1.4%, L max of 565 cd m −2 with CIE x,y (0.16, 0.07). The EQE was raised to η ext,max 2.1%, after the addition of a TAPC hole injection layer. For the isomeric meta -conjugated polymer, CF2 , values of η ext,max 0.35%, L max of 16 cd m −2 with CIE x,y (0.18, 0.12) were obtained. The λ ELmax was 409 nm for both the CF1 and CF2 devices. The CF1 devices also possess low turn-on and low operating voltages for devices of such high brightness. Moreover, the CF1 emission is very stable from 10 cd m −2 up to peak brightness, with only a negligible shift in CIE coordinates. The combination of a simple co-polymer structure synthesised using readily-available monomer units, and high brightness and good colour stability from a simple device architecture, makes CF1 suitable for a wide range of applications requiring deep blue/violet emission.