Increased efficient copolymers with PFV and PPDFV for light emitting diodes

Abstract

New electroluminescent copolymers with fluoro groups in vinylene unit, poly(9,9-di-hexylfluorene-2, 7-vinylene-co-pphenylenedifluorovinylene) (PFVPDFV), have been synthesized by the GILCH polymerization. The fluoro groups were introduced on vinylene units to increase the electron affinities of the copolymers. The PFVPDFVs exhibit absorption spectra with maximum peaks at 371 ~ 413 nm. In the PL spectra of PFVPDFVs, as the PDFV content increases up to 50% in the copolymer system, fwhm was decreased by 4 - 38 nm as compared to PFV. The HOMO energy levels of the copolymers were about 5.25 - 5.50 eV, and the LUMO energy levels were about 2.67-2.97 eV. The polymer LEDs (ITO/PEDOT/polymer/Al) of PFVPDFVs showed emission with maximum peaks at around 472 - 538 nm. By adjusting the feed ratios of PDFV in the copolymers, it was possible to tune the emission colors from greenish yellow to orange depending on the obtained CIE coordinates. The luminescence efficiencies of the copolymers at room temperature are about 0.1-1.47 cd/A. The introduction of up to 50 % of PDFV in PFVPDFVS can enhance the device performance to result in high current density, brightness and efficiency due to the increased electron injection ability caused by the presence of fluoro groups in the vinylene units.