Synthesis and characterization of a novel fluorene and selenophene -based copolymer in light-emitting diode and field effect transistor

Abstract

The materials containing selenium have recently been attracting much attention in light emitting diode(LED) and field effect transistor (FET).We have synthesized a new soluble conjugated copolymer (F8Se2) derived from 9,9-dioctylfluorene and 2,2-biselenophene by the palladium-catalyzed Suzuki coupling reaction. The synthesized polymer was characterized by $^1H$ NMR, UV-vis spectroscopy, PL, TGA and GPC. Also, we confirmed that F8Se2 is thermotropic liquid crystalline polymer with aligned structure from DSC, PLM and XRD analysis. EL device constructed with configuration of ITO/PEDOT:PSS/polymer/Ca/Al exhibited high brightness (1200 cd/㎡) at 10.5 V and low turn-on voltage (3.5 V). The significant red shift of the emission of Se-containing copolymer in comparison with its sulfur analogue, poly-9,9-dioctylfluorene-alt-bithiophene (F8T2), is attributed to the electron-donating property of selenium and strong interaction between biselenophene moiety in neighboring copolymer chains. Also, solution-processed FET of F8Se2 polymer was successfully fabricated using bottom-contact geometry and showed the typical p-channel field effect transistor characteristics. The measured field effect mobility of the transistor was $0.5×10^{-2}㎠/Vs$ and the on/off ratio was $1 ×10^4$.