The band gap tuned, LEP doped polymer films for plastic electronic devices

Abstract

Poly [2-methoxy-5(3,’7’-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV), is a light emitting polymer widely used in plastic electronic devices like LED, OFET & Solar cell. Reports indicate that MDMO-PPV film cast from chloroform has the absorption maximum at 491 nm with onset wavelength 577 nm which corresponds to a band gap of 2.15 eV between Highest Occupied Molecular Orbit (HOMO) and Lowest Un-occupied Molecular Orbit (LUMO). The present work is focused on lowering/tuning this band gap by doping MDMO-PPV on Poly Vinyl Acetate (PVAc) as the host insulating polymer matrix. Solutions of MDMO-PPV and PVAc are prepared in chloroform and films are obtained from solution cast method by doping MDMO-PPV at 0.5%, 1%, 2%, & 3.0 % by weight of PVAc. Films are characterized by Jasco UV-Vis NIR V 670 spectrometer which revealed the red shift in absorption maximum toward higher doping concentration. Red shift is maximum for 3% doped film with absorption peak at 554 nm and the onset wavelength at 654 nm. There is reduction in the band gap by of PVAc from 4.8 eV to 1.9eV and in turn the band gap of MDMO-PPVis reduced from 2.15 eV to 1.9eV.The electrical conductivity and dielectric properties, measured by Agilent 4294A Precision Impedance Analyzer resulted in increase in the conductivity and dielectric constant with doping level at higher frequencies. The thermal studies are done with the instrument Universal TA-SDT Q600. Structural studies are made using IR-Prestige-21 FTIR Spectrometer SHIMADZU that confirmed small interaction between the host matrix and the dopant. The light emission property is also investigated by exciting with 340nm in which the emission peak shows a blue shift of 9 nm towards the least doped sample with respect to pure MDMO-PPV. These band gap tuned polymer films are found to be promising materials for electro-optics, nano electronic devices. The new material can be used to devise LEDs, OPVs, OFETs etc. The device construction using these new films is the work under progress.