A study on the electrical & optical characteristics of MEH-PPV thin films using different solution concentration

Polymer and organic light-emitting diodes (OLEDs), photovoltaic cells and field effect transistor are being focused towards commercialization. Poly [2-methoxy-5-(20-ethylhexoxy)-p-phenylene vinylene] or known as MEH-PPV, have been extensively studied for OLED applications. Thin film morphology much dependent on the solution concentration and choice of solvent which come out with different electrical and optical properties. MEH-PPV from two different solvents which are toluene and 1, 2-dichlorobenzene (1, 2-DCB) with varied concentration were prepared in this study. In order to have uniform thin film of MEH-PPV, spin coating technique is applied. The electrical properties of thin film were investigated and the optical properties were characterized by using UV-Visible-NIR (UV-VIS-NIR), Photoluminescence (PL) spectroscopy and Atom Force Microscope (AFM), high-resolution type of scanning probe microscopy. It is found that as the concentration of solution increased, thickness of thin film also increased as well as the resistivity of the thin film. However, MEH-PPV from 1, 2-DCB gives better conductivity compare to Toluene. There also significant difference between Toluene and 1, 2-DCB in PL and absorbance spectra which Toluene exhibit higher peak and more red-shifted compare to 1, 2-DCB.