Studies of MEH-PPV and MEH-PPV/MCMB Films and Their Light Absorption in the Red Wavelength Region of the Visible Spectrum Nor Diyana Abdul Aziz 1,2,a , Roshidah Rusdi 1,2,b , Norlida Kamarulzaman 2,c 1 Faculty of Applied Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selangor Malaysia 2 Centre for Nanomaterials Research, Institute of Science, Level 3 Block C Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia a diyana198@yahoo.com, b nur_taqwaiman@yahoo.com, c norlyk@salam.uitm.edu.my Keywords: MEH-PPV film, UV-Vis NIR, optical band gap. Abstract. Poly [2-methoxy, 5-(2-ethyl-hexyloxy)-p-phenylene-vinylene] (MEH-PPV) is a conjugated polymer that exhibit excellent luminescence properties in the visible spectrum. The fundamental absorption edge in the film is formed by the direct allowed transitions. In this work, free-standing films of MEH-PPV and MEH-PPV/MCMB were obtained by a solvent casting method. Mesocarbon Microbead (MCMB), a type of carbon, is added to the polymer producing composite films. The films were characterized by using the UV-Vis-NIR spectrophotometer. The film samples exhibited an absorption band in the red visible region. This is due to the electron transition between the non-localized bands. However, when MCMB is doped into the polymer matrix, the band absorption edge is red-shifted compared to that of the MEH-PPV pure film. Therefore, the optical band gaps of the composite films have decreased due to the presence of MCMB. Introduction Semiconductor devices based on organic semiconductors have been a growing interest of many researchers for many years. Conjugated polymers, especially MEH-PPV, are known as one of the most promising material for devices such as light emitting diode (LED), photovoltaic cells [2] and recently as a technology for full-colour displays [9]. This is due to the unique advantages of the conjugated polymers. Through the modification of morphology, polymeric structure via the film fabrication technique, optical, electronic, and electrochemical properties can be tuned for a specific application [5, 10]. About a decade or so since the first work of modification made on the electrical properties of conjugated materials, the band gap has become one of the important tuneable electronic properties. This is because, the magnitude of the band gap is a key to understanding conducting polymers. This can be seen in the LEDs and photovoltaic applications, where the value of the band gap is crucial as it plays a role in the colour of the emitted light in LEDs and the effectiveness with which solar radiation is absorbed in photovoltaic devices [6]. In this work, we are studying the effect of carbon on the optical band gap of the MEH-PPV pure and composite films by using UV-Vis-NIR spectroscopy. Experimental The MEH-PPV material obtained was synthesized using a modified Gilch method that has been discussed earlier in another paper [11]. Free standing films of pure MEH-PPV and MEH- PPV/MCMB composite were prepared by the solution casting technique. The MEH-PPV was dissolved in tetrahydrofuran (THF) and stirred overnight before casted onto Teflon Petri dish and allowed to dry at 50°C under vacuum oven for one hour. For the MEH-PPV/MCMB composite, a Advanced Materials Research Vol. 545 (2012) pp 308-311 Online available since 2012/Jul/09 at www.scientific.net © (2012) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.545.308 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 202.58.85.15-25/07/12,16:26:09)