VIBRONIC STATES AND ELECTRONIC PROPERTIES OF ALUMINIUM JUNCTIONS WITH MELT-PROCESSED POLY[3-(2,5-DIOCTYLPHENYL)THIOPHENE] (PDOPT)

Abstract

Poly[3-(2,5-dioctylphenyl)thiophene] (PDOPT) becomes a semiconducting film when spin coated or caste from a chloroform solution. The optical absorption spectrum of spin coated thin films was measured using UVNis/NIR spectrophotometer which showed a forbidden energy gap of about 2.02 eV. In addition, two shoulders were observed on each side of the absorption peak. These kinks are the vibrational modes of double and single bonds in PDOPT that resonate
at shorter and longer wavelengths, respectively. The electronic properties of meltprocesGed PDOPT in the form of Al/PDOPT/ITO sandwich structure were analyzed using current-voltage characteristics and complex impedance spectroscopy. The I -V curves were found to be symmetrical and non-linear, where the current across the junction was limited by the series resistance due to the oxide of aluminium at the
AlIpDOPT interface governed by space charge limited current (SCLC). The impedance spectra (IS) showed part of a single semicircle on Cole-Cole co-ordinates manifesting one geometric capacitance. This is modelled by one parallel RC electrical circuit, usually obtained from metal-semiconductor (MS) devices.