This thesis details the fabrication and characterisation techniques used to improve our knowledge and understanding of the electrical and optical properties of conducting polymer devices. This particular study is based upon the continued characterisation of Schottky barrier diode structures prepared from electropolymerised film of poly(3-methylthiophene) (P3MeT) and concentrates on four main areas, (i) the nature and origin of acceptor states in partially dedoped poly(3-methylthiophene), (ii) the nature of the aluminium / polymer interface, (iii) the electrical and optical properties of P3MeT and (iv) improved understanding of the doping/ dedoping processes. Films were electropolymerised onto vanous substrates depending on the type of measurement and technique used. Gold-coated glass substrates were used as a basis for the formation of most Schottky barrier diodes used in electrical characterisation measurements, whjlst ITO coated glass was used for all optical characterisation and gold-coated silicon for all Raman measurements. However, in all cases, constant improvements to the adopted growing procedure resulted in repeatable, high quality, uniform films. DC, current-voltage (1-V) plots, and ac, frequency dependent, capacitance and loss measurements were used to characterise the electrical and optical properties of conducting polymer based diodes. Anomalies observed in these characteristics were studied and investigated, in particular with respect to the metal / polymer interface and the doping / dedoping processes. During this study, a number of new analytical techniques have been applied for the first time to conducting polymers. These include, Deep Level Transient Spectroscopy (DLTS), a technique commonly used to analyse acceptor states in inorganic semiconducting devices, in-situ Raman characterisation of the effects of film doping and dedoping and Atomic Force Microscopy (AFM) techruques which has been successfully used to characterise sample structure, roughness and thickness for assessing the quality and urufonnity of film samples.