Optoelectronic properties of semiconducting polymers and related applications

Since the discovery of semiconducting (conjugated) polymers in 1977 by Heeger, MacDiarmid and Shirakawa, a wide variety of electrical and optical devices have been developed using semiconducting polymers, such as light-emitting diodes, photodetectors, and fluorescent biosensors. All the devices are based on the electro-optical or optoelectronic properties of conjugated polymers. So understanding the fundamental electronic structures is of particular importance.; A general picture of electronic excitation of PPV upon photoexcitation remains a subject of intense debate. I addressed this problem by studying the photoconductivity excitation profile of aligned PPV sample with polarized light parallel and perpendicular to the chain axis. The spectral signature of the exciton is observed in the excitation profile as a narrow peak that emerges just below the band edge upon increasing the external field, the defect density or the temperature. The exciton binding energy is obtained from the energy of the narrow exciton peak with respect to the band edge, and independently, from analysis of the field dependence and temperature dependence of the exciton dissociation: E_b ∼ 60 meV.; The fluorescence quenching of luminescent polymers by electron acceptors through photoinduced charge transfer opens a new opportunity for conjugated polymers in biological and chemical sensors for use in medical diagnostics and toxicology. A comprehensive studies of the quenching mechanisms in two polymer:quencher systems in solutions are presented. The basic quenching mode is identified by carefully studying the buffer ions' effects, absorption profile, and temperature effects.; Finally, an application of photodetector utilizing conjugated polymers is presented. A large area photodetector is demonstrated to have true color (24 bit) resolution.