| Organic semiconductors, which are characterized by delocalized {dollar}{bsol}pi{dollar}-electron orbitals, are unique among the class of organic materials. Associated with these distortable {dollar}{bsol}pi{dollar} electron systems are strong linear and nonlinear optical interactions, making these materials potentially attractive for opto-electronic device applications.; Conjugated polymers, part of the general class of organic semiconductors, possess strong electron-lattice interactions, which are manifested in the form of nonlinear excitations known as solitons and polarons, and can lead to very large nonlinear optical susceptibilities with fast response times. Third harmonic generation (THG) experiments, which yield a value for the third order nonlinear optical susceptibility within the {dollar}{bsol}pi-{bsol}pi{bsol}sp*{dollar} energy gap, have been used to characterize these excitations for a degenerate ground state conjugated polymer. It is found that this system exhibits a large nonlinear optical response, with values for {dollar}{bsol}chi{bsol}sp{lcub}(3){rcub}{bsol} (3{bsol}omega){dollar} exceeding {dollar} 10{bsol}sp{lcub}-10{rcub}{dollar} esu, in accordance with theory.; Light-emitting diodes (LEDs) fabricated using organic semiconductors have generated a tremendous amount of interest. Although these devices have exhibited impressive characteristics, short device lifetimes continue to be a problem. In an effort to better understand these processes, electroluminescence (EL) degradation mechanisms were studied on small molecular organic LEDs using optical, photoluminescence (PL), and electroluminescence microscopies. Processes responsible for the EL degradation were identified, and were attributed to black spot formation, space charge accumulation, film re-crystallization, and chemical reactions.; An entirely new organic device architecture, the polymer grid triode (PGT), is also presented. This structure, which consists of a porous network of conducting polyaniline (PANI) surrounded by a semiconducting material, and sandwiched between two electrodes, is a three terminal device capable of current gain, similar to conventional inorganic transistors. An analytic model is presented to describe the behavior of this device, and it is found that predicted I-V and gain curves are in good agreement with experiment. Furthermore, a new class of PGT, fabricated using fullerenes, is discussed, and it is shown that these new devices exhibit superior transport characteristics relative to previously reported PGT systems. |
