| Operating characteristics of molecular organic devices are largely governed by the formation of excitons, and exciton interactions with interfaces between dissimilar materials. The study of these excitonic processes and their implementation in practical optoelectronic applications is the focus of this work. We demonstrate a number of novel molecular organic devices by utilizing unique optical and electronic properties of this class of solids.; Excitons dominate the fundamental processes in organic materials determining their absorption, photoconduction, luminescence, and lasing characteristics. The spatial extent of the exciton governs its dynamics and depends on the strength of intermolecular interaction. Different types of excitons are illustrated in our spectroscopic study of the archetype molecular compound 3,4,9,10-perylineteracarboxylic dianhydride. Through our discussion of exciton self-trapping, line broadening, diffusion, and inter-level transitions in this archetype molecular organic crystal, we access a rich array of excitonic processes.; The exciton-interface interaction influences the luminescence and photogeneration efficiency, energy quenching, exciton quantum confinement, and exciton lifetime. After examining these phenomena, we tailor our molecular organic structures to demonstrate photovoltaic cells and efficient organic light emitting devices (OLEDs). We demonstrate transparent OLEDs that can be used in lightweight, conformable, head-up displays, and inverted OLEDs that can be integrated with conventional electronics. We also demonstrate a stacked OLED that integrates three transparent OLEDs to generate a color-tunable, true color device.; Bright and efficient electroluminescence (EL) is a general property of many organic thin films. It is generated by radiative recombination of an exciton formed by electrically injected carriers. We investigate the formation of excitons in the EL process by analyzing our measurements in terms of trap-limited conduction in amorphous materials. We infer that the traps are due to molecular polarons, which also determine the energy distribution of excitons, and hence the EL emission spectrum. We also show that spectral emission can be modified when the luminescent center is in the vicinity of a strong electric dipole, where by adjusting the strength of the dipole field the EL spectrum can be altered.; The radiative recombination of Frenkel excitons in luminescent devices is also influenced by the presence of multilayer structures which introduce microcavity effects. We develop a comprehensive theoretical description of microcavity effects in OLEDs which accounts for the spectral shape and intensity as a function of the emission angle, treating both radiative and waveguided modes. We finally show that optically excited organic material in a microcavity can undergo population inversion and lase. |
