Patterned Electrode Vertical Organic Field Effect Transistor (PE-VOFET) operational behavior is examined in this
work with the use of self-consistent numerical model and experimental measurements. The device is described as a
single carrier type diode where one of its electrode's electrical properties could be altered under the gate influence,
switching the current regime between the Contact Limited (CL) and the Space Charge Limited (SCL) regimes. Here we
show that two distinct mechanisms can play a role in the switching process; inducing the formation of virtual contacts
for the ideal Schottky barrier-based device or inducing a potential barrier which eliminates charge extraction for the
non-ideal ohmic contact-based device. The latter is further examined by varying the Patterned Electrode (PE) thickness
which alters the sub-threshold swing performances, determining the gate bias required to turn off the device. We
further provide optimization rules regarding the active layer thickness (channel length), which hold for the 'ideal'
performances of the single layer PE-VOFET. Based on the aforementioned models and optimization rules, we provide
guidelines for the ideal PE-VOFET structure and future challenges in its fabrication.
The last decade has seen tremendous advances in the field of semiconducting-polymer optoelectronics as a result of a concerted chemistry, physics and engineering effort. For example, ink-jet-printed full-color active-matrix thin-film display prototypes with semiconducting polymers as the active layers have already been demonstrated. The key advantages of this technology lie in its full-color capability, scalability to both large-area and micro- displays, as well as low-cost associated with simplicity and solution processability. In a number of related inorganic device technologies, the control of optical properties using photonic structures has ben crucial to the performance of the devices. In principle, polymer devices can also benefit from such control if appropriate polymer optical building blocks that retain the processing advantages can be found. Here we will show that the refractive index of poly(p- phenylenevinuylene) (PPV) can be tuned over remarkable ranges from 1.6 to 2.7 at 550-nm wavelength by dispersing 50-angstrom-diameter silica nanoparticles into its matrix. This is achieved without incurring significant optical scattering losses. Using these semiconducting-polymer composites, we have demonstrated efficient distributed Bragg reflectors in the green spectral region from relatively few periods of quarterwave stacks of the high- and low-index materials. Controlled chemical doping of these photonic structures fabricated polymer microcavity light-emitting diodes in which current is injected through the polymer DBR with adequate confinement of photons and electron-hole pairs. We have also fabricated photo pumped all-polymer microcavity structures.
The synthesis and luminescent properties of the homopolymers (4,5) and copolymers (9,10) carrying ion-transporting side chains are reported. When fabricated as alight emitting electrochemical cell the copolymer 10 exhibited a significant reduction in turn-on voltage and improved luminous efficiency compared with a conventionally fabricated polymer light emitting device. Similar results were observed with the pyridine copolymer 13. The model meta-linked trifluoromethyl substituted distyrylbenzene derivative 16 has been synthesized and its crystal structure has been determined with a view to evaluating the related polymers as charge transporting materials.
We present time-resolved and time-integrated measurements of optical gain and its effects in films and microcavities made from poly(p-phenylenevinylene) (PPV). We demonstrate that PPV films yield net gain due to stimulated emission with a lifetime of about 20 ps when excited with 200 fs pulses. The short duration of this gain is shown to result from exciton- exciton annihilation. We present results showing how this gain leads to spectral narrowing of the emission from PPV films and discuss why it is unlikely cooperative phenomena play a role in this phenomenon. We present evidence that it results from waveguiding of amplified spontaneous emission. Newly developed high-finesse microcavities are described, for which it is possible to obtain lasing thresholds below the onset of exciton-exciton annihilation. We present measurements of the far-field emission patterns from these structures and also demonstrate a measurement of the coherence time of their emission.