Organic Light Emitting Transistors: A Platform for the Integration of Innovative Nanophotonic Structures

The focus of this Ph.D. thesis is the investigation of the opto-electronic performances and photonic characteristics of Organic Light Emitting Transistors (OLETs). These promising multifunctional devices unify the switching properties of transistors with the light emission capability of light-emitting diodes. The OLETs that have been studied in this research present a peculiar trilayer configuration, which can allow to obtain high light emission efficiency by reducing the quenching processes inherent to the device structure. For these devices, the exciton formation, the light outcoupling and the mechanisms responsible for light losses were investigated, aiming at fully disclosing the potentiality of OLETs in therm of External Quantum Efficiency (EQE) and brightness. In addition, the possibility to modulate the width of the emission area by the gate voltage up to extension of the entire channel was demonstrated. This result is of unprecedented importance for allowing the implementation of OLETs in lighting and photonic applications. Furthermore, a novel strategy based on the introduction of a non conventional planar photonic structure into the device architecture was used to increment the light emission efficiency. Indeed, a fully-organic multilayer structure, that worked both as Distributed Bragg Reflector (DBR) and as gate dielectric, was iserted into the OLET architecture to turn the gate dielectric into an optically active component, capable of enhancing light extraction in forward direction by reducing total internal reflections processes. Other unidimensional photonic structures for lasing application were designed, fabricated and characterized. In specific, a linear Distributed Feedback structure (DFB) based on silk was used for realizing a biocompatible, biodegradable and edible organic laser. The entire route for extracting, purifying and manufacturing silk was optimized for achieving the best performing photonic component. Moreover, a method for making optically active silk by feeding directly the larvae with lasing dye molecules was introduced; the method is green because it allows to fabricate intrinsically colored silk by eliminating the need of resources as water, energy and organic solvents. These findings may open perspectives for applications of optically active silk in biophotonics and biological sensors, such as the realization of Lab-on-a- Chip devices for the biodiagnostics.