Risultati finali Organic light-emitting field-effect transistors Organic light-emitting field-effect transistor Organic light-emitting field-effect transistors have been demonstrated for the first time. The devices were fabricated by vacuum deposition of tetracene on Si/SiO2 substrates with pre-structured gold source and drain electrodes. Despite the fact that gold electrodes should only form good hole injecting contacts with tetracene, electron injection occurred. The existence of electrons and holes in the transistor channel was proven first by the existence of light emission and second by the typical tetracene electroluminescence spectrum measured during operation of the transistor. The emission was observed close to the drain contact. Despite that, ambipolar behaviour was not observed for these devices, which therefore has to be attributed to a significantly lower electron mobility, especially since electron and hole injection barriers were found to be comparable by UPS studies. In order to attain similar electron and hole mobilities interface doping (electrochemical doping in this case) was performed. Ambipolar operation and luminescence at voltages below 10V could be attained. All-plastic light-emitting field-effect transistors Organic Light-Emitting (Field-Effect) Transistors (LETs) have been fabricated on a flexible and transparent plastic foil (Mylar), acting both as substrate and gate dielectric. The foil is patterned on one side with bottom-contact gold source and drain electrodes, whilst a thin film of gold is evaporated on the opposite side of the foil to form the gate electrode. A vacuum sublimed tetracene film is employed as active layer for charge transport and light emission. The transistor shows unipolar p-type behaviour with mobilities typically of 5·10-4cm2/Vs. Drain-source current and electroluminescence has been simultaneously measured. Provided a suitable gate bias is applied, light emission occurs at drainsource voltages (Vds) above saturation. LETs on plastic substrates could open the way to flexible devices combining the switching function of a transistor and the light emission. Taking advantage of the Ultra-Violet and Visible transparency of the dielectric sheet, attractive developments of the device structure can be envisaged. Indeed, transparent or semi-transparent gate electrode would allow light collection from both sides of the film. Alternatively, a highly reflective metal deposited as gate electrode on one side of the sheet would optimise light extraction from the opposite side. Novel light-emitting organic dyes Novel highly luminescent, thermally and photochemically stable dyes have been prepared and fully characterized by the state of the art of molecular chemistry. Exceptional redox and optical properties such as high absorption, high quantum yield and efficient electroluminescence could be generated by these dyes in special molecular devices. The optical features can be tuned over a large range of wavelengths (about 500 to 850nm). Some of these novel molecules could be used to detect specific targets such as cautions, protons, and biological materials. A special vertical device allows producing OLEDs in which these dyes were used as dopand allowing very efficient exciton and/or energy transfer processes. All these compounds could be produced pure at the gramm scale using home made experimental procedures Ambipolar organic light-emitting field-effect transistors We demonstrate an organic light-emitting field-effect transistor (OLET) with pronounced ambipolar current characteristics. The ambipolar transport layer is a coevaporated thin film of a-quinquethiophene (a-5T) as hole-transport material and N,N'-ditridecylperylene- 3,4,9,10-tetracarboxylic diimide (P13) as electron-transport material. The light intensity is controlled by both the drainsource voltage VDS and the gate voltage VG. Moreover, the latter can be used to adjust the charge-carrier balance. The device structure serves as a model system for ambipolar light-emitting OFETs and demonstrates the general concept of adjusting electron and hole mobilities by co-evaporation of two different organic semiconductors. Ambipolar field-effect organic transistors based on heterostructures For both, the fabrication of complementary logic and for light-emitting devices, ambipolar transport in field-effect transistors is a prerequisite. Ambipolar organic field-effect transistors have been demonstrated based on bilayer heterostructures. The devices are fabricated using pentacene/ perylene-derivative or pentathiophene/ perylene-derivative bilayers. Source and drain contacts are fabricated of two different metals with high and low work function, namely Au and Mg, in order to achieve efficient hole and electron injection, respectively. Pronounced ambipolar transistor characteristics are observed over a large range of bias voltage. The electron and hole mobility in case of pentacene/ perylene-derivative is 1.2x10-2 cm2/Vs and 2x10-4 cm2/Vs, respectively. From pentathiophene/ perylene-derivative bilayer OFETs, an electron and hole mobility of 4x10-4 cm2/Vs and 1.5x10-3 cm2/Vs, respectively, could be extracted. However, no light emission could be observed in these bilayer transistor structures. Advanced optical set up for nanoscale characterization of materials and devices A novel facility to perform nanoscale ultrafast spectroscopy and nanoscale photolithography has been designed and implemented. Single and multiphoton femtosecond excitation coupled to a Laser Scanning Confocal Microscope and photon counting Streak Camera detection allows performing photoluminescence spectroscopy with in-plane spatial resolution of up to 120nm and temporal resolution of 2ps. The facility combines high performance imaging capabilities in 3D with high sensitivity spectroscopic detection of time-resolved photoluminescence (PL). Imaging and spectroscopy are performed on the same spatial position thus allowing a direct correlation of the morphological features with the spectroscopic properties. A direct use of this Optical Nano Probe is in the spectroscopic investigation and imaging of the active areas of molecular electronic and optoelectronic devices such as TFTs, LEDs and PVs cells. Morphology of active layers within working devices can be correlated to field distributions, charge flows, charge recombination and light emission. Nanoscale spectroscopic analyses range from integrated light emission, steady state PL, time resolved PL, one and two photon excited PL, and one and two photon excitation profiles. The new Nanoscale Femtosecond facility sheds light into phenomena, which occurs at the nanoscale and may become an unprecedented tool in the evaluation of organic, hybrid and biological nanostructures and nanodevices. È in corso la ricerca di dati su OpenAIRE... Si è verificato un errore durante la ricerca dei dati su OpenAIRE Nessun risultato disponibile
