Innovative solutions and applications for polymer light-emitting diodes

This work focuses on the development of new technical solutions for polymer light-emitting diodes (PLEDs). Treatments were developed to use innovative materials, such as graphene and carbon nanotubes, as hole-transporting layers and surface modifiers on top of ITO. A processing treatment for the preparation of the polymeric emissive layer of PLEDs was also investigated which allowed the improvement of the on/off switching speed of the devices thus enabling their employment in novel applications for visible light communications. Graphene-based transparent thin films obtained via the exfoliation of graphite in the liquid phase were produced with a view of using them as surface modifiers of indium tin oxide (ITO) or as transparent electrodes in organic optoelectronic devices. As-deposited films are relatively resistive, but the sheet resistance was decreased by up to three orders of magnitude by thermal treatment down to values of 10E5 Ohm/square . The films were also chemically doped via the physisorption of the electron-withdrawing molecule (CF3SO2)2NH. This resulted in an increase of the work function by up to 0.5 eV , to yield a value of 5.3 eV comparable to what can be achieved with poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). Thin films of liquid-phase exfoliated graphene and sorted single-walled carbon nanotubes (SWNTs) were deposited on thin ITO layers ( 100 nm). The work function values of these films measured in air using the Kelvin probe were compared with the work function values measured via electroabsorption when the film is inside a device and in contact with the emissive polymer of the device’s active layer. The data shows that the latter appear to be 0.1/0.2 eV higher than those measured in air, whereas this difference is not present for ITO alone. This suggests a charge transfer at the interface of graphene films with the polymer layer. Finally, the thermal processing of the active layer of PLEDs was reported to increase the on/off speed of encapsulated devices by more than double to reach a cut-off frequency of approximately 260 kHz. The underlying mechanism was investigated. Unexpectedly, the increased speed of the device corresponds to the formation of crystalline domains that decrease the thin-film transistor mobility. The data suggest suggests an increase in the charge injection inside the active layer via a trap-assisted injection mechanism. Thanks to such optimisation processing a maximum data rate up to 55 Mbit/s can be envisaged by employing wavelength multiplexing with a high-performance artificial neural network (ANN) equalizer [1]

Organic Visible Light Communications: Methods to Achieve 10 Mb/s

In this review, we summarise methods towards achieving 10 Mb/s connectivity for visible light communications links utilising organic polymer based light-emitting diodes as the transmitter. We present two different methods; on-off keying supported by least mean squares equalisation and orthogonal frequency division multiplexing without equalisation

10 Mb/s visible light transmission system using a polymer light-emitting diode with orthogonal frequency division multiplexing

We present a newly designed polymer light-emitting diode with a bandwidth of ∼350 kHz for high-speed visible light communications. Using this new polymer light-emitting diode as a transmitter, we have achieved a record transmission speed of 10 Mb/s for a polymer light-emitting diode-based optical communication system with an orthogonal frequency division multiplexing technique, matching the performance of single carrier formats using multitap equalization. For achieving such a high data-rate, a power pre-emphasis technique was adopted

A 10 Mb/s visible light communication system using a low bandwidth polymer light-emitting diode

In this paper we experimentally demonstrate a 10 Mb/s error free visible light communications (VLC) system using polymer light-emitting diodes (PLEDs) for the first time. The PLED under test is a blue emitter with ∼600 kHz bandwidth. Having such a low bandwidth means the introduction of an intersymbol interference (ISI) induced penalty at higher transmission speeds and thus the requirement for an equalizer. In this work we improve on previous literature by implementing a decision feedback equalizer, rather than a linear equalizer. Considering 7% and 20% forward error correction codes, transmission speeds up to ∼12 Mb/s can be supported

Claudio Claudiano: De consulatu Stilichonis liber tertius : introduzione, testo, traduzione e commento

Dottorato di ricerca in Scienze letterarie, retorica e tecniche dell'interpretazione, XIX ciclo. A.a. 2006-2007Università della Calabria, Dipartimneto di filologi