Organic Electronics

Hysteresis behaviour of the current–voltage characteristics collected on spin coated synthetic eumelanin layer embedded in the Au/eumelanin/ITO/glass structure is shown. The effect has been observed under dark both in air and vacuum environment and its magnitude has been found related to the eumelanin hydration state. Moreover, in vacuum and under white light illumination, enhancement of the hysteresis loop area respect to those collected under dark has been observed. Space charge storage and charge trapping/detrapping as possible mechanisms responsible of the observed current–voltage behaviour are discussed. Preliminary experimental results have evidenced the possible integration of eumelanin layers in electro-optical charge storage based memory devices.

Boron doped and undoped Poly(vinyl) alcohol/Zirconium-yttrium acetate (PVA/Zr-Y) nanofibers were prepared by electrospinning using PVA as a precursor. The effect of boron doping was investigated in terms of solution properties, morphological changes and thermal properties. The effect of boron doping on calcined yttria stabilized zirconia (YSZ) fibers were evaluated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy analysis. XRD
analysis revealed varying amounts of monoclinic and tetragonal zirconia present in the undoped fibers calcined at 800oC. The average crystallite sizes of the undoped YSZ were increased from 9.28 to 22.79 nm with calcining temperature increasing from 250 to 800 °C. The crystallite size was enhanced with boron doping. The systematic evolution of morphological features in the spun and the processed fibers were employed by scanning electron microscopy.

The challenge of realizing electronic devices based on organic materials started in the early 70‟s. The discovery and advent of conducting polymers in the 80‟s paved the way to new solution-based process and realization of cheap and flexible electronic devices. Mastering thin films fabrication by evaporation techniques also made possible devices realization with optimal properties and control. Organic electronics is nowadays becoming a mainstream innovative field, with perspectives in solar cells, lightning and cheap electronics. The first industrial products are emerging in our every day‟s life, for example in screens for portable electronics. From another perspective, electrical transport through molecules, or entities of molecular size or thickness, created a growing interest in the research community. The development has been slower, mostly hindered by the technical issue of matching the nm molecular size with the typical 100 nm electrical interconnects sizes. This is illustrated by the scientific literature on the topic, with large fractions of the publications related to theoretical studies and nanofabrication methodologies, leaving aside only a marginal numbers of experimental results reports. The field of molecular electronics has nevertheless matured, and initial high expectations are nowadays moderated by the reality of difficulties in reuniting the molecular and macroscopic worlds. In particular, the scanning probe studies on molecules deposited on surfaces illustrated that stability usually require cryogenic temperatures, and the intrinsic conductivity of the molecules under study can be remarkably modified by the environment, the molecules conformations, and details of its interactions with the substrate. These points illustrate how difficult it is to create molecular devices of reproducible and robust properties. Tackling molecular electronics problems through size reduction of „standard‟ organic electronics systems also have stringent limits. The progress in this field cannot be compared to progress in miniaturization of inorganic silicon-based electronics. The primary technical bottleneck to miniaturization is metal-organic interfaces, which have a large importance for organic devices, and easily become predominant for sub-micrometer sizes. A huge research effort has been dedicated to this problem in the last 15 years, aiming at better for better characterization and understanding of dielectric-organic and metal-organic interfaces joining two materials of very different electronic properties. In the midway between bulk organic electronics and single molecule devices, are molecular electronic devices in the size range of 10-100 nm. This thesis is mostly dedicated to investigate these intermediate size devices. We envision several key advantages: (1) direct top-down nanofabrication tools can be used to fabricate reliable and reproducible interconnects in the 50 – 100 nm size range, (2) we can use bottom up fabrication methodologies to create molecular-based materials of size exceeding a few tens of nanometers, (3) by targeting devices where transport occurs though a significant number of molecules, we get access to average properties, with the advantage of studying more robust and reproducible samples, with expected environmental stability making ambient conditions measurements possible. Our ambition is to convince the reader that this mid-sized devices approach is promising, with high potentials. Our ambition is to provide a solid ground for molecular electronics devices realization, where reliability and results confidence are priorities. This explains why, all along this thesis, a large number of control experiments have been performed. This thesis is essentially articulated in three sections. In the first section (Chapter II), we present our methodology for creating the electrodes circuit, the interconnects, the excitation and measurement environments. Light is used as a trigger or excitation source, illustrating how molecular devices can have controlled properties, making them potential candidates for devices properties beyond those of standard inorganic electronics. For this aim, the setup for electrical measurements is placed in a home built-interconnect setup over an inverted optical microscope where we can apply simultaneous optical-electrical measurements followed by temperature and magnetic field complementary studies. We report the fabrication of lateral electrodes with high aspect ratio (104) separated by a 20-100 nm distance, and using simple optical lithography techniques. These „nanotrenches‟ are our basic top-down tool for interfacing organic materials. The next section (Chapter III) is a proof-of-principle experiment, showing that we can create robust molecular electronics devices. The best experimental confirmation for the occurrence of molecular-type transport relates to the study of „switching‟ molecules. Such systems exhibit a reversible, and possibly hysteretic, modification of their properties under external stimulus. For experimental convenience reasons, aiming at minimizing the risks of experimental artifacts, we use a benchmark molecular system, choosing a photochromic molecular film. These molecules are known to reversibly exhibit a change of conformation (cis↔trans) under light excitations in the UV and blue ranges. We use a microsphere coated with a film of these molecules, and trapped over the nanotrench. The sphere is the intermediate size connector, closing the junction between metallic electrodes through a double molecular layer. While a light induced change of conduction has been shown in a vertical geometry in these molecules, the lateral geometry is unexplored. On-switching molecular films as check system, we provide quantitative success rate in observing electrical transport unambiguously related to molecules properties, reaching a success rate better than 90%. The third section (chapters IV and V) presents the use of our methodology to investigate original new molecular materials. The spincrossover phenomenon, occurring as a collective transition with hysteretic behavior triggered by a change in temperature, pressure or irradiation in transition metal complexes, from paramagnetic high spin state (HS, S=2) to diamagnetic low spin state (LS, S=0) has been studied thoroughly in the literature, and well suites as switching molecular system. The transition is often accompanied by a change in color, dielectric constant and volume of the bulk material. Studies have shown that due to the collective nature of the transition, the hysteresis occurs in an ensemble of molecules and not in single molecules, thus spincrossover nanostructures are ideal candidates for observing the physical change (volume) due to the transition and we aimed to detect this change in their transport properties in chapter IV. We therefore used original spin crossover nanoparticles, of well-characterized spin transition properties, positioned over 100 nm-size gaps. The obtained results do not relate to spin transition, but to other intrinsic properties of the particles (high conductivity and photoconductivity) and confirmed that this geometry and size scale opens a view to novel properties investigation. The other molecular system is designed for supramolecular electronics studies, where the bottom-up fabrication involves the construction of a large molecular architecture, of size matching the nanotrenches widths. We investigate a self-assembled molecular system based on a triarylamine derivative as building block. Light triggers a polymerization of these molecules, through radicals creation in the solution. When this growth procedure is probed between metallic electrodes, a surprising self-fabrication of highly conductive molecular wires parallel to the linesof electric field in the gap is observed. The wires have an ohmic character with conductivity values of 104 S.m-1 combined with an extremely low interface resistance, typically six orders of magnitude lower than conventional polymers, samples exhibit high environmental stability persisting for a long time. This "discovery‟, detailed in chapter V, represents a milestone discovery for organic electronics since it describes the first molecular self-assembly having intrinsic metallic behavior in both bulk and at the metal/organic interface when lowering the temperature down to 1.5 K. Once again we emphasize the importance of the intermediate sized devices in making progress in the field of molecular electronics, by discovering materials with novel intrinsic properties and taking a great step towards lowering the parasitic interface resistance of organic materials with metals using self-fabrication procedures.

A new, extended, fused-ring aromatic Poly(diketopyrrolopyrrole-emeraldicene) Copolymer (PDTDPP-alt-EMD) is presented. Conjugated polymers exhibit a balanced hole and electron mobilities of 0.29 cm2 V−1s−1 and 0.25 cm2 V−1s−1, respectively, when used as a single component active semiconductor in OTFTs.

We report highly efficient red phosphorescent organic light-emitting diodes with a triplet p-i-n single quantum well (QW) structure. This p-i-n single QW structure is realized using p-doped and n-doped wide band-gap hole and electron injection and transporting layers with narrow band-gap host and dopant materials. The maximum current and power efficiencies of 11.1 cd/A and 14.4 lm/W, respectively, are demonstrated by a good carrier confinement effect of QW. Very low driving voltage characteristics of 3.7 ∼ 3.9 V at 1000 cd/m2 are realized by almost no injection barrier with high conductivity configuration in our p-i-n structure.

Pulse oximetry is a ubiquitous non-invasive medical sensing method for measuring pulse rate and arterial blood oxygenation. Conventional pulse oximeters use expensive optoelectronic components that restrict sensing locations to finger tips or ear lobes due to their rigid form and area-scaling complexity. In this work, we report a pulse oximeter sensor based on organic materials, which are compatible with flexible substrates. Green (532 nm) and red (626 nm) organic light-emitting diodes (OLEDs) are used with an organic photodiode (OPD) sensitive at the aforementioned wavelengths. The sensor’s active layers are deposited from solution-processed materials via spin-coating and printing techniques. The all-organic optoelectronic oximeter sensor is interfaced with conventional electronics at 1 kHz and the acquired pulse rate and oxygenation are calibrated and compared with a commercially available oximeter. The organic sensor accurately measures pulse rate and oxygenation with errors of 1% and 2%, respectively.

In this chapter, we reviewed the emerging field of
organic spintronics, emphasizing both on the fundamental
aspects of spin injection, transport, relaxation,
and spin dynamics in hybrid inorganic–organic heterostructures
and organic diode devices, as well as
their potential applications. The fundamental spin
physics in purely organic or inorganic–organic
hybrid devices is interesting and intriguing. New
results are emerging very frequently, which opens
new ways to look at the unresolved issues and also
questioning our understanding of the basic spin
dynamics in these materials and their devices.

Smart polymers nanocomposites are highly accepted for smart electronic devices used for sensor and actuator applications. These nanocomposites are developed using the dielectric polymer with some conducting fillers. The present work deals with the different aspects including the development processmaterial used as the conducting nanocomposites for strain sensing application. However, their strong interaction forces make the mixing steps more difficult than encountered for other kinds of fillers. The crystallinity of the polymer is adhered to by the infiltration of the nanofillers which influences the overall properties of the nanocomposite. A study on the improvement of interfacial bonding between the filler and the polymer is of great significance and importance for determining the physical properties and chemical changes, to enhance the mechanical properties of the strain sensor. Therefore,the exploration of interface linker which is cost-effective is needed to be worked out.

The materials science and engineering related to the fabrication of conducting polymer thin films and the progress in the development of devices integrated with organic transparent electrodes based on conducting polymers for display applications are reviewed. Transparent electrodes are essential components for many display modules. With the evolution of display technologies, conducting polymers are recently emerging as important alternative materials for the fabrication of transparent electrodes. Conducting polymers offer some advantages, such as light weight, low cost, mechanical flexibility and excellent compatibility with plastic substrates for the development of next-generation display technologies and, in particular, are expected to play an important role in the development of flexible display technologies.

This research was funded by, and implemented within, a UK national research organisation, while the author was the KE and Impact Evaluation Manager responsible for assessing impact on a £15m UK government-funded research programme.

This work was also submitted as the authors MBA dissertation which was accepted and awarded in 2009.

ABSTRACT: A methodology and methods ‘toolbox’ is proposed for conducting impact research and assessment from within research programmes. The emphasis is upon how to clarify and assess the wider impacts from the early stages onwards.

The approach explicitly acknowledges, and attempts to address, the known issues and challenges of impact assessment while drawing upon the resources and opportunities available to research managers and researchers within such programmes.

The study has two triangulating foundations. Firstly, it examines the academic literature to help identify and design the pilot methodology and methods. Secondly it trials these in a real programme to both test and improve them.

The study was conducted over one year within one leading UK research organisation, where two research programmes (and around 60 research projects of £15m total value) were being assessed for their impacts. The study draws upon actual impact management experience and reflection, prospective (ex ante) and retrospective (ex post) assessments, participatory contributions from leading researchers undergoing assessment, and consultation with external users. The findings of this study outline the pilot and its first iteration. Recommendations are made for improvement to the methodology and methods.

A subsequent follow-on bid to UK government incorporating the impacts identified from implementing this methodology, successfully led to a further £15m of government funding.

It is expected the pilot methodology and methods will be applicable to other organisations, conducting and funding such research programmes, required to research and assess the wider research impacts.

Although primary focus of implemetation trials was upon research in physical sciences, technology, high-tech engineering, computing/IT, and environment, the wider literature study, the methodology design and justification, the methods proposed and used, and the resulting general recommendations and lessons are expected to apply more broadly to many other research areas, where the impact is to be found more widely in the society, economy, government or public sector or within organizations, policies, professions or the public.

Interest in this work is expected from research programme managers, impact managers and assessors, management consultants advising in this area, and government funding managers, all seeking to embed a developing approach to understand, capture, and enhance wider impact.