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Controlling the orientation of the emissive dipole has led to a renaissance of organic light-emitting diode (OLED) research, with external quantum efficiencies (EQEs) of >30% being reported for phosphorescent emitters. These highly efficient OLEDs are generally manufactured using evaporative methods and are comprised of small-molecule heteroleptic phosphorescent iridium(III) complexes blended with a host and additional layers to balance charge injection and transport. Large area OLEDs for lighting and display applications would benefit from low-cost solution processing, provided that high EQEs could be achieved. Here, we show that poly(dendrimer)s consisting of a non-conjugated polymer backbone with iridium(III) complexes forming the cores of first-generation dendrimer side chains can be co-deposited with a host by solution processing to give highly efficient devices. Simple bilayer devices comprising the emissive layer and an electron transport layer gave an EQE of >20% at luminances of up to ≈300 cd/m2, showing that polymer engineering can enable alignment of the emissive dipole of solution-processed phosphorescent materials. Dipole alignment is achieved in efficient solution-processed organic light-emitting diodes featuring a novel poly(dendrimer). A collaborative team led by Paul Burn from the Centre for Organic Photonics & Electronics, School of Chemistry & Molecular Biosciences at The University of Queensland have developed solution-processed organic light-emitting diodes (OLEDs) based on a phosphorescent poly(dendrimer)-based material with an out-coupling efficiency of around 40% and an external quantum efficiency of above 20%. The key to the enhanced light out-coupling in the devices is the favourable alignment of emissive dipoles in the poly(dendrimer), which consists of dendritic side-chains comprised of hole-transporting carbazole-based dendrons and iridium(III) complex-cores. The poly(dendrimer) is blended with a host material to ensure high efficiency in the device. Ultimately, the intelligent design of the developed poly(dendrimers) allowed the authors to utilise a simple bilayer device structure to demonstrate highly efficient solution-processed organic light-emitting diodes.

Solution-processable non-polymeric organic semiconductors are attractive for opto-electronic applications due to their relatively simple synthetic reproducibility and characterization, and enhanced capability for fine-tuning of their properties. We report the synthesis, charge transport, photophysics, and photovoltaic properties of three non-polymeric materials based upon bisarylthiophenyl diketopyrrolopyrrole [DPP(ThAr)2]. The DPP(ThAr)2 molecules are comprised of solubilizing alkyl groups, 2-ethylhexyl (for 1a) and 2-octyldodecyl (for 1b and 2), which are capped with "electron accepting" moieties - fluorenone (1) or benzothiadiazole (2). While the materials could be prepared under standard Suzuki-Miyaura cross-coupling conditions, a simple direct arylation afforded 2 and 1b in good yields. We found 1a with a short alkyl chain lacked sufficient solubility for solution processing but 1b and 2 are solution processable and form good quality films. All three materials exhibited ambipolar charge transport in field effect transistors, with 1b showing balanced charge mobilities of about 10−3 cm2 V−1 s−1. Bulk heterojunction solar cells of 1b or 2 with PC71BM were found to have high open-circuit voltages (up to 0.9 V) with power conversion efficiencies of up to 4.5% and 2.6%, respectively.

We report the synthesis and characterization of a novel thiocarbonyl iso-DPP derivative, namely 1,3,4,6-tetraphenylpyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dithione. Even without solubilising alkyl chains, the small molecule could be processed from organic solvents such as dichloromethane, chloroform or dichlorobenzene, and it was found that the optical properties of neat thin films were strongly dependent on the solvent used. Field effect hole mobilities were of the order 10−4 cm2 V−1 s−1, with mobilities measured in a diode configuration solvent dependent and at least an order of magnitude lower. Importantly, blends of the iso-DPP derivative with PC70BM, a typically used electron acceptor in bulk heterojunction solar cells, were found to possess hole mobilities of up to 10−3 cm2 V−1 s−1 in a diode configuration, which was an order of magnitude larger than the electron mobility. Finally, simple bulk heterojunction solar cells were fabricated with maximum power conversion efficiencies of 2.3%.

Two new heteroleptic Pt(II) complexes bearing an n-hexyloxy substituted phenyllepidine-based ligand and either a picolinate (pic) or acetylacetonate (acac) coligand are synthesized for use in organic light-emitting field-effect transistors (LEFETs). Both compounds are obtained in good yields via a short and straightforward synthetic route. It is found that while both Pt(II) complexes show good chemical stability and solubility, the coligand affects the photoluminescence quantum yield and crystal packing of the complexes. Although aggregate induced phosphorescence enhancement is not observed, it is found that high concentrations of the emitters in a poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] host lead to improved charge injection in hybrid LEFETs. LEFETs with area emission, high ON/OFF ratios (> 10(6)) and mobilities (approximate to 1.3 cm(2) V-1 s(-1)), and external quantum efficiencies of up to 0.1% at the highest brightness of 855 cd m(-2) are demonstrated.

A see-through organic light emitting field-effect transistor (LEFET) is realized by using a highly transparent, high mobility material. Low voltage operated LEFETs with increased optical and electrical characteristics are shown.

Although many nanoscale materials such as quantum dots and metallic nanocrystals exhibit size dependent optical properties, it has been difficult to incorporate them into optical or electronic devices because there are currently no methods for precise, large‐scale deposition of single nanocrystals. Of particular interest is the need to control the orientation of single nanocrystals since the optical properties are usually strongly anisotropic. Here a method based on electrophoretic deposition (EPD) is reported to precisely assemble vertically oriented, single gold nanorods. It is demonstrated that the orientation of gold nanorods during deposition is controlled by the electric dipole moment induced along the rod by the electric field. Dissipative particle dynamics simulations indicate that the magnitude of this dipole moment is dominated by the polarizability of the solution phase electric double layer around the nanorod. The resulting vertical gold nanorod arrays exhibit reflected colors due to selective excitation of the transverse surface plasmon mode. The EPD method allows assembly of arrays with a density of over one million, visually resolvable, vertical nanorods per square millimeter.

The focus on women in physics in Australia has increased substantially since the last report at the International Conference of Women in Physics (ICWIP) in 2014. This is evident in many aspects; however, the number of women studying physics has remained static at levels that are far too low. In addition, many different organizations and groups are actively working on combating stereotype problems in culture as well as supporting women in their professional career path. The outlook for women in physics in Australia is now very promising.

Stimuli-responsive optical etalons are an exciting class of next-generation sensors because they are scalable, cost-effective and offer tunability of their optical response across the entire UV–vis–NIR wavelength range. In this study, double-network cellulose hydrogels are used as a soft, responsive medium and are incorporated into Fabry–Perot optical etalons. The thin cellulose hydrogel layer can be solution processed. The hygroscopic hydrogel undergoes both refractive index and thickness changes in response to changes in humidity. This leads to strong changes in reflection due to optical interference within the metal–insulator–metal (MIM) cavity. The response can be optimized by adjusting the chemical crosslinker ratio. These flexible MIM structures provide a robust platform for optically based chemical sensors.

Display technology is expected to have a market industry value greater than 70 billion US dollars by 2026. Although organic light emitting devices have found their way into the display industry, there is still a need for higher device efficiencies, lower cost materials, and easier, scalable production methods. This drives the need to gain a deeper understanding of organic semiconductors, which can pave the way to these goals. As such, there is undeniable demand for new classes of semiconductor materials, ideally with a high photoluminescence quantum yield, balanced charge transport, and high light out-coupling through dipole engineering. This thesis describes a body of work which specifically addresses the task of independent control over luminescent, transport and processing properties of organic semiconducting materials with dendritic structures. A family of Ir(III) complexes is introduced and studied including dendrimers; poly(dendrimers); and co-polymers. In the first instance, photo-physical and electrical properties of materials are described, before building on this knowledge to develop efficient organic light emitting diodes. The dipole orientation was furthermore studied in these materials as an intrinsic property of with a view to achieving higher out coupling. Finally, moving away from a material-centric approaches and dendritic design, the charge transport and emissive properties of organic semiconductors were simultaneously studied in a heterostructure light-emitting field effect transistor by cryogenic techniques. The main findings from this research were as follows: I) the photophysical properties improved by increasing the number of dendron branches in the dendritic structure. This delivers extra insulating space between the chromophore cores which leads to less concentration quenching; II) combining dendrimers with a polymer backbone was beneficial not only toward improving the film quality but also providing heteroleptic structures which are more likely to contain horizontally oriented emissive dipoles; III) the results of temperature-dependent measurements demonstrated that, as the device was cooled down, the intrinsic hole mobility followed an Arrhenius response with the overall EQE increases. The implications of these findings are toward simplifying the device structures using more efficient devices. This can be achieved by means of highly luminescent materials as well as enhancement in device out coupling, meaning that light can be emitted preferably perpendicular to the device output plane. The fundamental studies also established some ground rules for engineering high radiative efficiencies in light-emitting field effect transistors, which should aid in both material and architecture design for future device iterations. Future work may concentrate on chemically engineering the material structures for better properties as well as control over dipole orientation.

To improve the range resolution in inexpensive conventional long pulse optical time domain reflectometer (OTDR) for application in structural health monitoring (SHM) and robotic neural network, the Fourier Wavelet Regularized Deconvolution (ForWaRD) based on the adaptive wavelet method is employed. Since Deconvolution is a noise sensitive process, employing the (ForWaRD) method enhances the signal to noise ratio. Simulation for long pulse OTDR system is done and ForWaRD method is employed to improve the resolution of the OTDR system to the order of several centimeters. In this method the resolution is limited by the bandwidth of detector, bandwidth of electronic circuit, and the sampling rate of analog to digital convertor.

Area emission is realized in all-solution-processed hybrid light-emitting transistors (HLETs). A new HLET design is presented with increased aperture ratio, and optical and electrical characteristics are shown.

Light-emitting field effect transistors (LEFETs) are a class of organic optoelectronic device capable of simultaneously delivering the electrical switching characteristics of a transistor and the light emission of a diode. We report on the temperature dependence of the charge transport and emissive properties in a model organic heterostructure LEFET system from 300 K to 135 K. We study parameters such as carrier mobility, brightness, and external quantum efficiency (EQE), and observe clear thermally activated behaviour for transport and injection. Overall, the EQE increases with decreasing temperature and conversely the brightness decreases. These contrary effects can be explained by a higher recombination efficiency occurring at lower temperatures, and this insight delivers new knowledge concerning the optimisation of both the transport and emissive properties in LEFETs.

Bulk heterojunction (BHJ) organic solar cells and photodiodes require optimised active layer structures for both charge carrier photo-generation and extraction to occur efficiently. The most efficient polymer:fullerene devices comprising narrow optical gap donor polymers invariably have a high fullerene fraction. In such circumstances photo-generated carrier extraction is compromised, as charge transport is often unbalanced with electron transport in the fullerene dominating. In this current work we study the high efficiency blend system poly(2,5-{2-octyldodecyl}-3,6-diketopyrrolopyrrole-alt-5,5-{2′,5′-di[thien-2-yl]thieno[3,2-b]thiophene}) (DPP–DTT):phenyl-C71-butyric acid methyl ester (PC70BM). We show that by manipulating the packing of the (DPP–DTT) chains, large hole mobilities >0.02 cm2 V−1 s−1 can be obtained in a simple polymer-only diode. More importantly, when blended with PC70BM in a 1 : 3 ratio the hole mobility was found to increase to 0.2 cm2 V−1 s−1. This is the first case of a polymer:fullerene solar cell where the charge carrier transport is limited by the electron mobility of the fullerene rather than the hole mobility of the donor material. Photophysical measurements reveal that the charge generation quantum yield is also enhanced when the DPP–DTT chains are optimally packed. The simultaneous improvement of the charge transport properties and charge generation quantum yield delivers an order of magnitude increase in the power conversion efficiency.

The synthesis of three pyrrolo[3,2-b]pyrrole-1,4-dione (isoDPP) derivatives is described, namely 1,3,4,6-tetraphenylpyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione 2, 1,4-diphenyl-3,6-di(thiophen-2-yl)pyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione 3, and 1,4-bis(4-(hexyloxy)phenyl)-3,6-di(thiophen-2-yl)pyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione 7 in which the molecular structures differ in the aromatic ring (phenyl or thiophene) attached to the nitrogen atom. Thin films of 2, 3, and 7 could be formed by evaporation under vacuum. In the case of 2 and 3 GIWAXS measurements showed that the film structural ordering was similar to that measured in single crystals. In contrast GIWAXS showed that 7 had features associated with liquid crystalline materials. Time dependent density functional theory (TDDFT) calculations predicted that the transition between the lowest energy singlet excitation (S1) and the ground state (S0) would be optically forbidden due to the centrosymmetric geometries of compounds. Photophysical measurements showed that the compounds were weakly luminescent, with low radiative rates in solution of order 106 s−1, which are consistent with the TDDFT predictions. Furthermore, photoinduced absorption (PIA) spectroscopy showed that there is a long-lived low energy state, which has been assigned as a triplet and provides a further non-radiative decay pathway for the excited state.