Modifying the organic/electrode interface in Organic Solar Cells (OSCs) and improving the efficiency of solution-processed phosphorescent Organic Light-Emitting Diodes (OLEDs)

Organic semiconductors devices, such as, organic solar cells (OSCs), organic light-emitting diodes (OLEDs) and organic field-effect transistors (OFETs) have drawn increasing interest in recent decades. As organic materials are flexible, light weight, and potentially low-cost, organic semiconductor devices are considered to be an alternative to their inorganic counterparts. This dissertation will focus mainly on OSCs and OLEDs. As a clean and renewable energy source, the development of OSCs is very promising. Cells with 9.2% power conversion efficiency (PCE) were reported this year, compared to \u3c 8% two years ago. OSCs belong to the so-called third generation solar cells and are still under development. While OLEDs are a more mature and better studied field, with commercial products already launched in the market, there are still several key issues: (1) the cost of OSCs/OLEDs is still high, largely due to the costly manufacturing processes; (2) the efficiency of OSCs/OLEDs needs to be improved; (3) the lifetime of OSCs/OLEDs is not sufficient compared to their inorganic counterparts; (4) the physics models of the behavior of the devices are not satisfactory. All these limitations invoke the demand for new organic materials, improved device architectures, low-cost fabrication methods, and better understanding of device physics. For OSCs, we attempted to improve the PCE by modifying the interlayer between active layer/metal. We found that ethylene glycol (EG) treated poly(3,4-ethylenedioxy-thiophene):polystyrenesulfonate (PEDOT: PSS) improves hole collection at the metal/polymer interface, furthermore it also affects the growth of the poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) blends, making the phase segregation more favorable for charge collection. We then studied organic/inorganic tandem cells. We also investigated the effect of a thin LiF layer on the hole-collection of copper phthalocyanine (CuPc)/C70-based small molecular OSCs. A thin LiF layer serves typically as the electron injection layer in OLEDs and electron collection interlayer in the OSCs. However, several reports showed that it can also assist in hole-injection in OLEDs. Here we first demonstrate that it assists hole-collection in OSCs, which is more obvious after air-plasma treatment, and explore this intriguing dual role. For OLEDs, we focus on solution processing methods to fabricate highly efficient phosphorescent OLEDs. First, we investigated OLEDs with a polymer host matrix, and enhanced charge injection by adding hole- and electron-transport materials into the system. We also applied a hole-blocking and electron-transport material to prevent luminescence quenching by the cathode. Finally, we substituted the polymer host by a small molecule, to achieve more efficient solution processed small molecular OLEDs (SMOLEDs); this approach is cost-effective in comparison to the more common vacuum thermal evaporation. All these studies help us to better understand the underlying relationship between the organic semiconductor materials and the OSCs and OLEDs\u27 performance and will subsequently assist in further enhancing the efficiencies of OSCs and OLEDs. With better efficiency and longer lifetime, the OSCs and OLEDs will be competitive with their inorganic counterparts

Studies Towards a pH-Sensitive Anticancer Prodrug Model

Tumour-activated prodrug (TAP) is designed to aim at increasing the prodrug selectivity to kill cancer cells. One strategy to is to design a TAP containing an amine cytotoxin, present as an amide function, which could be released more rapidly in the low pH environment of tumour tissues when amide undergoes hydrolysis. The prodrug model (1) was the subject of the current study. At lower pH its un-ionised carboxylic acid group provides neighbouring catalysis of hydrolysis of the adjacent amide. It was synthesised via ring-opening of the imide (2) which itself was directly synthesised from endo-bicyclo[2.2.2]octa-5-ene-2,3-dicarboxylic anhydride and p-methoxyaniline. The pH-rate profile of (1) was established over the pH range of 3-10, covering rapid hydrolysis of un-ionised acid-amide at lower pH but slower imide formation above pH 8 from the ionised acid-amide. From the kinetic data were calculated the dissociation constant for (1) (pKa: 5.1 at 30 C) and limiting lower pH rate constant for hydrolysis of (1) in its fully neutral form (klim: 0.44 min-1 at 30 C). The data in the pH range of 8-10 provided klow (0.067 min-1) representing formation of (2) from fully ionised (1). The following equilibrium reaction was also investigated at high pH, at which (1) was in its fully ionised amide carboxylate form, by kinetic studies on (2) in hydroxide solutions. Imide + OH- Amide carboxylate The second order rate constant for the forward reaction, kf, was 74 L mol-1 min-1 which with klow for the reverse reaction gave K as 1100 L mol-1

Local Non-Hermitian Hamiltonian Formalism for Dissipative Fermionic Systems and Loss-Induced Population Increase in Fermi Superfluids

Non-Hermitian Hamiltonian (NHH) is an effective formalism for open quantum systems. In common wisdom, when the system is described by the Lindblad master equation, the NHH obtained by neglecting its jump term is believed to be a good approximation for a timescale sufficiently shorter than the inverse of the dissipation rate. We challenge this common wisdom and develop a scheme to obtain an appropriate NHH from the original master equation for dissipative fermionic systems. This NHH, called the local NHH, describes the loss process in each individual mode locally. As a concrete example, we justify our new scheme using fermionic superfluid under one-body loss. Furthermore, we find loss-induced population increase in the long time evolution due to the dissipation-induced phase locking between the pairing gap and the anomalous field

Sensitivity study of the charged lepton flavor violating process τ→γμ\tau \to \gamma \mu at STCF

A sensitivity study for the search for the charged lepton flavor violating process $\tau \to \gamma\mu$ at the Super $\tau$-Charm Facility is performed with a fast simulation. With the expected performance of the current detector design and an integrated luminosity of \SI{1}{ab^{-1}} corresponding to one-year of data taking, the sensitivity on the branching fraction (BF) of $\tau \to \gamma\mu$ is estimated to be at the level of \num{e-8}. The sensitivity under different detector performances are also studied. With ideal performance, the BF could be probed to be \num{2.8e-8} at \SI{90}{\percent} confidence level. The sensitivity is expected to scale with the square root of the luminosity, therefore with a total luminosity of \SI{10}{ab^{-1}} corresponding to ten-year of data taking, the sensitivity could reach \num{8.8e-9}, which is about one order of magnitude improvement upon the current best upper limit

Hydrogen Cryosorption of Micro-Structured Carbon Materials

In comparison with the high-pressure adsorption at room temperature, hydrogen adsorption at cryogenic temperatures can be significantly improved at low pressures, which has great potential for prospective mobile applications. In this study, a differential pressure based manometry system was designed and constructed for fast analysing hydrogen adsorption uptakes of sorbents up to a maximum of 10 wt% at 77 K and up to 11 bar. The safety design of the system in compliance with European ATEX directives (Zone 2) for explosive atmospheres was discussed in detail, together with additional pneumatic systems for remote control of the experiments. A thorough error analysis of related experimental tests was also performed. Common carbon sorbents, including several Norit branded activated carbons and graphene nanoplatelets (GNPs) with various surface areas, were characterised for their pore structures. The structural differences among GPNs of different surface areas were also studied. The hydrogen adsorption isotherms of these sorbents, examined in the newly-built manometry system, were further analysed and discussed with reference to the assessed microstructural properties. The carbonisation processes of plasma carbons from the microwave splitting of methane, and biochars from the pyrolysis of Miscanthus, were intensively studied primarily based on Raman spectroscopy, in conjunction with other characterisation techniques such as XRD, FTIR and XPS, for exploring the formation of graphitic structures and crystallinity under various conditions. Two selected types of carbons, the activated carbon AC Norit GSX with a specific surface areas of 875 m2/g and the graphene nanoplates with a specific surface area of 700 m2/g, were decorated with palladium nanoparticles in different compositions. The growth and distribution of doped palladium particles in the carbon substrates were studied, and their effects on porous properties and microstructures of the sorbents were also reviewed. Hydrogen adsorption tests of the decorated carbons were further conducted and discussed, to explore the potential effects of Pd contents on the adsorption kinetics and hydrogen absolute uptakes