This thesis explores new types of perovskite and perovskite-like materials for photovoltaics, with a view towards demonstrating novel and low-cost materials such as metal oxide perovskites for photovoltaics. The first part explores the prototypical organometal halide perovskite CH3NH3Pbl3, where CH3NH3 = methylammonium (MA). MAPbl3 has been studied by the partial replacement of its organic component, MA, with the larger molecule ethylenediammonium (EDA), with the chemical formula NH3(CH2)2NH3. This in turn introduces vacancies into EDA-containing MAPbl3, which has allowed the study of a non-stoichiometric organometal halide perovskite. This work observed that the partial replacement of the MA molecule with a larger molecule reduced the hysteresis. Following this, the low-cost perovskite-like material methylammonium iodo bismuthate has been studied. Methylammonium iodo bismuthate has the chemical formula MA3Bi2lg (MABI), and forms a zero­dimensional network of Bi2lg bioctahedra with quantum confinement. MABI has been characterised and used to fabricate solar cells. This bulk material with an ordered zero-dimensional internal structure exhibits carrier multiplication, and this thesis has demonstrated the fabrication of MABI solar cells. The structure has also been shown to favourably accommodate a small quantity of quantum confined silicon nanocrystals, opening up an avenue of possible hybrid devices which can be explored. Building on this knowledge, this thesis then explores two perovskite oxide materials which have not previously been demonstrated in photovoltaics. Both perovskite oxides exhibit strong and broad visible light absorption which extends into the near-infrared spectrum. One of which, Sr-deficient strontium niobate (Sro.gNb03), exhibits metallic conduction, and has been demonstrated in a photovoltaic cell for the first time. This work demonstrates the possibility of extracting excited carriers in a metal oxide with metallic conduction. The metal oxide perovskite calcium manganite, Ca2Mn2O5, has also been explored for photovoltaics. Ca2Mn2O5 is a plasmonic metal oxide and is therefore highly attractive material for photovoltaics. Solar cells were successfully fabricated using Ca2Mn2O5, and these results demonstrate the possibility of carrier extraction and highlight great opportunities for solar energy harvesting.

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The development of power modules for deployment in hostile environments, where the elevated ambient temperatures demand high temperature capability of the entire converter system, requires innovative power electronic circuits to meet stringent requirements in terms of efficiency, power-density and reliability. To simultaneously meet these conflicting requirements in extreme environment applications is quite challenging. To realise these power modules, the relevant control circuitry also needs to operate at elevated temperatures. The recent advances in silicon carbide devices has allowed the realisation of not just high frequency, high efficiency power converters, but also the power electronic converters that can operate at elevated temperatures, beyond those possible using conventional silicon-based technology. High power-density power converters are key components for power supply systems in applications where space and weight are critical parameters. The demand for higher power density requires the use of high-frequency DC-DC converters to overcome the increase in size and power losses due to the use of transformers. The increase in converter switching frequency reduces the size of passive components whilst increasing the electromagnetic interference (EMI) emissions. A performance comparison of SiC MOSFETs and JFETs in a high-power DC-DC converter to form part of a single phase PV inverter system is presented. The drive design requirements for optimum performance in the energy conversion system are also detailed. The converter was tested under continuous conduction mode at frequencies up to 250 kHz. The converter power efficiency, switch power loss and temperature measurements are then compared with the ultra-high speed CoolMOS switches and SiC diodes. The high voltage, high frequency and high temperature operation capability of the SiC DUTs are also demonstrated. The all SiC converters showed more stable efficiencies of 95.5% and 96% for the switching frequency range for the SiC MOSFET and JFET, respectively. A comparison of radiated noise showed the highest noise signature for the SiC JFET and lowest for the SiC MOSFET. The negative gate voltage requirement of the SiC MOSFET introduces up to 6 dBμV increase in radiated noise, due to the induced current in the high frequency resonant stray loop in the gate drive negative power plane. ii A gate driver is an essential part of any power electronic circuitry to control the switching of the power semiconductor devices. The desire to place the gate driver physically close to the power switches in the converter, leads to the necessity of a temperature resilient PWM generator to control the power electronics module. At elevated temperatures, the ability to control electrical systems will be a key enabler for future technology enhancements. Here an SiC/SOI-based PWM gate driver is proposed and designed using a current source technique to accomplish variable duty-cycle PWM generation. The ring oscillator and constant current source stages use low power normally-on, epitaxial SiC-JFETs fabricated at Newcastle University. The amplification and control stages use enhancement-mode signal SOI MOSFETs. Both SOI MOSFETs will be replaced by future high current SiC-JFETs with only minor modification to the clamp-stage circuit design. In the proposed design, the duty cycle can be varied from 10% to 90%. The PWM generator is then evaluated in a 200 kHz step-up converter which results in a 91% efficiency at 81% duty cycle. High temperature environments are incompatible with standard battery technologies, and so, energy harvesting is a suitable technology when remote monitoring of these extreme environments is performed through the use of wireless sensor nodes. Energy harvesting devices often produce voltages which are unusable directly by electronic loads and so require power management circuits to convert the electrical output to a level which is usable by monitoring electronics and sensors. Therefore a DC-DC step-up converter that can handle low input voltages is required. The first demonstration of a novel self-starting DC-DC converter is reported, to supply power to a wireless sensor node for deployment in high temperature environments. Utilising SiC devices a novel boost converter topology has been realised which is suitable for boosting a low voltage to a level sufficient to power a sensor node at temperatures up to 300 °C. The converter operates in the boundary between continuous and discontinuous mode of operation and has a VCR of 3 at 300 °C. This topology is able to self start and so requires no external control circuitry, making it ideal for energy harvesting applications, where the energy supply may be intermittent.

The grid connected voltage source inverter is now the most widely used interface for connecting renewable power generation to the grid. Control of this device is a key aspect to ensure the performance, reliability and life span of the renewable power generation system. Conventionally, the current control of the grid connected inverter is based on the measured grid side voltage. The power and the power factor at the receiving end, which is usually defined as the point of common coupling, can be controlled accurately. This controller topology has been widely used and many control methods have been developed aiming at objectives such as increasing system stability, decreasing harmonic injection, and improving transient response of the system. However, in case of the voltage measurement is not available, i.e. a faulty voltage sensor, the conventional current control topology will be disabled for lack of information of the grid voltage. This would decrease the reliability and efficiency of the system thus should be improved. voltage-sensor-less In this research, a current control system for the grid connected inverter system not relying on the information provided by the a.c. side voltage sensors will be developed with compliance to the recommendations issued to the performances of the distribution generations such as the harmonic limitations and the fault-ride-through capabilities. Three problem will be addressed and solved. Firstly, the a.c. side voltage should be acquired without the use of a.c. side voltage sensors. This is achieved by adopting an a.c. side voltage estimation algorithm. Secondly, the grid connected inverter should be able to start-up without synchronising to the grid while keep the current injected in a safe range. This is achieved by the newly designed start-up process. Thirdly, the grid connected inverter should be able to ride-through grid faults and providing support to the grid. The transient response of the grid connected inverter is the key measure to define the performance. In this study, a faster symmetrical component decomposition method is proposed to improve the transient response of the current control, without relying on grid voltage sensors. The proposed system is verified by both simulation and experimental tests, with analyses and insight aiming at general applications of the proposed method and algorithms.

Organic semiconductors often make poor ohmic contacts with electrodes due to the deep energy levels forming an energetic barrier at the interfaces between the organic layer and the electrode contact. The mismatch in energy levels at the interface was overcome by inserting PEDOT:PSS material as an anode interlayer for achieving good ohmic contact and selecting single types of charge carriers at the polymer-electrode interface. Despite the significant development that was observed in the OPVs performance, the residual moisture and the acidic nature of PEDOT:PSS can cause degradation of the organic films and therefore affect long term stability. Metal oxides were later suggested as alternative interlayers to the PEDOT:PSS which exhibited high performance and long lifetimes. However, many of the metal oxide studies reported in literature used vacuum deposition methods, such as thermal evaporation and sputter deposition, which are not necessarily desirable for large-scale production. This thesis shows that it is possible to deposit Vanadium oxide (V2Ox) from solution in ambient conditions requiring no post-deposition treatment and achieving comparable efficiency to the most widely used interlayer materials. Using a combination of spectroscopic techniques and device characterisation, it is shown that solutionprocessed V2Ox can be used to replace evaporated metal oxides in optoelectronic devices which are fabricated at high temperatures. The work also goes on to show that it is possible to solution-process nickel oxide from a nickel acetylacetonate precursor and obtain a power conversion efficiency > 5%. Finally, the lifetime study of OPV devices utilising various anode interlayer materials shows that the stability of optimised V2Ox devices can be comparable with other interlayer materials.

One of various ways to curb anthropogenic carbon dioxide (CO2) emissions is by using Li4SiO4 sorbents to capture CO2, which have shown high CO2 uptake capacities (up to 367 mg CO2/g sorbent) at high temperatures (400 to 600 °C). In this study, solid wastes from coal- and biomass-fired boilers that contain high amounts (>47 wt%) of silica were used as precursors in the development of Li4SiO4-based high temperature CO2 sorbents via solid state (SS) and suspended impregnation (SI) methods. Thermogravimetric analyses (TGA) carried out in pure CO2 environment at sorption temperatures of 500 to 700 °C showed the waste-derived Li4SiO4 sorbents have high CO2 sorption capacities (up to 263 mg CO2/g sorbent at 700 °C). This study also experimented for the first time the potential of palm oil mill boiler ash (POMBA) as a waste-derived Li4SiO4 sorbent precursor. It was found that POMBA-derived sorbents showed high CO2 sorption capacities (up to 257 mg CO2/g sorbent at 700 °C in pure CO2 environment). These waste-derived Li4SiO4 sorbents exhibited CO2 sorption capacities exceeding some of those in published work (27 mg CO2/g sorbent). Furthermore, this study analysed the effect of excess lithium on waste-derived sorbents. It was found that depending on the materials used, the amount of excess lithium added during the preparation step affected CO2 sorption performance of the waste-derived sorbents.

Upconversion (UC) for photovoltaics (PV) aims to mitigate the intrinsic losses associated with the transmission of sub-band gap photons. The potential enhancement of a PV device via a coupled UC layer has not been realised experimentally due to the weak absorption coefficient of ~6 cm-1 at 1523 nm across a narrow bandwidth (100 nm) and non-linear nature of the active UC erbium ion (Er3+). These limiting properties have resulted in the characterisation of the UC layer conducted with high power monochromatic lasers at the strongest resonant wavelength which is dissimilar to that of the solar spectrum. Herein, a novel method is developed to determine the photoluminescent quantum yield (iPLQY) of an UC layer under broadband excitation through the correct determination of the absorption spectrum unaffected by re-emission. This method is used to evaluate the iPLQY of the UC material under increasing bandwidths of excitation where saturation is seen for bandwidths greater than 60 nm, significantly shorter than the 100 nm absorption spectrum. Although an iPLQY of 16.2% was achieved, with the normalisation to the solar spectrum this equates to a solar concentration beyond what is attainable on Earth. Therefore, advanced photon management techniques are necessary to realise a working device. An in-depth investigation is conducted on the optimisation of an UC material across a wide range of solar concentrations and doping of the active UC ion which indicates β-NaYF4: 25% Er3+to be the most suitable for a coupled PV device.

Series capacitors are traditionally used in practice to increase the quantity of power transmitted over long transmission lines. This can create potential modes of dynamic instability caused by interactions between synchronous machines and turbine-generator shaft torsional resonance.

The deployment of offshore wind farms (OWFs) has increased in response to the threat of diminishing fossil fuel resources, climate change and the need for security of supply. The cost of offshore wind generation has not reached parity with established forms of electricity production. Operators need to simultaneously decrease the total project costs and increase energy yield to achieve a levelised cost of energy of £100/MWh. However, aspects of the Operations and Maintenance (O&M) remain uncertain, either through stochastic processes or through inexperience in the field. One way to handle uncertainty is to define how much the variance in these aspects affect the cost and availability. The thesis in hand introduces an O&M model and seeks to quantify the effects of uncertain inputs using complex sensitivity analysis methods. The sensitivity analysis is applied to an O&M computer simulation model for offshore wind that was developed prior to this project. Case study OWFs are identified to assess if the important factors are different when projects are comprised of a large number of wind turbine generators (WTGs) and are further offshore from the O&M hub port. The set of cases for the global sensitivity analysis comprises of three projects, to provide information applicable to the industry and demonstrate pertinence of sensitivity analysis on a case by case basis. A screening analysis, using the Morris method, is conducted to identify the most important factors on project cost and availability. This resulted in a list of twenty factors, relating to failure rates; duration of operations and information relating to vessels costs. An in-depth uncertainty analysis is conducted with the important factors to establish their distributions where possible. A global, variance-based sensitivity analysis, using the Sobol’ method, is performed to quantify the effect on the variance of the two outputs. No single factor dominated the effect on O&M cost and availability for all cases. For each case, one to five factors contributed most to output variances. As an example, for a case of 30 WTGs located 20km offshore from the O&M hub port, the output variances are mainly a result of the change of number of crew transfer vessels and heavy lift vessel mobilisation time for nacelle component replacement. For an OWF with more WTGs, further from shore; the availability variance is dominated by more routine repair operations. Moreover, costs are largely dominated by WTG reliability. This work has confirmed that O&M costs are affected by the cost of deploying heavy-lift vessels even though only a small proportion of repairs require them. Significant factors are inconsistent across all the scenarios, supporting the conclusion that sensitivity analysis of each case is a necessary part of O&M costs and availability simulation. Using the most up-to-date information on current O&M practices, the analysis provides an indication of where to focus efforts for O&M cost reduction and improved availability.

Microbial fuel cells (MFCs), which convert organic waste to electricity using microbes, could be used to make the wastewater infrastructure more energy efficient and sustainable. However, the chemical catalysts which catalyse the oxygen reduction reaction (ORR) at the cathode of MFCs are expensive and unsustainable. Mixed community aerobic biocathode biofilms are an alternative to chemical catalysts. However, little is known about the bacteria, their metabolism, and their mechanisms of electron transfer with the electrode. A novel 4-electrode method was used to determine the minimum potential for production of peroxide on a porous carbon felt biocathode support. Biocathodes with a high onset potential for the ORR of +0.4 V vs Ag/AgCl were then cultivated in poised-potential half-cells at working electrode potentials of -0.1 and +0.2 V vs Ag/AgCl. These biofilms show what may be an electrode potential-dependent switch in an electron transfer mechanism from -0.1 to +0.2 V vs Ag/AgCl. The biofilms were dominated by unidentified Gammaproteobacteria, not present in unpolarised controls, which were most likely responsible for the ORR catalysis. This is the first time that a link has been made between a high onset potential for ORR catalysis of +0.4 V vs Ag/AgCl, and the bacteria responsible for this catalysis. Using half-cells, the aerobic biocathodes were enriched and used to replace existing abiotic Pt cathodes in operational MFCs. MFC performance was found to be limited by high external resistance and oxygen mass transfer. The MFC with a biocathode achieved a 9-fold increase in peak power from 7 to 62 W/cm2 using a carbon electrode with a biocathode compared to a plain carbon electrode. A simple battery separator was shown to be as effective as an ion exchange membrane through novel abiotic analysis of this membrane, and the MFC with a battery separator was found to give similar performance to the MFC with an ion exchange membrane.