<p>Thin film photovoltaic materials have garnered much interest recently due to their processability in addition to good properties for conversion of solar photons to usable energy. Amine-thiol chemistry has shown the ability to produce solution processed materials such as Cu₂ZnSn(S,Se)₄ (CZTSSe), a thin film absorber composed of earth abundant metals. Using similar solution processing methods as those used to produce CZTS, we wish to synthesize a phase pure solution processed material from molecular precursors of metals and metal chalcogenides into an Ag₂ZnSnSe₄ absorber which lacks the electronic defects that plague CZTSSe. Additionally, we will utilize the reactive dissolution of metal in amine-thiol solution chemistry for a more detailed understanding of how metal-sulfur complexes form and then decompose into films, to gain insight about the conditions that produce stable solutions and high quality films for a better ability to optimize processing conditions. </p><p><br></p><p>We find we are able to individually dissolve zinc metal, tin metal, and silver sulfide precursors to produce solutions of metal thiolate complexes. Based on results from electrospray ionization mass spectrometry (ESI-MS), proton nuclear magnetic resonance (¹H-NMR), and extended X-ray absorption fine structure (EXAFS)/ X-ray absorption near edge spectra (XANES) we propose that these structures contain thiolate molecules coordinated with Ag, Zn, and Sn in the +1, +2, and +2 oxidation states respectively. However, mixing these produces an AZTS solution which is only stable for 3 hours, due to a redox reaction between Ag⁺ and Sn²⁺ which forms Sn⁴⁺ and insoluble Ag metal. To solve this, we synthesize SnS₂ and show this produces a different Sn-thiolate complex with fully oxidized Sn⁴⁺. This is then used to produce the first stable AZTS solution, an essential step to fabricating reproducible films. We use this AZTS solution to fabricate films containing AZTS, and selenize these films in a tube furnace to produce films which contain AZTSe as well as secondary phases. We then use rapid thermal processing furnace to remove some of these secondary phases, and discuss ways to further improve our material quality.<br></p><p></p>

M.Tech (Department of Electronic Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / Due to the fickle nature of weather upon which renewable energy sources mostly depend, a shift towards a sustainable renewable energy system should be accompanied with a good intermediate energy storage system, such as a battery bank, set up to store the excess supply from renewable sources during their peak periods. The stored energy can later be utilised to supply a regulated and steady power supply for use during the off-peak periods of these renewable energy sources. Battery banks, however, are often faced with the challenge of charge imbalance due to the disparities that occur in the operating characteristics of the batteries that constitute a bank. When a battery bank with charge imbalance is repeatedly used in applications without an effective battery management system (BMS) through active charge equalisation, there could be an early degradation, loss of efficiency and reduction of service life of the entire batteries in the bank. In this research, a universal battery management system (BMS) in stand-alone photovoltaic application was proposed and designed. The BMS consists majorly of a switched capacitor (SC) active charge equaliser, designed with a unique configuration of high capacitance and relatively low switching frequency, which can be applicable to common battery types used in stand-alone photovoltaic application. The circuit was mathematically optimised to minimise losses attributed to impulsive charging and tested with lead acid, silver calcium, lead calcium and lithium ion batteries being commonly used in stand-alone photovoltaic application. The SC design was verified by comparing its simulation results to the digital oscilloscope results, and with both results showing similar values and graphs, the design configuration was validated. The design introduced a simple control strategy and less complicated circuit configuration process, which can allow an easy setup for local usage. The benefit of its multiple usage with different stand-alone photovoltaic battery types saves the cost of purchasing a different charger and balancer for different battery types. More so, the design is solar energy dependent. This could provide an additional benefit for usage in areas where energy dependence is off-grid.