12 research outputs found
Robust Arduino controlled spin coater using a novel and simple gravity chuck design
No full textSpin coaters offer an invaluable method of thin film fabrication. Various implementations, both proprietary and open-source exist, offering vacuum and gravity samples chucks. These implementations vary in their reliability, ease-of-use, cost, and versatility. Here we present a novel easy-to-use open-source gravity-chuck type spin coater with minimal points of failure at a material cost of around 100 USD (1500 ZAR). The unique chuck design makes use of interchangeable brass plate sample masks, each specific to a sample size, these can be made with basic skills and common hand tools. In comparison, replacement chucks for commercial alternatives can cost as much as the entire spin coater we present. Open-source hardware such as this provides an example for individuals in the field on the design and development of hardware where reliability, cost, and flexibility are most important, as is the case for many institutions in developing countries
Robust Arduino controlled spin coater using a novel and simple gravity chuck design
No full textSpin coaters offer an invaluable method of thin film fabrication. Various implementations, both proprietary and open-source exist, offering vacuum and gravity samples chucks. These implementations vary in their reliability, ease-of-use, cost, and versatility. Here we present a novel easy-to-use open-source gravity-chuck type spin coater with minimal points of failure at a material cost of around 100 USD (1500 ZAR). The unique chuck design makes use of interchangeable brass plate sample masks, each specific to a sample size, these can be made with basic skills and common hand tools. In comparison, replacement chucks for commercial alternatives can cost as much as the entire spin coater we present. Open-source hardware such as this provides an example for individuals in the field on the design and development of hardware where reliability, cost, and flexibility are most important, as is the case for many institutions in developing countries
Property correlations in materials for energy applications utilising advanced X-ray and photophysical techniques
No full textA thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, School of Chemistry, University of the Witwatersrand, Johannesburg, 2023Hybrid-perovskites are an emerging material class, with optoelectronic properties highly suited for photovoltaics (PV), light emitting diode, and phosphor applications. Among PVs they have seen a meteoric rise in photon conversion efficiency (PCE) over the last decade, exceeding that of thin-film and multi-crystallite Si PV. Despite the rapid evolution of PCE within these materials, environmental and thermal stability remain the major impediment for their commercial viability. The use of A site cation substitution is an approach to enhance performance and stability in the versatile family of hybrid perovskites.
In this thesis, the effect of A site cation substitution on the phase transitions and stability is explored, for both cations which appropriate for the APbX3 structure, and a larger organo-ammonium cation (A′ ) associated with the formation of lower dimensionality hybrid perovskite derivative structures. Both approaches are reported in literature to provide exceptional stability and PV PCE improvements.
The hybrid perovskite (F AP bI3)0.85(MAP bBr3)0.15 was characterised using in-situ variable-temperature X-ray diffraction (VT-XRD) data. Sequential Rietveld refinements were employed to explore phase stability, and structural characteristics of this data (FA = formamidinium, MA = methylammonium). A more gradual α → β phase transition is identified, compared to the single cation systems in literature. The effect of Caesium (Cs) substitution on (F AP bI3)0.85(MAP bBr3)0.15 has been characterised across a series of VT-XRD measurements through parametric Rietveld refinement. The introduction of Cs is correlated to divergence between the observed onset temperatures for the cubic to tetragonal and a 0a 0a 0 to a 0a 0 c + (Glazer notation) transitions in the systems, which occur for the α/β phase transition. Beyond the performance improvements, the inclusion of larger A′ cations, have been associated with structural defect passivation, and electronic property tuning due to quantum confinement effects in perovskite derived structures.
Hybrid perovskite based systems containing the A′ cation, propylammonium are studied to gain insights on phase stability and phase formation, and optical properties in these systems. The phase composition, structural III properties, and optical properties of (PABr)2x(MABr)1−xPbBr2, 0 ≤ x ≤ 1 and P ABr/MAP bBr3 systems were studied using ex-situ XRD, optical absorbance spectroscopy and photoluminescence measurements (PA = propylammonium). These systems were fabricated by spin coating, with the former from a single well mixed precursor solution and latter a 2-stage process, where PABr was added in various concentrations to a fully formed MAPbBr3 film. Mixed phase compositions were formed of (P A)2MAn−1P bBr3n+1 2- dimensional (2D) and quasi-2D hybrid-perovskite derivative phases, where n determines the layer thickness and n = ∞ is a MAPbBr3 phase. The difference in the kinetic and thermodynamic aspects of film formation in these systems was leveraged to propose a set of controlling factors responsible for the phase formation behaviour of the varied formation conditions.National Research Foundation (NRF)
University of the WitwatersrandTL (2024
Property and structural characterisation of Fe and FeNi bonded NbC cermets for high temperature wear applications
No full textThe effect of sputtered Pt40Pd57Al3 thin film thickness on SO2(aq) electro-oxidation
No full textThe influence of sputtered Pt40Pd57Al3 thin films of varying thickness, in the as-deposited (AD) and annealed (AN) state, was investigated for the electro-oxidation of aqueous SO2. From physical characterisation (scanning electron microscopy (SEM) and grazing incidence X-ray diffraction (GIXRD)), significant differences were found in the morphology and crystallinity between AD and AN samples. In terms of electrochemical activity, the current output for the AD and AN thin films decreased as the thickness increased, whilst the AN thin films in general resulted in lower current outputs. No specific trend was observed for stability in an acidic environment and a 60 nm Pt40Pd57Al3 thin film proved to be the optimum thickness for aqueous SO2 electro-oxidation. In addition, the 60 nm Pt40Pd57Al3 AN thin film outperformed pure Pt (60 nm, AD and AN) in terms of current density and stability, emphasising the fact that multicomponent electrocatalysts can be superior compared with their pure metal counterpart
Elucidating the Trajectory of the Charge Transfer Mechanism and Recombination Process of Hybrid Perovskite Solar Cells
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Elucidating the Trajectory of the Charge Transfer Mechanism and Recombination Process of Hybrid Perovskite Solar Cells
No full textPerovskite-based solar cells (PSCs) have attracted attraction in the photovoltaic community since their inception in 2009. To optimize the performance of hybrid perovskite cells, a primary and crucial strategy is to unravel the dominant charge transport mechanisms and interfacial properties of the contact materials. This study focused on the charge transfer process and interfacial recombination within the n–i–p architecture of solar cell devices. The motivation for this paper was to investigate the impacts of recombination mechanisms that exist within the interface in order to quantify their effects on the cell performance and stability. To achieve our objectives, we firstly provided a rationale for the photoluminescence and UV-Vis measurements on perovskite thin film to allow for disentangling of different recombination pathways. Secondly, we used the ideality factor and impedance spectroscopy measurements to investigate the recombination mechanisms in the device. Our findings suggest that charge loss in PSCs is dependent mainly on the configuration of the cells and layer morphology, and hardly on the material preparation of the perovskite itself. This was deduced from individual analyses of the perovskite film and device, which suggest that major recombination most likely occur at the interface
Correlating phase behavior with photophysical properties in mixed‐cation mixed‐halide perovskite thin films
No full textMixed cation perovskites currently achieve very promising efficiency and operational stability when used as the active semiconductor in thin‐film photovoltaic devices. However, an in‐depth understanding of the structural and photophysical properties that drive this enhanced performance is still lacking. Here the prototypical mixed‐cation mixed‐halide perovskite (FAPbI3)0.85(MAPbBr3)0.15 is explored, and temperature‐dependent X‐ray diffraction measurements that are correlated with steady state and time‐resolved photoluminescence data are presented. The measurements indicate that this material adopts a pseudocubic perovskite α phase at room temperature, with a transition to a pseudotetragonal β phase occurring at ≈260 K. It is found that the temperature dependence of the radiative recombination rates correlates with temperature‐dependent changes in the structural configuration, and observed phase transitions also mark changes in the gradient of the optical bandgap. The work illustrates that temperature‐dependent changes in the perovskite crystal structure alter the charge carrier recombination processes and photoluminescence properties within such hybrid organic–inorganic materials. The findings have significant implications for photovoltaic performance at different operating temperatures, as well as providing new insight on the effect of alloying cations and halides on the phase behavior of hybrid perovskite materials
