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Browsing Department of Physics by Author "Kirui, J. K."
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Item Open Access Evaluation of the regression coefficients for South Africa from solar radiation data(2019-09-20) Mulaudzi, Tshimangadzo Sophie; Maluta, N. E.; Kirui, J. K.The knowledge of solar radiation in this dispensation is crucial. The lack of grid lines in the remote rural areas of South Africa necessitates the use of solar energy as an alternative energy resource. Solar radiation data is one of the primary factors considered for the installation of renewable energy devices and they are very useful for solar technology designers and engineers. In some developing countries, estimation of solar radiation becomes a challenge due to the lack of weather data. This scenario is also applicable to South Africa (SA) wherein there are limited weather stations and hence there is a dire need of estimating the global solar radiation data for all climatic regions. Using a five year global solar radiation (𝐻) and bright sunshine (𝑆) data from the Agricultural Research Council (ARC) and South African Weather Service (SAWS) in SA, linear Angstrom – Prescott solar empirical model was used to determine regression coefficients. MATLAB interface was used whereby the linear regression plots were drawn. Annual empirical coefficients of 22 stations were determined and later the provincial values. The range of the regression coefficients, a and b were 0.216 – 0.301 and 0.381 – 0.512 respectively. The 2006 estimated global solar radiation per station in a province calculated from the modified models were compared with the observed and statistically tested. The root mean square errors were less than 0.600 MJm−2day−1 while the correlation relation ranged from 0.782 – 0.986 MJm−2day−1. The results showed the regression coefficients performed well in terms of prediction accuracy.Item Open Access Forecasting Minute Averaged Solar Irradiance Using Machine Learning for Solar Collector Applications(2023-05-19) Nemalili, Ronewa Collen; Jhamba, I.; Kirui, J. K.; Sigauke, C.Challenges in utilising fossil fuels for generating energy call for the use of renewable energy. This study focuses on modelling and forecasting solar energy and optimum tilt angle of solar energy acceptance using historical time series data collected from one of the South African radiometric stations, USAid Venda station in Limpopo province. In the study we carried out a comparative analysis of Random Forest and Bayesian linear regression in short-term forecasting of global horizontal irradiance (GHI). To compare the predictive accuracy of the models, k-Nearest Neighbors (KNN) and Long short-term memory (LSTM) are used as benchmark models. The top two models with the best performances were then used in hourly forecasting of optimum tilt angles for harvesting solar energy. The performance measures such as MAE, MSE, and RMSE were used and the results showed RF to have better performance in forecasting GHI than other models, followed by the LSTM and the third best model was the KNN whereas the BLR was the least performing model. RF and LSTM were then used in modelling and forecasting the tilt angles of optimal solar energy acceptance and as thus, the LSTM outperformed the RF by a small margin.Item Open Access Metal oxide nanostructures and hybrid perovskite semiconductor for photovoltaic application(2020-02) Olaleru, Solomon Alan; Kirui, J. K.; Jhamba, L.; Wamwangi, D.; Roro, K.Perovskite-based solar cells (PSC) is the fastest growing solar technology to date since inception in 2009. This technology has invigorated the photovoltaic (PV) community. While it has taken 15-42 years for traditional PV technologies to achieve maturity, PSC technology has accomplished the same within 10 years. As of late, hybrid perovskite materials have shown incredible possibilities for solar energy conversion and optoelectronics technologies by virtue of its benefits of high conversion efficiency, low-cost preparation and the application of earthabundant materials, which are basic determinants for massive production. The optical properties of lead halide perovskites are of basic significance for almost all applications. Based on the screening from literature, the greater part of reports centred on the fabrication of photovoltaic devices, while the photophysical processes of these materials are missing. In this work, we reported the photophysics of halide perovskites from materials to device. The charge dynamics and charge transport mechanisms were also investigated. At first, we optimized the properties of the perovskite materials before fabrication so as to identify optimal conditions for chemical and material synthesis. These optimal conditions of base perovskite preparations necessitated the use of powder samples to form single phases and also to determine the kinetics and energetics of phase formation. We explored the impact of antisolvent and additive on the photophysical properties and a better understanding of optical response of the perovskite materials. We hold the view that the performance improvement focused on material quality alone without complete understanding of the physics of the carrier-light interaction will not provide adequate solutions to existing problems. We used DMSO as an additive in DMF to regulate the crystal growth by dissolving the residue of PbI2 which can impede the crystallization and ethyl acetate as an anti-solvent to control the morphology of the perovskite film resulting in improved homogeneity. Their impacts on optical properties were examined along with consequent improvement on the light absorption property. Herein, we reported the charge transport mechanism and recombination phenomena in dopantfree HTM perovskite solar cell using I-V and EIS measurement with the focus on physical processes within the perovskite material as an active layer and the parameters that determine the photovoltaic performance. Impedance spectroscopy technique, which reveals the various interfacial processes in terms of resistive and capacitive elements, is used to get an insight into the charge transport through the junction and bulk of the FTO-perovskite solar cell. Again these values were consistent with the results obtained from I-V analysis. These analyses of current– voltage (I–V) characteristics and impedance spectroscopy technique provide essential insights into the performance parameters which determine the transport mechanism and location of electron hole recombination and the efficiency of the device. Perovskite-based solar cells (PSC) is the fastest growing solar technology to date since inception in 2009. This technology has invigorated the photovoltaic (PV) community. While it has taken 15-42 years for traditional PV technologies to achieve maturity, PSC technology has accomplished the same within 10 years. As of late, hybrid perovskite materials have shown incredible possibilities for solar energy conversion and optoelectronics technologies by virtue of its benefits of high conversion efficiency, low-cost preparation and the application of earthabundant materials, which are basic determinants for massive production. The optical properties of lead halide perovskites are of basic significance for almost all applications. Based on the screening from literature, the greater part of reports centred on the fabrication of photovoltaic devices, while the photophysical processes of these materials are missing. In this work, we reported the photophysics of halide perovskites from materials to device. The charge dynamics and charge transport mechanisms were also investigated. At first, we optimized the properties of the perovskite materials before fabrication so as to identify optimal conditions for chemical and material synthesis. These optimal conditions of base perovskite preparations necessitated the use of powder samples to form single phases and also to determine the kinetics and energetics of phase formation. We explored the impact of antisolvent and additive on the photophysical properties and a better understanding of optical response of the perovskite materials. We hold the view that the performance improvement focused on material quality alone without complete understanding of the physics of the carrier-light interaction will not provide adequate solutions to existing problems. We used DMSO as an additive in DMF to regulate the crystal growth by dissolving the residue of PbI2 which can impede the crystallization and ethyl acetate as an anti-solvent to control the morphology of the perovskite film resulting in improved homogeneity. Their impacts on optical properties were examined along with consequent improvement on the light absorption property. Herein, we reported the charge transport mechanism and recombination phenomena in dopantfree HTM perovskite solar cell using I-V and EIS measurement with the focus on physical processes within the perovskite material as an active layer and the parameters that determine the photovoltaic performance. Impedance spectroscopy technique, which reveals the various interfacial processes in terms of resistive and capacitive elements, is used to get an insight into the charge transport through the junction and bulk of the FTO-perovskite solar cell. Again these values were consistent with the results obtained from I-V analysis. These analyses of current– voltage (I–V) characteristics and impedance spectroscopy technique provide essential insights into the performance parameters which determine the transport mechanism and location of electron hole recombination and the efficiency of the device. Perovskite-based solar cells (PSC) is the fastest growing solar technology to date since inception in 2009. This technology has invigorated the photovoltaic (PV) community. While it has taken 15-42 years for traditional PV technologies to achieve maturity, PSC technology has accomplished the same within 10 years. As of late, hybrid perovskite materials have shown incredible possibilities for solar energy conversion and optoelectronics technologies by virtue of its benefits of high conversion efficiency, low-cost preparation and the application of earthabundant materials, which are basic determinants for massive production. The optical properties of lead halide perovskites are of basic significance for almost all applications. Based on the screening from literature, the greater part of reports centred on the fabrication of photovoltaic devices, while the photophysical processes of these materials are missing. In this work, we reported the photophysics of halide perovskites from materials to device. The charge dynamics and charge transport mechanisms were also investigated. At first, we optimized the properties of the perovskite materials before fabrication so as to identify optimal conditions for chemical and material synthesis. These optimal conditions of base perovskite preparations necessitated the use of powder samples to form single phases and also to determine the kinetics and energetics of phase formation. We explored the impact of antisolvent and additive on the photophysical properties and a better understanding of optical response of the perovskite materials. We hold the view that the performance improvement focused on material quality alone without complete understanding of the physics of the carrier-light interaction will not provide adequate solutions to existing problems. We used DMSO as an additive in DMF to regulate the crystal growth by dissolving the residue of PbI2 which can impede the crystallization and ethyl acetate as an anti-solvent to control the morphology of the perovskite film resulting in improved homogeneity. Their impacts on optical properties were examined along with consequent improvement on the light absorption property. Herein, we reported the charge transport mechanism and recombination phenomena in dopantfree HTM perovskite solar cell using I-V and EIS measurement with the focus on physical processes within the perovskite material as an active layer and the parameters that determine the photovoltaic performance. Impedance spectroscopy technique, which reveals the various interfacial processes in terms of resistive and capacitive elements, is used to get an insight into the charge transport through the junction and bulk of the FTO-perovskite solar cell. Again these values were consistent with the results obtained from I-V analysis. These analyses of current– voltage (I–V) characteristics and impedance spectroscopy technique provide essential insights into the performance parameters which determine the transport mechanism and location of electron hole recombination and the efficiency of the device. Perovskite-based solar cells (PSC) is the fastest growing solar technology to date since inception in 2009. This technology has invigorated the photovoltaic (PV) community. While it has taken 15-42 years for traditional PV technologies to achieve maturity, PSC technology has accomplished the same within 10 years. As of late, hybrid perovskite materials have shown incredible possibilities for solar energy conversion and optoelectronics technologies by virtue of its benefits of high conversion efficiency, low-cost preparation and the application of earthabundant materials, which are basic determinants for massive production. The optical properties of lead halide perovskites are of basic significance for almost all applications. Based on the screening from literature, the greater part of reports centred on the fabrication of photovoltaic devices, while the photophysical processes of these materials are missing. In this work, we reported the photophysics of halide perovskites from materials to device. The charge dynamics and charge transport mechanisms were also investigated. At first, we optimized the properties of the perovskite materials before fabrication so as to identify optimal conditions for chemical and material synthesis. These optimal conditions of base perovskite preparations necessitated the use of powder samples to form single phases and also to determine the kinetics and energetics of phase formation. We explored the impact of antisolvent and additive on the photophysical properties and a better understanding of optical response of the perovskite materials. We hold the view that the performance improvement focused on material quality alone without complete understanding of the physics of the carrier-light interaction will not provide adequate solutions to existing problems. We used DMSO as an additive in DMF to regulate the crystal growth by dissolving the residue of PbI2 which can impede the crystallization and ethyl acetate as an anti-solvent to control the morphology of the perovskite film resulting in improved homogeneity. Their impacts on optical properties were examined along with consequent improvement on the light absorption property. Herein, we reported the charge transport mechanism and recombination phenomena in dopantfree HTM perovskite solar cell using I-V and EIS measurement with the focus on physical processes within the perovskite material as an active layer and the parameters that determine the photovoltaic performance. Impedance spectroscopy technique, which reveals the various interfacial processes in terms of resistive and capacitive elements, is used to get an insight into the charge transport through the junction and bulk of the FTO-perovskite solar cell. Again these values were consistent with the results obtained from I-V analysis. These analyses of current– voltage (I–V) characteristics and impedance spectroscopy technique provide essential insights into the performance parameters which determine the transport mechanism and location of electron hole recombination and the efficiency of the device.