Egerton University

We embrace a high-throughput investigation strategy beginning from the electronic structure properties to examine three vanadium-based half Heusler alloys with 18 valence electrons, VRhZ (Z = Ge, Si, and Sn), for thermoelectric application. This work is inspired by expected contrasting electrical transport essentials, particularly high electrical conductivity sigma and high Seebeck coefficient S for attaining enhanced figure of merit (ZT) performance. We employ the electronic fitness function (EFF), which evaluates the magnitude of decoupling sigma and S for high ZT by a distinct band structure. The impact of varying the Fermi level on the power factor, electrical conductivity, and Seebeck coefficient is explored. The effects of exchange correlation are reported by use of the Perdew-Burke-Ernzerhof (PBE) functional in line with the framework of the generalized gradient approximation (GGA), as implemented in the ab initio density functional theory. To rigorously assess the reliability of the GGA-PBE functional, subsequent electronic structure calculations are carried out on the three compounds using the GW approximation. We obtain lattice constants of a0 = 5.79 & Aring;, a0 = 5.76 & Aring;, and a0 = 6.09 & Aring; for VRhGe, VRhSi, and VRhSn, respectively. All materials exhibit ductility as indicated by their values of Cauchy pressure, as well as Poisson's ratio and Pugh's ratio values. The VRhSn machinability index is the highest at 2.2456. The highest hardness is realized in VRhSi, which is at 7.9957 GPa. Based on the Kleinman parameter, bond stretching is negligible in all VRhZ materials. VRhZ spatial dependence plots indicate that all investigated compounds are anisotropic. In this study, dynamic stability is observed in all compounds due to the nonexistence of phonon modes that correspond to imaginary frequencies. The derived electronic energy band structure reveals that all three alloys exhibit semiconductor properties with band gap energies of 0.50, 0.32, and 0.42 eV in VRhGe, VRhSi, and VRhSn, respectively, corresponding to indirect transitions. The maximum values realized for the EFF when T = 1000 K using GW are 0.69 x 10-19W 53 ms-1 3 K-2, 0.66 x 10-19W 53 ms-1 3 K-2, 0.79 x 10-19W 53 ms-1 3 K-2 for VRhGe, VRhSi, and VRhSn, respectively. The observed ZT values at 1000 K using GW are 0.91, 0.99, and 0.99 for VRhGe, VRhSi, and VRhSn, respectively. These results of ZT as well as EFF suggest that VRhZ (Z = Ge, Si, and Sn) compounds are promising high-temperature thermoelectric materials.

This work presents a detailed study of p-SnS/n-CdS heterojunction solar cells with Al-ZnO/i-ZnO window layers, combining simulations with the one-dimensional solar cell capacitance simulator (SCAPS-1D) and impedance spectroscopy for an in-depth investigation of the mechanisms limiting device performance. The effects of key cell parameters, such as absorber layer thickness, doping concentration, series resistance (R s), and operating temperature, were systematically explored, as these factors strongly influence solar cell performance. Optimal efficiency was achieved with a 4 µm SnS absorber layer, resulting in a power conversion efficiency (PCE) of 22.76% and an open-circuit voltage (V oc) of 0.77 V under standard illumination conditions. Although increasing the R s significantly degraded the fill factor (FF) and PCE, V oc and short-current density (J sc) remained largely stable. The utility of complex impedance proved crucial in understanding the underlying physical mechanisms of each parameter (thickness, doping, R s) and temperature, and their influence on overall efficiency. In the 0.1 Hz-1 GHz frequency range, two relaxation processes were revealed: a low-frequency response attributed to bulk recombination at the CdS/SnS interface, and a high-frequency response associated with interfacial polarization within the ZnO layers. Notably, the ZnO/CdS and CdS/SnS interfaces exhibited opposing thermal trends, reflected by the evolution of the relaxation times. The coupling between SCAPS-1D and the dynamic study via impedance spectroscopy highlights the importance of absorber doping, optimized thickness and minimized R s as key parameters for obtaining high-efficiency SnS-based thin-film photovoltaic cells, and provides essential information on the interfacial dynamics and volumetric recombination processes that govern device performance and stability.

Lead-based perovskite solar cells (LPSCs) have emerged as one of the most promising photovoltaic (PV) technologies due to their exceptional high light-harvesting capabilities, tunable bandgap, long carrier diffusion lengths, and impressive power conversion efficiencies (PCEs) exceeding 27%. However, the inherent toxicity and environmental risks of lead present a critical obstacle to their large-scale deployment. Accordingly, this review aims to address the performance–sustainability gap of LPSCs by systematically evaluating recent strategies for lead passivation and recovery that enhance device efficiency while minimizing ecological impact. Using the traditional literature review approach, we synthesize current findings on chemical, physical, and interface-level techniques employed to stabilize or neutralize lead within the perovskite structures. Surface passivation methods, such as molecular chelation, ligand engineering, and two-dimensional (2D) capping layers, are explored in detail, accompanied by relevant reaction mechanisms and schematic illustrations. In parallel, we present experimental lead recovery techniques, including solvent-based extraction, electrochemical separation, solid-state capture, and membrane filtration, supported by process flow diagrams and tabulated reaction pathways. Environmental aspects are critically addressed through life cycle assessments (LCAs), end-of-life (EoL) considerations, and environmental footprint analysis. Circular economy approaches tailored to LPSC technology, such as closed-loop recycling, material recovery systems, and sustainable encapsulation, are also examined. Representative lead-based perovskites, including MAPbI 3 , FAPbBr 3 , and mixed-cation variants are discussed in terms of structure–property relationships and stability. A detailed comparison between lead- and tin-based perovskites is also provided, showcasing their respective efficiencies, stabilities, and environmental trade-offs through comprehensive performance tables. Balancing the high efficiency of LPSCs with environmental responsibility is essential for their commercial viability. This review highlights that strategic lead passivation and recovery not only reduce toxicity but also improve device performance and long-term stability. Going forward, critical focus on material innovation, recycling frameworks, and sustainability assessments is key to the responsible advancement of lead-based PV technologies.

Rapid urbanization has led to increasing structural modification of river catchments through dam construction and concrete-lining of natural channels as flood management measures. These interventions can alter the natural hydrology. This necessitates assessment of their influence on hydrology at a catchment scale. However, such evaluations are particularly challenging in data-scarce regions such as the Chongwe River Catchment, where hydrometric records capturing conditions before and after structural modifications are limited. Therefore, we applied a 2D rain-on-grid approach in HEC-RAS to evaluate changes in high-flow responses to short-duration, high-intensity rainfall events in the Chongwe River Catchment in Zambia, where structural interventions have been implemented. The terrain was modified in HEC-RAS to represent 21 km of concrete drains and ten dams. Sensitivity analysis conducted on five key model parameters showed that parameters controlling surface runoff generation, particularly curve number, exerted the strongest influence on simulated peak flows, while routing-related parameters had a secondary effect. Model calibration and validation showed strong performance with R2 = 0.99, NSE = 0.75 and PBIAS = −0.68% during calibration and R2 = 0.95, NSE = 0.75, PBIAS = −2.49% during validation. Four scenarios were simulated to determine the hydrological effects of channel concrete-lining and dams. The results showed that concrete-lining of natural channels in the urban area increased high flows at the main outlet by approximately 4.6%, generated localized instantaneous maximum channel velocities of up to 20 m/s, increased flood depths by up to 11%, decreased lag times and expanded flood inundation widths by up to 15%. The existing dams reduced peak flows by about 28%, increased lag times, reduced flood depths by about 11%, and reduced flood inundation widths by up to 8% across the catchment. The findings demonstrate that enhancing stormwater conveyance through concrete-lining must be complemented by storage to manage high flows, while future work should explore nature-based solutions to reduce channel velocities and improve sustainable flood mitigation. Therefore, the study provides event-scale insights to support flood-risk management and infrastructure planning in rapidly urbanizing, data-scarce catchments.