Improving the Conversion Ratio of QDSCs via the Passivation Effects of NiS.

To revolutionize the photochemical efficiency of quantum dots sensitized solar cells (QDSSCs) devices, herein, a passivation of the cells with multilayer material has been developed for heterojunctions TiO2/NiS/MnS/HI-30/Pt devices. In this study, NiS and MnS were deposited on a photoanode for the first time as passivated photon absorbers at room temperature. The adoption of NiS as a passisvative layer could tailor the active surface area and improve the photochemical properties of the newly modified cells. The vibrational shifts obtained from the Raman spectra imply that the energy change is influenced by the surface effect, giving rise to better electronic conductivity. The electrochemical stability and durability test for the N/M-3 device slows down and remains at 8.88% of its initial current after 3500 s, as compared to the N/M-1 device at 7.20%. The disparity in charge recombination implies that both the outer and inner parts of the nanoporous material are involved in the photogeneration reaction. The hybridized N/M-3 cell device reveals the highest current density with a low potential onset, indicating that power conversion occurs more easily because photons tend to be adsorbed easily on the surface of the MnS. The Nyquist plot for N/M-1 and N/M-3 promotes the faster transport of electrolytic ions across the TiO2/NiS/MnS, providing a good interaction for the electrolyte. The I-J Value of 9.94% shows that the passivation with the NiS layer promotes electron transport and enhances the performance of the modified cells. The passivation of the TiO2 layer with NiS attains a better power conversion efficiency among the scant studies so far on the surface passivation of QDSCs.

Graphene oxide:Fe2O3 nanocomposites for photodetector applications: experimental and ab initio density functional theory study.

In this report, a GO:Fe2O3 nanocomposite was synthesized using a one-step covalent attachment approach using a sol-gel technique. The optical absorbance, photoconductive, photo-capacitive, and electrical properties were obtained using spectroscopy, and current-voltage (I-V) measurements. An enhanced optical absorbance with corresponding band gap reduction is observed when Fe2O3 nanoparticles are incorporated in GO. A corresponding enhanced photoconductance in the order of ×101 was observed due to the impact of band gap narrowing. The enhanced photoconductivity and photo-capacitance can be attributed to energy and charge transfer between GO and Fe atoms, leading to the generation of photo-induced excitons. Density function theory calculations indicate increased charge transfer when GO is doped with Fe-O atoms, which is consistent with experimental data. The observed results could potentially enable the use of GO:Fe2O3 nanocomposites for photodetectors and other optoelectronic applications.

FeS/FeS2 nanoscale structures synthesized in one step from Fe(ll) dithiocarbamate complexes as a single source precursor.

Nanoscale FeS and FeS2 mixed phases were synthesized by one-pot decomposition of (N-anil-N-piperldtc)Fe1 as FeS#1), (N-piperldtc)Fe2 as FeS#2) and (N-anildtc)Fe3 as FeS#3) complexes as precursors, with the help of tri-n-octylphosphine oxide (TOPO) coordinating solvent. Their morphology, stability, size, optical and structural characteristics were observed using various material characterization instruments. In comparison to the FeS#2 nano-flower shape, FeS#1 and FeS#3 have a uniform nano-rod shape. A one-step decomposition pattern was obtained from the thermal gravimetric analysis (TGA) results with 3% final mass residual. The high-resolution transmission electron microscopy (HRTEM) image reveals an aggregation and size diameter of around 14.47-30.25 nm for the three samples. The optical response between 3.8 and 4.2 eV from the three samples shows that they are inconsiderable materials for solar cells application. The diffraction peaks for the three samples matched well with the FeS/FeS2. These nanoscale materials can be used in a variety of applications, including lithium-ion batteries, biosensors, hydrogen evolution, and multifunctional nanocomposite materials.

Roles of TOPO Coordinating Solvent on Prepared Nano-Flower/Star and Nano-Rods Nickel Sulphides for Solar Cells Applications.

The present study describes a cheap, safe, and stable chemical process for the formation of nickel sulphide (NiS) with the use of mixed and single molecular precursors. The production pathway is uncomplicated, energy-efficient, quick, and toxic-free, with large-scale commercialization potential. The obtained results show the effect of tri-N-octylphosphine oxide (TOPO) as a coordinating solvent on the reaction chemistry, size distributions, morphology, and optical properties of both precursors. Ni[N,N-benz-N-p-anisldtc] as NiSa, Ni[N,N-benzldtc] as NiSb, and Ni[N-p-anisldtc] as NiSc thermally decompose in a single step at 333-334 °C. The X-ray diffraction peaks for NiSa, NiSb, and NiSc matched well with the cubic NiS nanoparticles and corresponded to planes of (111), (220), and (311). The extrapolated linear part from the Tauc plots reveals band gap values of 3.12 eV, 2.95 eV, and 2.5 eV, which confirms the three samples as potential materials for solar cell applications. The transmission electron microscopy (TEM) technique affirmed the quantum dot size distribution at 19.69-28.19 nm for NISa, 9.08-16.63 nm for NISb, and 9.37-10.49 nm for NISc, respectively. NiSa and NiSc show a clearly distinguishable flower/star like morphology, while NiSb displays a compact nano-rod shape. To the best of the authors' knowledge, very few studies have been reported on the flower/star like and nano-rod shapes, but none with the dithiocarbamate molecular precursor for NiS nanoparticles.

Proficient One-Step Heat-Up Synthesis of Manganese Sulfide Quantum Dots for Solar Cell Applications.

The necessity to develop renewable energy resources that are highly durable and flexible with superior energy density and capacitance ability has attracted considerable interest in the field of solar cell research. Semiconducting compound materials that are easily available, hazard-free and cost-effective are emerging as potential solutions to tackle this challenge. Herein, we present multiple molecular precursors used to grow manganese sulfide nanoparticles through a proficient one-step heat-up approach. For all of the tested samples, the X-ray diffraction peaks correspond to a γ-MnS hexagonal wurtzite structure. UV-Vis spectroscopy yielded absorption wavelengths of 359-420 nm and band-gap energies of 3.78-4.0 eV. Photoluminescence analysis shows characteristics of red and blue shift from 451-602 nm. High-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED) reveal a narrow size distribution with nanosticks and large contact areas, which are critical for improved catalytic performance. The current study provides an improved pathway to a well-grown and uniform nanocrystal structure for applications in energy devices.

Chalcogenide Perovskites and Perovskite-Based Chalcohalide as Photoabsorbers: A Study of Their Properties, and Potential Photovoltaic Applications.

In 2015, a class of unconventional semiconductors, Chalcogenide perovskites, remained projected as possible solar cell materials. The MAPbI3 hybrid lead iodide perovskite has been considered the best so far, and due to its toxicity, the search for potential alternatives was important. As a result, chalcogenide perovskites and perovskite-based chalcohalide have recently been considered options and potential thin-film light absorbers for photovoltaic applications. For the synthesis of novel hybrid perovskites, dimensionality tailoring and compositional substitution methods have been used widely. The study focuses on the optoelectronic properties of chalcogenide perovskites and perovskite-based chalcohalide as possibilities for future photovoltaic applications.

Modeling and experimental analysis of battery charge controllers for comparing three off-grid photovoltaic power plants.

The study of battery charge algorithm as a sole power storage agent in off-grid systems is essential. The battery charge algorithm has various methods, and the battery in these methods relies on the quantity of charges. Hence, a charge controller is used to safeguard and regulate battery charge and discharge for off-grid photovoltaic (PV) systems. This study presents the 11.4 kWp power plant analysis comprising three 3.8 kWp each of off-grid, hybrid and grid-assisted systems with battery capacities of 900 Ah, 1235 Ah and 910 Ah, respectively, where all the systems were reconfigured to function as off-grids. The battery charge controller charges the lead-acid battery using a three-stage charging strategy, including constant current, constant voltage and float charge stage. A DT80 data logger was installed to simultaneously record the electrical parameters of the systems, while Kipp & Zonen CMP 11 pyranometer was selected to measure solar radiation data. Experimentation with three electric bar heaters, each with fan and humidifier, were used as loads to draw constant power of 1.2 kW from batteries of each system on charging and discharging on an overcast and clear sky days for a week. The useful study is performed in the following ways, MPPT tracking performance, battery charging and discharging performance and charge controller efficiency. The performance results reveal that the MPPT can track the PV module maximum point at solar irradiance from 07h15 to around 12h00 maximum power tracking efficiency. An irradiance of illumination fluctuates from 5 W/m2 to 850 W/m2 while the electrical energy consumed by the loads in off-grid, hybrid and grid-assisted systems are 456.12, 568.87 and 80.00 Wh, respectively. It is estimated that individual owners could charge electric appliances from residential and commercial buildings of solar arrays of clean, renewable solar energy.

Inorganic Pb(II)-P and Pb(II)-S Complexes as Photosensitizers from Primary and Secondary Amines in Dyes-Sensitized Solar Cells.

Pb(II) complexes of bis(N-1,4-phenyl-N-(4-morpholinedithiocarbamato)) as Pb(II)-S and bis(N-diisopropyl-N-octyldithiocarbamato) as Pb(II)-P were prepared and characterized by optical, structural, morphological, and electrochemical techniques. The scanning electron microscopy analysis of Pb(II)-P and Pb(II)-S complexes consists of cubic crystals. X-ray diffraction and high-resolution transmission electron microscopy spectral studies revealed that the diameter increases in length for alkyl chain groups. This study demonstrates that the cubic shape of Pb(II) complexes can be synthesized from aromatic and aliphatic dithiocarbamate ligands. Photoluminescence analysis of both complexes fell within the blue shift region. The CV curve for Pb(II)-S revealed redox curves and the box-like shape as an indicative of a capacitive behavior, signifying limited catalytic redox activity. The J-V results for both sensitizers displayed satisfactory conversion efficiency (% η) between 3.77 and 3.96%.

Colloidal Synthesis and Characterization of Molybdenum Chalcogenide Quantum Dots Using a Two-Source Precursor Pathway for Photovoltaic Applications.

The drawbacks of utilizing nonrenewable energy have quickened innovative work on practical sustainable power sources (photovoltaics) because of their provision of a better-preserved decent environment which is free from natural contamination and commotion. Herein, the synthesis, characterization, and application of Mo chalcogenide nanoparticles (NP) as alternative sources in the absorber layer of QDSSCs is discussed. The successful synthesis of the NP was confirmed as the results from the diffractive peaks obtained from XRD which were positive and agreed in comparison with the standard. The diffractive peaks were shown in the planes (100), (002), (100), and (105) for the MoS2 nanoparticles; (002), (100), (103), and (110) for the MoSe2 nanoparticles; and (0002), (0004), (103), as well as (0006) for the MoTe2 nanoparticles. MoSe2 presented the smallest size of the nanoparticles, followed by MoTe2 and, lastly, by MoS2. These results agreed with the results obtained using SEM analysis. For the optical properties of the nanoparticles, UV-Vis and PL were used. The shift of the peaks from the red shift (600 nm) to the blue shift (270-275 nm and 287-289 nm (UV-Vis)) confirmed that the nanoparticles were quantum-confined. The application of the MoX2 NPs in QDSSCs was performed, with MoSe2 presenting the greatest PCE of 7.86%, followed by MoTe2 (6.93%) and, lastly, by MoS2, with the PCE of 6.05%.

A Review on Lead-Free Hybrid Halide Perovskites as Light Absorbers for Photovoltaic Applications Based on Their Structural, Optical, and Morphological Properties.

Despite the advancement made by the scientific community in the evolving photovoltaic technologies, including the achievement of a 29.1% power conversion efficiency of perovskite solar cells over the past two decades, there are still numerous challenges facing the advancement of lead-based halide perovskite absorbers for perovskite photovoltaic applications. Among the numerous challenges, the major concern is centered around the toxicity of the emerging lead-based halide perovskite absorbers, thereby leading to drawbacks for their pragmatic application and commercialization. Hence, the replacement of lead in the perovskite material with non-hazardous metal has become the central focus for the actualization of hybrid perovskite technology. This review focuses on lead-free hybrid halide perovskites as light absorbers with emphasis on how their chemical compositions influence optical properties, morphological properties, and to a certain extent, the stability of these perovskite materials.

Electrochemistry of Inorganic OCT-PbS/HDA and OCT-PbS Photosensitizers Thermalized from Bis(N-diisopropyl-N-octyldithiocarbamato) Pb(II) Molecular Precursors.

Inorganic nanocrystal solar cells have been tagged as the next generation of synthesizers that have the potential to break new ground in photovoltaic cells. This synthetic route offers a safe, easy and cost-effective method of achieving the desired material. The present work investigates the synthesis of inorganic PbS sensitizers through a molecular precursor route and their impact on improving the conversion efficiency in photovoltaic cells. PbS photosensitizers were deposited on TiO2 by direct deposition, and their structure, morphologies and electrocatalytic properties were examined. The X-ray diffraction (XRD) confirms PbS nanocrystal structure and the atomic force microscopy (AFM) displays the crystalline phase of uniform size and distribution of PbS, indicating compact surface nanoparticles. The electrocatalytic activity by lead sulfide, using N-di-isopropyl-N-octyldithiocarbamato (OCT) without hexadecylamine (HDA) capping (OCT-PbS) was very low in HI-30 electrolyte, due to its overpotential, while lead sulfide with OCT and HDA-capped (OCT-PbS/HDA) sensitizer exhibited significant electrocatalytic activity with moderate current peaks due to a considerable amount of reversibility. The OCT-PbS sensitizer exhibited a strong resistance interaction with the electrolyte, indicating very poor catalytic activity compared to the OCT-PbS/HDA sensitizer. The values of the open-circuit voltage (VOC) were ~0.52 V, with a fill factor of 0.33 for OCT-PbS/HDA. The better conversion efficiency displayed by OCT-PbS/HDA is due to its nanoporous nature which improves the device performance and stability.

Electrochemical Performance of Photovoltaic Cells using HDA Capped-SnS Nanocrystal from bis (N-1,4-Phenyl-N-Morpho-Dithiocarbamato) Sn(II) Complexes.

Great consideration is placed on the choice of capping agents' base on the proposed application, in order to cater to the particular surface, size, geometry, and functional group. Change in any of the above can influence the characteristics properties of the nanomaterials. The adoption of hexadecylamine (HDA) as a capping agent in single source precursor approach offers better quantum dots (QDs) sensitizer materials with good quantum efficiency photoluminescence and desirable particles size. Structural, morphological, and electrochemical instruments were used to evaluate the characterization and efficiency of the sensitizers. The cyclic voltammetry (CV) results display both reduction and oxidation peaks for both materials. XRD for SnS/HDA and SnS photosensitizers displays eleven peaks within the values of 27.02° to 66.05° for SnS/HDA and 26.03° to 66.04° for SnS in correlation to the orthorhombic structure. Current density-voltage (I-V) results for SnS/HDA exhibited a better performance compared to SnS sensitizers. Bode plot results indicate electrons lifetime (τ) for SnS/HDA photosensitizer have superiority to the SnS photosensitizer. The results connote that SnS/HDA exhibited a better performance compared to SnS sensitizers due to the presence of HDA capping agent.

The Frontiers of Nanomaterials (SnS, PbS and CuS) for Dye-Sensitized Solar Cell Applications: An Exciting New Infrared Material.

To date, extensive studies have been done on solar cells on how to harness the unpleasant climatic condition for the binary benefits of renewable energy sources and potential energy solutions. Photovoltaic (PV) is considered as, not only as the future of humanity's source of green energy, but also as a reliable solution to the energy crisis due to its sustainability, abundance, easy fabrication, cost-friendly and environmentally hazard-free nature. PV is grouped into first, second and third-generation cells. Dye-sensitized solar cells (DSSCs), classified as third-generation PV, have gained more ground in recent times. This is linked to their transparency, high efficiency, shape, being cost-friendly and flexibility of colour. However, further improvement of DSSCs by quantum dot sensitized solar cells (QDSSCs) has increased their efficiency through the use of semiconducting materials, such as quantum dots (QDs), as sensitizers. This has paved way for the fabrication of semiconducting QDs to replace the ideal DSSCs with quantum dot sensitized solar cells (QDSSCs). Moreover, there are no absolute photosensitizers that can cover all the infrared spectrum, the infusion of QD metal sulphides with better absorption could serve as a breakthrough. Metal sulphides, such as PbS, SnS and CuS QDs could be used as photosensitizers due to their strong near infrared (NIR) absorption properties. A few great dependable and reproducible routes to synthesize better QD size have attained much ground in the past and of late. The injection of these QD materials, which display (NIR) absorption with localized surface plasmon resonances (SPR), due to self-doped p-type carriers and photocatalytic activity could enhance the performance of the solar cell. This review will be focused on QDs in solar cell applications, the recent advances in the synthesis method, their stability, and long term prospects of QDSSCs efficiency.

Structural, Morphological and Electrochemical Characterization of Hydrothermally Fabricated PdNiCo and PdNiCo-rGO Alloys for Use as Counter Electrode Catalysts in DSSC.

The hydrothermal fabrication and characterization of ternary palladium alloys PdNiCo and PdNiCo-rGO, which could be potential replacements to the expensive and corrosion susceptible platinum counter electrode in dye sensitized solar cells is hereby reported in this article. The synergy created by combining three metallic elements as well as the effect of carbon supports was investigated. The as-synthesized alloys consisted of agglomerated spherical particles. Comparison of the electrochemical analysis data showed that PdNiCo-rGO counter electrode could be a potential replacement for the platinum counter electrode with reduction current density, peak to peak potential difference, charge transfer resistance and power conversion efficiency of 21 mA∙cm-2, 0.12 mV, 0.726 Ω and 4.36% respectively.

Synthesis, Characterization and Optimization of Hydrothermally Fabricated Binary Palladium Alloys PdNix for Use as Counter Electrode Catalysts in Dye Sensitized Solar Cells.

The hydrothermal synthesis, characterization and optimization of binary palladium alloys PdNix is hereby presented in this work. Comparison of the reduction capability of the developed PdNix alloys intended for use as alternative counter electrode catalysts in dye sensitized solar cells was made relative to the standard platinum counter electrode catalyst as well as the carbon supported PdNi-rGO sample. Optimization was accomplished through varying the molar ratio of the reagents. The unsupported PdNi3 sample produced the highest catalytic efficiency with reduction current density, peak to peak potential difference and charge transfer resistance of 35 mA cm-2, 0.15 mV and 0.47 Ω respectively. Obtained results show that the unsupported PdNi3 alloy was catalytically more effective than the platinum and PdNi-rGO thus could be a viable replacement in dye sensitized solar cell counter electrodes.

Metal Sulphides and Their Carbon Supported Composites as Platinum-Free Counter Electrodes in Dye-Sensitized Solar Cells: A Review.

Energy sufficiency is a critical requirement for the economic prosperity of modern countries. Efficient harnessing of solar energy using technologies such as the dye-sensitized solar cell could solve the energy problem which persistently plagues developing countries. Despite having a simple operational procedure and modest power conversion efficiency of 13.8%, the dye-sensitized solar cell consists of an expensive platinum counter electrode which makes commercial success futile. Thus, this review intends to establish the progress researchers have attained in the development of sulphide based counter electrodes as alternatives to platinum, thereby lowering cost of production. Metallic sulphides are good electrocatalysts and cheap, hence, they possess the necessary requirements for effective functional counter electrodes. Furthermore, ternary metallic sulphides are known to exhibit higher efficiencies stemming from the synergistic effect produced by the co-existence of two metal ions in a crystal structure, which is believed to induce greater catalytic capability. Incorporation of metallic sulphides with carbon materials, which are exceptional electrical conductors, could potentially produce more efficient counter electrodes. In that regard, this review seeks to establish the effect recently developed composite counter electrodes comprising metallic sulphides and carbon-based materials have induced on the functionality of the counter electrode (CE).

Antibiotic Use in Agriculture and Its Consequential Resistance in Environmental Sources: Potential Public Health Implications.

Due to the increased demand of animal protein in developing countries, intensive farming is instigated, which results in antibiotic residues in animal-derived products, and eventually, antibiotic resistance. Antibiotic resistance is of great public health concern because the antibiotic-resistant bacteria associated with the animals may be pathogenic to humans, easily transmitted to humans via food chains, and widely disseminated in the environment via animal wastes. These may cause complicated, untreatable, and prolonged infections in humans, leading to higher healthcare cost and sometimes death. In the said countries, antibiotic resistance is so complex and difficult, due to irrational use of antibiotics both in the clinical and agriculture settings, low socioeconomic status, poor sanitation and hygienic status, as well as that zoonotic bacterial pathogens are not regularly cultured, and their resistance to commonly used antibiotics are scarcely investigated (poor surveillance systems). The challenges that follow are of local, national, regional, and international dimensions, as there are no geographic boundaries to impede the spread of antibiotic resistance. In addition, the information assembled in this study through a thorough review of published findings, emphasized the presence of antibiotics in animal-derived products and the phenomenon of multidrug resistance in environmental samples. This therefore calls for strengthening of regulations that direct antibiotic manufacture, distribution, dispensing, and prescription, hence fostering antibiotic stewardship. Joint collaboration across the world with international bodies is needed to assist the developing countries to implement good surveillance of antibiotic use and antibiotic resistance.

An Overview of the Control of Bacterial Pathogens in Cattle Manure.

Cattle manure harbors microbial constituents that make it a potential source of pollution in the environment and infections in humans. Knowledge of, and microbial assessment of, manure is crucial in a bid to prevent public health and environmental hazards through the development of better management practices and policies that should govern manure handling. Physical, chemical and biological methods to reduce pathogen population in manure do exist, but are faced with challenges such as cost, odor pollution, green house gas emission, etc. Consequently, anaerobic digestion of animal manure is currently one of the most widely used treatment method that can help to salvage the above-mentioned adverse effects and in addition, produces biogas that can serve as an alternative/complementary source of energy. However, this method has to be monitored closely as it could be fraught with challenges during operation, caused by the inherent characteristics of the manure. In addition, to further reduce bacterial pathogens to a significant level, anaerobic digestion can be combined with other methods such as thermal, aerobic and physical methods. In this paper, we review the bacterial composition of cattle manure as well as methods engaged in the control of pathogenic microbes present in manure and recommendations that need to be respected and implemented in order to prevent microbial contamination of the environment, animals and humans.

Inactivation of selected bacterial pathogens in dairy cattle manure by mesophilic anaerobic digestion (balloon type digester).

Anaerobic digestion of animal manure in biogas digesters has shown promise as a technology in reducing the microbial load to safe and recommended levels. We sought to treat dairy manure obtained from the Fort Hare Dairy Farm by investigating the survival rates of bacterial pathogens, through a total viable plate count method, before, during and after mesophilic anaerobic digestion. Different microbiological media were inoculated with different serial dilutions of manure samples that were withdrawn from the biogas digester at 3, 7 and 14 day intervals to determine the viable cells. Data obtained indicated that the pathogens of public health importance were 90%-99% reduced in the order: Campylobacter sp. (18 days) < Escherichia coli sp. (62 days) < Salmonella sp. (133 days) from a viable count of 10.1 × 103, 3.6 × 105, 7.4 × 103 to concentrations below the detection limit (DL = 102 cfu/g manure), respectively. This disparity in survival rates may be influenced by the inherent characteristics of these bacteria, available nutrients as well as the stages of the anaerobic digestion process. In addition, the highest p-value i.e., 0.957 for E. coli showed the statistical significance of its model and the strongest correlation between its reductions with days of digestion. In conclusion, the results demonstrated that the specific bacterial pathogens in manure can be considerably reduced through anaerobic digestion after 133 days.

Microbial anaerobic digestion (bio-digesters) as an approach to the decontamination of animal wastes in pollution control and the generation of renewable energy.

With an ever increasing population rate; a vast array of biomass wastes rich in organic and inorganic nutrients as well as pathogenic microorganisms will result from the diversified human, industrial and agricultural activities. Anaerobic digestion is applauded as one of the best ways to properly handle and manage these wastes. Animal wastes have been recognized as suitable substrates for anaerobic digestion process, a natural biological process in which complex organic materials are broken down into simpler molecules in the absence of oxygen by the concerted activities of four sets of metabolically linked microorganisms. This process occurs in an airtight chamber (biodigester) via four stages represented by hydrolytic, acidogenic, acetogenic and methanogenic microorganisms. The microbial population and structure can be identified by the combined use of culture-based, microscopic and molecular techniques. Overall, the process is affected by bio-digester design, operational factors and manure characteristics. The purpose of anaerobic digestion is the production of a renewable energy source (biogas) and an odor free nutrient-rich fertilizer. Conversely, if animal wastes are accidentally found in the environment, it can cause a drastic chain of environmental and public health complications.