Porous silicon films are heavily used in technology. Their optical and electrical characteristics should be manipulated based on their application. Such characteristics can be tailored by controlling ...their morphology and porosity. Various types of monocrystalline Si substrates, with (110) face and 500–550 μm thickness, with different doping concentrations and resistivity values, have been used here to prepare porous silicon films with various characteristics. Preparation conditions, such as etching time, current density, light exposure, and HF concentration in ethanol, have also been varied. Macro-, meso-, and nanoporous films were selectively prepared by controlling the preparation conditions. Measured optical and electrical characteristics for the film are affected by its morphology and porosity. The film morphology and porosity can in turn be varied depending on preparation conditions, despite the substrate resistivity and doping concentration. Among various prepared films, the nanoporous film exhibits best characteristics in terms of high uniformity, low reflectance, and low sheet resistance (28.76 Ω/sq), despite its high substrate resistivity. Porous silicon characteristics can thus be tailored as desired for optoelectronic applications, simply by controlling preparation conditions.
Natural waters are prone to pollution with organic contaminants, waste pharmaceuticals being an example. Pharmaceutical compounds are widely detected in different surface waters, such as lakes and ...rivers. Removal of such contaminants from water is therefore imperative. Different strategies are commonly followed such as adsorption, chlorination, ozonation, peroxidation and others. Each method has its shortcomings. Photodegradation of water organic contaminants by semiconductors is a safe and non-costly method. In photodegradation, the organic contaminant is completely mineralized with radiation and oxygen using stable semiconductor nanoparticles as photocatalysts. ZnO nanopowder is widely described for photodegradation processes. Due to its wide band gap (~3.2 eV) ZnO excitation is limited to UV radiation. Moreover, the nano-particle nature for the ZnO catalyst makes it difficult to recover and re-use after process completion. Supporting the ZnO nanoparticles onto stable solid material surfaces is one possible way out, and is studied here. Raw clay (kaolin) is described to support ZnO particles in photodegradation of a widely encountered pharmaceutical contaminant, tetracycline (TC). The results show the possibility of annealed ZnO/Kaolin to remove TC from water, firstly by adsorbing the contaminant then by photodegrading it into mineral species. The study shows that TC molecules pre-adsorbed onto ZnO/Kaolin were mineralized during photodegradation experiments. Complete mineralization of reacted contaminant molecules was confirmed by spectrophotometry, high performance liquid chromatography (HPLC) and total organic carbon (TOC) study. Control experiments with a cut-off filter (400 nm and shorter) confirmed the ability of the catalyst to function in the visible region, where contaminant molecules behave as sensitizers in the photodegradation process. Optimizing the efficiency of the ZnO catalyst in TC photodegradation processes by studying the effect of pH using the point of zero charge (pHPZC) concepts is achieved. Collectively, the results show the possibility to prepare an efficient recoverable ZnO/Kaolin catalyst, which can be sensitized with TC molecules themselves with optimal working pH range 6–9.
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•Nano-size ZnO particles are supported onto raw clay particles.•Supported ZnO/Clay effectively catalyses aqueous tetracycline mineralization.•Tetracycline molecules self-sensitize ZnO/Clay catalyst in the visible light.•Photo-degraded tetracycline molecules are completely mineralized.•ZnO/Clay particles retain photo-catalytic efficiency on multi-recovery and reuse.
•The intrinsic properties of MAPbX3 (X = I, Br and Cl) are described.•The optimized orthorhombic structures based on the ab-initio DFT calculation.•The obtained results are analyzed and compared to ...other data studies.
Organometallic halide perovskites (OMHPs) are absorbent materials, and can thus be employed in solar cells with power conversion efficiency (PEC) of 22% or higher. Using calculations, this work confirms earlier experimental findings and determines optimal properties to achieve maximum conversion efficiency for OMHPs. Values of energy band gap, density of states, absorption coefficient, refractive index, dielectric constant and elastic constants of orthorhombic methylamunium lead halides (MAPbX3) (X = I, Br and Cl) family are all calculated using Density Functional Theory (DFT) method with generalized gradient approximation (GGA). The stiffness of (MAPbX3) (X = I, Br and Cl) is investigated by calculating Young’s moduli E constants. Among the series, MAPbI3 is the stiffest material with Ex = 57.24 GPa. The perovskite family members are characterized by their energy band gap variation as: Eg MAPbI3, MAPbBr3, MAPbCl3 = 1.626, 2.207 and 2.748 eV, respectively. They also exhibit a remarkable absorption coefficient (α MAPbX3 = 105 cm−1) over a wide energy range particularly the visible spectrum 1.65–3.26 eV: 380–750 nm. The anisotropy of optical properties (MAPbX3) (X = I, Br) is proven in the near and middle ultraviolet 3.1–5 eV energy band.
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•p-NiO attracts special attention as a working electrode in p-DSSCs.•Spacers in dyes inhibit various recombination types and improve performance in p-DSSCs.•p-DSSC performance ...improves with dye HOMO level lower than NiO Valence Band.•Dye LUMO should be higher than Redox couple potential for higher p-DSSC performance.•Aluminum-doped zinc oxide is recommended in p-DSSCs.
Dye-sensitized-solar cells, DSSCs, are emerging as alternatives to traditional photovoltaic solar cells. Among them, p-type DSSCs attracted special attention due to their easy manufacturing methods, understandable operating mechanisms and friendliness to environment. In these solar cells, the fate of the excited electron is determined based on the kinetic competition that occurs between two processes: electron-hole charge separation and recombination processes. Additionally, the type of the electrolyte is responsible for another competition, namely between recombination reactions and the dye regeneration by the electrolyte. Early studies showed that p-DSSCs and n-DSSCs may be combined to create tandem solar cells (t-DSSCs). Nonetheless, the performance is normally very poor due to the above-mentioned competing processes, which dictates the need to improve DSSCs. Various semiconductor materials were described in manufacturing the working electrodes in DSSCs, among which NiO is the most common material. Therefore, special attention is paid to NiO as a working electrode (WE) here. Effects of sensitizer, redox couple and the transparent conducting oxide electrode with NiO electrode on the cell performance are discussed here with useful recommendations. Inserting spacers in the dye molecular structure can improve cell performance by improving dye regeneration and inhibiting charge recombination, as widely described. However, the effect of spatial separation within the dye has not been specifically reviewed earlier, and this review article is mainly devoted to such effect within the frameworks of spatial separation strategy. Sensitizer molecule aggregations are also discussed, with techniques to optimize dye loading without aggregation.
Heterojunctions based on
p
-CuO/
n
-ZnO, prepared by simple methods such as spin coating, normally exhibit low photoconversion efficiency and require modification. Doping the ZnO layer with ions such ...as Sn
4+
could be a solution. In this work, heterojunctions were prepared by two simple methods. In method 1, to prepare the CuO@ZnO junction, the
n
-ZnO layer was spin-coated on tin-doped indium oxide/glass substrates (ITO/glass) followed by spin coating of the
p
-CuO layer. In method 2, to prepare the ZnO@CuO/Cu sheet junction, the
p
-CuO layer was prepared by thermal oxidation of the Cu metal sheet, followed by spin coating of ZnO. In both cases, the ZnO film was doped with Sn
4+
ions at 1.5% concentration by mole. The effects of Sn-doping on the structural and morphological properties of the junction were comparatively studied by X-ray diffraction and atomic force microscopy. In both preparations, doping affected the optical, electrical and photovoltaic (PV) properties. The preparation method also affected junction characteristics, as preparation method 2 showed heterojunctions with higher PV characteristics. The results show inroads to improving PV characteristics for the heterojunction based on the proper preparation method and Sn doping.
Graphical Abstract
Carbon nanodots (CNDs) have many fascinating properties, such as optical properties (UV-Visible absorption and fluorescence emission), which make them good candidates in many applications, such as ...photocatalysts for the degradation of several organic pollutants. This study aims to synthesize CNDs from olive solid wastes at different carbonization temperatures from 300 to 900 °C and study the effect on the optical properties of the CNDs, such UV-Vis, fluorescence, quantum yield, and energy bandgap, in addition to the influence on the photoactivity of the CNDs as photocatalysts for the degradation of methylene blue (MB). CNDs were prepared from olive solid wastes (OSWs) by pyrolysis at different temperatures (300-900 °C) for conversion to carbonized material, and then oxidized chemically in the presence of hydrogen peroxide (H
2
O
2
). It was found that an increase in the carbonization temperature of the OSWs leads to an increase in the product yield with a maximum value at 500 °C, and it then decreased dramatically. On the other hand, a decrease in fluorescence due to the diminishment of oxygen groups and the destruction of the surface of the CNDs was observed. The higher quantum yield (5.17%) and bandgap (2.77 eV) were achieved for CNDs prepared from OSWs that carbonized at 300 °C. The rate and degradation efficiency of MB were studied with the different synthesized CNDs, and it was found that an increase in the carbonization temperature leads to a decrease in the rate and degradation efficiency of MB, with the highest degradation rate of 0.0575 min
−1
and degradation efficiency of 100% after 120 minutes of light irradiation being realized for the sample carbonized at 300 °C.
Carbon nanodots with different optical properties and photoactivity degrees as photocatalysts for the degradation of methylene blue are successfully synthesized from olive solid wastes at different carbonization temperatures.
•CIGS layer is made thinner to lower the cost, while a second CuZnSnSe (CZTSe)-layer absorber is added to maintain high cell performance.•The new proposed cell structure designed onto a ZnO-Al film ...that is experimentally electrodeposited onto FTO/Glass substrate, and then characterized.•The simulation has been conducted by the TCAD SILVACO using ATLAS module.•Alternatively, 22.40 to 29.22% efficiency improvement is achievable by CZTSe addition to a thin CIGS layer.
CuInGaSe (CIGS) based solar cells are promising, but involve costly and hazardous and costly indium element. This work aims at solving these problems, without sacrificing the benefits of CIGS systems. The approach is to use thinner CIGS layers. However, very thin layers minimize absorption and lower cell performance. Adding a second CuZnSnSe (CZTSe)-layer absorber should maintain high cell performance. The new proposed cell that has been simulated is MgF2/ZnO/Al/ZnO:i/CdS(n)/CZTSe(p)/CIGS(p)/Mo, with MgF2 antireflection layer, ZnO:i passivating layer, CdS emitter layer, CZTSe/CIGS double absorber layer, ZnO-Al transparent conductor oxide(TCO) and element almolybdenum (Mo) back contact. A ZnO-Al film has been experimentally electrodeposited onto FTO/Glass substrate, and then characterized. TCAD SILVACO using ATLAS module has been used in the simulation. Various parameters, including layer-thickness and doping-concentration, are optimized, keeping smaller CIGS-layer thickness. Band-diagrams, carrier-concentrations and current–density, in addition to possible recombination processes, are investigated to assess performance enhancement. The results show that increasing the one-absorber CIGS-layer thickness by 2.5-fold, increases conversion efficiency from 22.3 to 24.3% only, which does not justify the extra costs. Alternatively, efficiency improves from 22.40 to 29.22% by adding CZTSe to a thin 1.0 μm CIGS layer. In conclusion, the study highlights the added value for the second-absorber layer.
Correction for 'Optical properties and photoactivity of carbon nanodots synthesized from olive solid wastes at different carbonization temperatures' by Shadi Sawalha
et al.
,
RSC Adv.
, 2022,
12
, ...4490-4500,
https://doi.org/10.1039/D1RA09273A
.
Heterojunction silicon solar cells, also known as heterojunctions with intrinsic thin layer (HIT) of the type TCO/n-a-Si:H/i-a-Si:H/p–c-Si/p
+
-a-Si:H/BSF solar cells (where TCO is transparent ...conducting oxide involving Al-doped ZnO; a-Si:H is hydrogenated amorphous silicon; c-Si:H is hydrogenated crystalline silicon; BSF is back surface field, n- and p- refer to
n
-type and
p
-type, respectively; n-a-Si is the emitter layer; i-a-Si is the passivation layer of intrinsic type semiconductor) have attracted special interest due to their suitability and high efficiency. Thickness and work function for the TCO layer, together with thickness and doping density of the emitter layer, are all optimized here. With optimal parameters, TCO/n-a-Si:H/i-a-Si:H/p-c-Si/p
+
-a-Si:H/BSF solar cells exhibit high simulation characteristics in terms of conversion efficiency (25.62%), open circuit potential (
V
OC
, 744 mV), short circuit current density (
J
SC
, 42.43 mA/cm
2
) and fill factor (FF, 83.7%). The
Automat for Simulation of Heterostructures
(
AFORS
-
HET
) program is used. The energy band diagram, current density, quantum efficiency, and charge-carrier generation/recombination behaviours are investigated to find out how hetero-junction cell performance enhancement occurs.
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•Aqueous Enterococcus (Gram +) &Proteus mirabilis (Gram −) bacteria are photodegrded.•ZnO nanoparticles partly inactivate both aqueous bacteria in the dark.•With solar simulated light ...ZnO catalyzes complete inactivation of bacteria in 30 min.•Bacterial mineralization is photocatalyzed by ZnO in 4 h leaving no organics.
ZnO nanoparticles have been effectively used in water disinfection from two common types of gram-positive (Enterococcus faecium) and gram–negative (Proteus mirabilis) bacteria under simulated solar radiations by inactivation. Complete mineralization of organic contents that leach out of inactivated bacteria has also been achieved leaving no soluble organic matter in water. Bacterial inactivation and complete mineralization have been confirmed by plate counting, high performance liquid chromatography and total organic content measurement. Effects of different reaction parameters (pH, temperature, bacterial concentration, reaction time and ZnO catalyst loading) have all been studied. Control experiments with Cut-off filters confirm the role of the UV tail in solar simulated light in the photocatalytic process. The results highlight the feasibility of using ZnO photocatalyst in complete disinfection of water from both hazardous Enterococcus and Proteus mirabilis bacteria, leaving no organic matters after degradation.
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