Numerical assessment of optoelectrical properties of ZnSe-CdSe solar cell-based with ZnO antireflection coating layer

In this work, a numerical assessment of the optoelectrical properties of the ZnO-ZnSe-CdSe heterojunction for a thin and cost-effective solar cell was made by using the PC1D simulation software. The photovoltaic (PV) properties have been optimized by varying thicknesses of the absorber layer of the p-CdSe layer, the window layer of n-ZnSe, and the antireflection coating (ARC) layer of ZnO, a transparent conductive oxide with enhanced light trapping, and wide bandgap engineering. There is a positive conduction band offset (CBO) of ΔEc = 0.25 eV and a negative valence band offset (VBO) of ΔEv = 1.2 - 2.16 =  - 0.96 eV. The positive CBO prevents the flow of electrons from the CdSe to the ZnSe layer. Further, the impact of doping concentration on the performance of solar cells has been analyzed. The simulation results reveal the increase in the efficiency of solar cells by adding an ARC. The rapid and sharp increase in the efficiency with the thickness of the window layer beyond 80 nm is interesting, unusual, and unconventional due to the combined effect of morphology and electronics on a macro-to-micro scale. The thin-film solar cell with the structure of ZnO/ZnSe/CdSe exhibited a high efficiency of 11.98% with short-circuit current (I_sc) = 1.72 A, open-circuit voltage (V_oc) = 0.81 V and fill factor (FF) = 90.8% at an optimized thickness of 2 μm absorber layer, 50 nm window layer, and 78 nm ARC layer. The EQE of solar cells has been observed at about 90% at a particular wavelength at 470 nm (visible light range). Around 12% of efficiency from such a thin-layered solar cell is highly applicable.

Silica sand-supported nano zinc oxide-graphene oxide composite induced rapid photocatalytic decolorization of azo dyes under sunlight and improved antimicrobial activity

Here, silica sand-supported heterojunction composite of nano zinc oxide (nZnO) and graphene oxide nanosheet (nZnO-GO@SS) was prepared, and its potential as an efficient photocatalyst for the degradation of methylene blue (MB) and Rhodamine-B (Rh-B) under sunlight was demonstrated. Transmission electron microscopy confirmed the uniform distribution of spherically shaped nZnO of average size of approximately 8 nm over graphene oxide nanosheet (GO) in the composites. Photodegradation yields of 95.3% and 97.5% for 100 ppm of MB and Rh-B dye within 150 and 220 min, respectively, were achieved under sunlight by the prepared nanocatalyst (nZnO-GO), while sand microparticle-supported nanocatalyst (nZnO-GO@SS) demonstrated faster degradation of MB and Rh-B, i.e., within 120 and 160 min, respectively. Furthermore, when the recyclability of the photocatalyst was studied, the nZnO-GO exhibited more than 80% degradation efficiency after five cycles for both the dyes and nZnO-GO@SS demonstrated 10% higher (~90%) removal capability after five cycles of reuse. Furthermore, the antibacterial assay showed complete inactivation of Escherichia coli and Staphylococcus aureus bacterial strain by nZnO-GO@SS. Hence, our proposed strategy for the removal of toxic dyes from the aquatic environment under sunlight proved that sand microparticle-supported nanocatalyst (nZnO-GO@SS) might be a superior, cost-effective, and suitable photocatalytic system for industrial applications toward toxic dye removal and decontamination from industrial wastewater.

Fabrication and characterization of ZnO/Se1-xTex solar cells

Selenium (Se) element is a promising light-harvesting material for solar cells because of the large absorption coefficient and prominent photoconductivity. However, the efficiency of Se solar cells has been stagnated for a long time owing to the suboptimal bandgap (> 1.8 eV) and the lack of a proper electron transport layer. In this work, we tune the bandgap of the absorber to the optimal value of Shockley-Queisser limit (1.36 eV) by alloying 30% Te with 70% Se. Simultaneously, ZnO electron transport layer is selected because of the proper band alignment, and the mild reaction at ZnO/Se_0.7Te_0.3 interface guarantees a good-quality heterojunction. Finally, a superior efficiency of 1.85% is achieved on ZnO/Se_0.7Te_0.3 solar cells.

Structural, Optical, and Photocatalytic Properties of ZnSe Nanoparticles Influenced by the Milling Time

ZnSe nanoparticles (NPs) were prepared by combining both hydrothermal and mechanical milling methods. Transmission electron microscopy images show that fabricated ZnSe NPs with a sphere-like shape have an average size (d) in the range of 20–100 nm, affected by changing the milling time from 10 to 60 min. All the samples crystalize in zincblende-type structure without impurities, as confirmed by analyzing X-ray diffraction patterns, Raman spectra, and energy-dispersive X-ray spectroscopy. Carefully checking Raman spectra, we have observed the broadening and redshift of vibration modes as decreasing NP size, which are ascribed to extra appearance of disorder and defects. The photoluminescence study has found a blue emission at 462 nm attributed to the excitonic near-band edge and a broad defect-related emission around 520–555 nm. Increasing milling time leads to the decrease in the exciton-emission intensity, while the defect-related emissions increase gradually. Interestingly, as decreasing d, we have observed an improved photodegradation of Rhodamine B under UV irradiation, proving application potentials of ZnSe NPs in photocatalytic activity.

Morphological, Material, and Optical Properties of ZnO/ZnS/CNTs Nanocomposites on SiO2 Substrate

Ultraviolet A light (UV-A, 320-400 nm), which is unblockable by sunscreen, requires careful detection for disease avoidance. In this study, we propose a novel photosensing device capable of detecting UV-A. Cancer-causing UV light can be simultaneously monitored with tiny rapid response sensors for a high carrier transition speed. In our research, a multifunctional ZnO/ZnS nanomaterial hybrid-sprinkled carbon nanotube (CNT) was created for the purpose of fabricating a multipurpose, semiconductorbased application. For our research, ZnO nanorods (NRs) were grown by using a facile hydrothermal method on SiO2 substrate, then vulcanized to form ZnO/ZnS coreshell nanorods, which were sprinkled with carbon nanotubes (CNTs). Results indicate that SiO2/ZnO/ZnS/CNT structures exhibited a stronger conducting current with and without light than those samples without CNTs. Multiple material characterizations of the nanostructures, including of atomic force microscopy (AFM) surface morphology evaluation, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) indicate that CNTs could be successfully spread on top of the ZnO/ZnS coreshell structures. Furthermore, chemical binding properties, material crystallinity, and optical properties were examined by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and photoluminescence (PL). Owing to their compact size, simple fabrication, and low cost, ZnO/ZnS coreshell NRs/CNT/SiO2-based nanocomposites are promising for future industrial optoelectronic applications.

Twin-ZnSe nanowires as surface enhanced Raman scattering substrate with significant enhancement factor upon defect

Semiconductor-based surface enhanced Raman scattering (SERS) substrate design has attracted much interest due to the excellent photoelectronic and biochemical properties. The structural change caused by twin in semiconductor will have an influence on improving the Raman signals enhancement based on the chemical mechanism (CM). Here, we demonstrated the twin in semiconductor ZnSe nanowires as an ultrasensitive CM-based SERS platform. The SERS signals of the rhodamine 6G (R6G) and crystal violet (CV) molecules adsorbed on twin-ZnSe nanowires could be easily detected even with an ultralow concentration of 10^-11 M and 10^-8 M, respectively, and the corresponding enhancement factor (EF) were up to 6.12 × 10⁷ and 3.02 × 10⁵, respectively. In addition, the charge transfer (CT) between the twin-ZnSe nanowires and R6G molecule has been demonstrated theoretically with first-principles calculations based on density-functional theory (DFT). These results demonstrated the proposed ZnSe nanowires with twin as SERS substrate has a broader application in the field of biochemical sensing.

Two Hybrid Au-ZnO Heterostructures with Different Hierarchical Structures: Towards Highly Efficient Photocatalysts

A new paradigm for photocatalysts based on two different hierarchically structured honeycomb and porous cylindrical Au-ZnO heterostructures was successfully developed via a straightforward and cost-effective hydrothermal method under different preparation conditions, which can be promising for industrial applications. The photocatalytic performance of all as-prepared samples under the illumination of sunlight was evaluated by the photocatalytic degradation of rhodamine B (RhB) and malachite green (MG) aqueous solutions. The results show that the photocatalytic degradation efficiency of RhB and MG was 55.3% and 40.7% for ZnO, 95.3% and 93.4% for the porous cylindrical Au-ZnO heterostructure, and 98.6% and 99.5% for the honeycomb Au-ZnO heterostructure, respectively. Compared with those from the ZnO, the results herein demonstrate an excellent reduction in the photoluminescence and improvement in the photocatalysis for the Au-ZnO hybrids with different morphologies. These results were attributed not only to the greatly improved sunlight utilization efficiency due to the surface plasmon resonance (SPR) absorption of Au nanoparticles in the visible region coupled with the UV light utilization by the ZnO nanostructures and multi-reflections of the incident light in the pore structures of their interior cavities but also to the high charge separation efficiency and low Schottky barrier generated by the combination of Au nanoparticles and ZnO micromaterials. Moreover, the honeycomb Au-ZnO heterostructure had a high Au content, surface area and surface oxygen vacancy (O_V), which enabled photocatalytic properties that were higher than those of the porous cylindrical Au-ZnO heterostructures. In addition, two different formation mechanisms for the morphology and possible photocatalytic mechanisms are proposed in this paper.

Flexible Photocatalytic Paper with Cu2O and Ag Nanoparticle-Decorated ZnO Nanorods for Visible Light Photodegradation of Organic Dye

We report on the fabrication of flexible photocatalytic paper comprised of Cu₂O and Ag nanoparticle (NP)-decorated ZnO nanorods (NRs) and its application in visible light photodegradation of organic dye. ZnO NRs are first grown on a kraft paper substrate using a hydrothermal method. The NRs are subsequently decorated with Cu₂O, Ag, or both NPs formed by photoreduction processes. Scanning electron microscopy and X-ray diffraction analysis confirm the crystallinity of ZnO NRs. Transmission electron microscopy analysis confirms the compositions of the two types of NPs. Four different types of photocatalytic papers with a size of 10 × 10 cm² are prepared and used to degrade a 10-μM and 100-mL rhodamine B solution. The paper with Cu₂O and Ag NP-co-decorated ZnO NRs has the best efficiency with first-order kinetic constants of 0.017 and 0.041 min^-1 under the illumination of a halogen lamp and direct sunlight, respectively. The performance of the photocatalytic paper compares well with other substrate-supported ZnO nanocomposite photocatalysts. With the advantages of flexibility, light weight, nontoxicity, low cost, and ease of fabrication, the photocatalytic paper has good potential for visible light photocatalysis.

ZnSe Nanorods as Visible-Light Absorbers for Photocatalytic and Photoelectrochemical H2 Evolution in Water

A precious-metal- and Cd-free photocatalyst system for efficient H₂ evolution from aqueous protons with a performance comparable to Cd-based quantum dots is presented. Rod-shaped ZnSe nanocrystals (nanorods, NRs) with a Ni(BF₄ )₂ co-catalyst suspended in aqueous ascorbic acid evolve H₂ with an activity up to 54±2 mmol H 2  g_ZnSe ^-1  h^-1 and a quantum yield of 50±4 % (λ=400 nm) under visible light illumination (AM 1.5G, 100 mW cm^-2 , λ>400 nm). Under simulated full-spectrum solar irradiation (AM 1.5G, 100 mW cm^-2 ), up to 149±22 mmol H 2  g_ZnSe ^-1  h^-1 is generated. Significant photocorrosion was not noticeable within 40 h and activity was even observed without an added co-catalyst. The ZnSe NRs can also be used to construct an inexpensive delafossite CuCrO₂ photocathode, which does not rely on a sacrificial electron donor. Immobilized ZnSe NRs on CuCrO₂ generate photocurrents of around -10 μA cm^-2 in an aqueous electrolyte solution (pH 5.5) with a photocurrent onset potential of approximately +0.75 V vs. RHE. This work establishes ZnSe as a state-of-the-art light absorber for photocatalytic and photoelectrochemical H₂ generation.

Engineering Charge Transfer Characteristics in Hierarchical Cu₂S QDs @ ZnO Nanoneedles with p⁻n Heterojunctions: Towards Highly Efficient and Recyclable Photocatalysts

Equipped with staggered gap p-n heterojunctions, a new paradigm of photocatalysts based on hierarchically structured nano-match-shaped heterojunctions (NMSHs) Cu₂S quantum dots (QDs)@ZnO nanoneedles (NNs) are successfully developed via engineering the successive ionic layer adsorption and reaction (SILAR). Under UV and visible light illumination, the photocatalytic characteristics of Cu₂S@ZnO heterojunctions with different loading amounts of Cu₂S QDs are evaluated by the corresponding photocatalytic degradation of rhodamine B (RhB) aqueous solution. The results elaborate that the optimized samples (S3 serial specimens with six cycles of SILAR reaction) by means of tailored the band diagram exhibit appreciable improvement of photocatalytic activities among all synthesized samples, attributing to the sensitization of a proper amount of Cu₂S QDs. Such developed architecture not only could form p⁻n junctions with ZnO nanoneedles to facilitate the separation of photo-generated carries but also interact with the surface defects of ZnO NNs to reduce the electron and hole recombination probability. Moreover, the existence of Cu₂S QDs could also extend the light absorption to improve the utilization rate of sunlight. Importantly, under UV light S3 samples demonstrate the remarkably enhanced RhB degradation efficiency, which is clearly testified upon the charge transfer mechanism discussions and evaluations in the present work. Further supplementary investigations illustrate that the developed nanoscale Cu₂S@ZnO heterostructures also possess an excellent photo-stability during our extensive recycling photocatalytic experiments, promising for a wide range of highly efficient and sustainably recyclable photocatalysts applications.

One-dimensional Ag3PO4/TiO2 heterostructure with enhanced photocatalytic activity for the degradation of 4-nitrophenol

A one-dimensional Ag₃PO₄/TiO₂ heterostructure exhibits enhanced photocatalytic activity due to the good visible light absorption capability and excellent charge separation characteristics of the formed heterojunction.

SnS2 nanosheet-based microstructures with high adsorption capabilities and visible light photocatalytic activities

High adsorption capabilities and visible light photocatalytic activities of SnS₂ nanosheet-based microstructures are achieved.

Synthesis of three-dimensional AlN–Si3N4 branched heterostructures and their photoluminescence properties

Three-dimensional AlN–Si₃N₄ branched heterostructures are synthesized via extended vapor–liquid–solid and vapor–solid growth of one-dimensional Si₃N₄ nanostructures and AlN nanocones successively.