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PV technology offers a sustainable solution to the increased energy demand especially based on mono- and polycrystalline silicon solar cells. The most recent years have allowed the successful development of perovskite and tandem heterojunction Si-based solar cells with energy conversion efficiency over 28%. The metal oxide heterojunction tandem solar cells have a great potential application in the future photovoltaic field. Cu2O (band gap of 2.07 eV) and ZnO (band gap of 3.3 eV) are very good materials for solar cells and their features completely justify the high interest for the research of tandem heterojunction based on them. This review article analyzes high-efficiency silicon-based tandem heterojunction solar cells (HTSCs) with metal oxides. It is structured on six chapters dedicated to four main issues: (1) fabrication techniques and device architecture; (2) characterization of Cu2O and ZnO layers; (3) numerical modelling of Cu2O/ZnO HTSC; (4) stability and reliability approach. The device architecture establishes that the HTSC is constituted from two sub-cells: ZnO/Cu2O and c-Si. The four terminal tandem solar cells contribute to the increased current density and conversion efficiency. Cu2O and ZnO materials are defined as promising candidates for high-efficiency solar devices due to the morphological, structural, and optical characterization emphasized. Based on multiscale modelling of PV technology, the electrical and optical numerical modelling of the two sub-cells of HTSC are presented. At the same time, the thermal stability and reliability approach are essential and needed for an optimum operation of HTSC, concerning the cell lifetime and degradation degree. Further progress on flexible HTSC could determine that such advanced solar devices would become commercially sustainable in the near future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis and purification of dual emissive CDs and their extensive spectroscopic characterization. • Formulation of water-based flexo ink and study of ink properties. • Security printing and evaluation of print properties for anti-counterfeit applications. • Fabrication of biodegradable high-performance supercapacitor. Literature evidence reveals versatile applications of carbon dots (CDs), but generally mixtures of various types of carbon nanomaterials, molecular intermediates as well as side products are obtained upon hydrothermal treatment of the precursor material. This demands isolation of pure components and their complete characterization before these nano carbonaceous materials are chosen for suitable applications. In the present study, perylenetetracarboxylic dianhydride (PTCDA) is subjected to hydrothermal treatment and the mother liquor obtained is separated using column chromatography technique using dichloromethane-methanol solvent system to isolate fractions of various fluorescent carbonaceous nanostructures. The TEM imaging of nano carbonaceous particles of all five fractions indicated that the first and third fractions were composed of nanoribbons, while the latter two fractions largely contained quasi-spherical nanoparticles of both lesser (carbon quantum dots) and greater (carbon nanodots) than 10 nm dimensions. The XPS results of all the fractions suggested separation based on polarity difference. The I D /I G ratios obtained from Raman spectra implied the presence of several defects on the CDs. The time resolved fluorescence spectra of third, fourth and fifth fractions revealed mono-exponential decay of fluorophores with excitation independent average lifetime values. The fifth fraction exhibited good biocompatibility and the highest absolute fluorescence quantum yield of 58.47 % among all the isolated samples. As these CDs displayed a remarkable rise in the quantum yield to 88.60 % when dispersed in water, a water-based flexo-ink was formulated. The photostable pale yellow flexo print proofs obtained on UV dull paper exhibited a green fluorescence under 365 nm illumination, whereas a yellow glow when shined with blue light, which can serve as an authentication feature for security documents and currency notes. Moreover, as the third fraction constitutes mainly of carbon nanoribbons (CNRs), an optimized polymer electrolyte was prepared along with sodium alginate (SA), and MgCl 2 to understand their potential use in energy storage application. A supercapacitor was fabricated and tested for its electrochemical performance such as cyclic voltammtery (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge (GCD). An enhanced current window was observed in the CV of SA/CNRs compared to pure SA and SA/CNRs/Mg films, which indicated a structural interaction of CNRs with SA. The conductivity of SA/CNRs/Mg was lesser than SA/CNRs in EIS studies due to the presence of Mg ions, while pure SA showed lesser conductivity. The dual ionic interaction of Na and Mg along with enhanced structural stability due to doped CNRs favors its convenient supercapacitor application. The fabricated eco-friendly supercapacitor showed a specific capacitance of 84 F/g. The GCD of the device displayed pseudocapacitance behaviour and was quite stable for 2000 cycles with coulombic efficiency of 96 %. [ABSTRACT FROM AUTHOR]

• Photocatalytic geopolymer is an affordable solution for environmental pollution. • Synthesis methods for catalysts based on geopolymers are comprehensively outlined. • Various methods for characterizing freshly produced geopolymers are examined. • Circular economy, trends, and future of photocatalytic geopolymers are proposed. Photocatalytic geopolymers are a class of low-cost environmental remediation and sustainable construction materials. They garnered significant interest due to their unique synergistic combination of geopolymer technology and photocatalytic properties, offering a wealth of potential applications. This work provides a full review of various approaches to synthesis photocatalytic geopolymer, explores characterization techniques employed, and delves their efficiency as photocatalysts in organic pollutant photodegradation. The development of geopolymer photocatalytic materials involves the choice of appropriate aluminosilicate source material, activator solution and photocatalytically active compounds. Several techniques were used such as sol–gel, deep coated and hydrothermal methods. The review provides also a detailed overview of the characterization techniques employed to analyze the structural, morphological, and optical properties of photocatalytic geopolymers. Furthermore, this review focuses on the photocatalytic activity of geopolymers in the degradation of organic dye, elucidating the underlying mechanisms and degradation pathways involved. The impact of various photocatalytic parameters, such as catalyst composition, surface area and solution pH, has been highlighted with regard to the photocatalytic efficiency of geopolymers. Additionally, the review explores the challenges associated with the practical implementation of geopolymers as photocatalysts, including stability, reusability, and scale-up considerations. Future prospects and potential research directions in the field of geopolymers photocatalytic antibiotics photodegradation are also discussed. Overall, this review can serve as a guide for proposing, researching, and implementing photocatalytic geopolymers in the process of degrading organic pollutants present in diverse water sources. [ABSTRACT FROM AUTHOR]

Abstract As promising candidates for solar cell and photodetection applications in the range 1.0–1.16 eV, the growth of dilute nitride GaAsSbN alloys lattice matched to GaAs is studied. With this aim, we have taken advantage of the temperature gradient in the molecular beam epitaxy reactor to analyse the impact of temperature on the incorporation of Sb and N species according to the wafer radial composition gradients. The results from the combination of X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopies (EDS) show an opposite rate of incorporation between N and Sb as we move away from the centre of the wafer. A competitive behaviour between Sb and N in order to occupy the group-V position is observed that depends on the growth rate and the substrate temperature. The optical properties obtained by photoluminescence are discussed in the frame of the double-band anticrossing model. The growth conditions define two sets of different parameters for the energy level and the coupling interaction potential of N, which must be taken into account in the search for the optimum compositions 1–1.15-eV photonic applications.

Abstract In this work, ZnO-TiO 2 nanocomposites were synthesized using the polymerizable complex method. Their structural and optical characteristics were determined using IR, UV-Vis absorption and diffuse reflectance spectroscopies, X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence. The primary particles obtained were nanometric in size (<100 nm) with a spheroidal morphology. All the samples presented zincite as the main crystalline phase. On adding the titanium, the diffractograms indicating the formation of a solid solution. The doped ZnO samples, treated at 700 °C, also presented Zn 2 TiO 4. Independent of the heat treatment, the synthesized ZnO samples showed an energy gap value of ∼3.2 eV. In the case of ZnO-TiO 2 composites, treated at 500 °C, the gap value was of 3.28 eV (1% of Ti4+) and ∼3.2 eV (5% of Ti4+). The photoluminescence results indicated the presence of defects in the structure, mainly of V O , O i , Zn i and V Zn depending on the temperature of the heat treatment to which the sample is subjected. Graphical abstract Image 1 Highlights • - ZnO-TiO 2 nanocomposites have been successfully synthesized by wet-chemical method. • - Structure, morphology and optical properties of ZnO-TiO 2 nanocomposites were described. • - Photoluminescence spectra reiterated the existence of localized states in the gap related to defects such as V O , O i , Zn i and V Zn. [ABSTRACT FROM AUTHOR]

In this research, the Zn(C5H7O2)2·xH2O-based growth of ZnO micro/nanostructures in a low temperature, vapor-trapped chemical vapor deposition system was attempted to optimize structural and optical properties for potential biomedical applications. By trapping in-flow gas molecules and Zinc vapor inside a chamber tube by partially obstructing a chamber outlet, a high pressure condition can be achieved, and this experimental setup has the advantages of ease of synthesis, being a low temperature process, and cost effectiveness. Empirically, the growth process proceeded under a chamber condition of an atmospheric pressure of 730 torr, a controlled volume flow rate of input gas, N2/O2, of 500/500 Standard Cubic Centimeters per Minute (SCCM), and a designated oven temperature of 500 °C. Specifically, the dependence of structural and optical properties of the structures on growth duration and spatially dependent temperature were investigated utilizing scanning electron microscopy, X-ray diffraction (XRD), photoluminescence (PL), and ultraviolet-visible transmission spectroscopy. The experimental results indicate that the grown thin film observed with hexagonal structures and higher structural uniformity enables more prominent structural and optical signatures. XRD spectra present the dominant peaks along crystal planes of (002) and (101) as the main direction of crystallization. In addition, while the structures excited with laser wavelength of 325 nm emit a signature radiation around 380 nm, an ultraviolet lamp with a wavelength of 254 nm revealed distinctive photoluminescence peaks at 363.96 nm and 403.52 nm, elucidating different degrees of structural correlation as functions of growth duration and the spatial gradient of temperature. Transmittance spectra of the structures illustrate typical variation in the wavelength range of 200 nm to 400 nm, and its structural correlation is less significant when compared with PL. [ABSTRACT FROM AUTHOR]

As promising candidates for solar cell and photodetection applications in the range 1.0-1.16 eV, the growth of dilute nitride GaAsSbN alloys lattice matched to GaAs is studied. With this aim, we have taken advantage of the temperature gradient in the molecular beam epitaxy reactor to analyse the impact of temperature on the incorporation of Sb and N species according to the wafer radial composition gradients. The results from the combination of X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopies (EDS) show an opposite rate of incorporation between N and Sb as we move away from the centre of the wafer. A competitive behaviour between Sb and N in order to occupy the group-V position is observed that depends on the growth rate and the substrate temperature. The optical properties obtained by photoluminescence are discussed in the frame of the double-band anticrossing model. The growth conditions define two sets of different parameters for the energy level and the coupling interaction potential of N, which must be taken into account in the search for the optimum compositions 1-1.15-eV photonic applications. [ABSTRACT FROM AUTHOR]

Abstract: This Letter reports on structural and photoluminescence properties of Zn1− x Mn x O nanocrystalline powders, which were synthesized by using oxalate precursor decomposition method. From the XRD features, we have noticed that all samples exhibit wurtzite crystal structure. The origin of photoluminescence properties of Mn doped and undoped ZnO have been discussed. [Copyright &y& Elsevier]

The ternary compound semiconductor CuInS2 is one of the most attractive materials for high efficiency solar cells due to its bandgap of 1.55 eV which is well matched to the solar spectrum. We deposit CuInS2 films on float glass substrates by a reactive RF sputter process using a Cu-In alloy target and H2S gas. By optimizing the sputter parameters, such as the sputter power, temperature of the substrate, and the flow of H2S, high quality films were obtained. The surface morphology, phase structure and composition of the layers were analyzed by atomic force microscopy (AFM), X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX) and Rutherford backscattering spectroscopy (RBS), respectively. The electrical properties of the films were characterized by Hall effect measurements. photoluminescence (PL) and transmission measurements were performed to examine the optical properties of the films, and the absorption coefficients and the direct band gap of the films were evaluated by transmission measurements. [Copyright &y& Elsevier]

The diffraction efficiencies of modified sinusoidal and blazed gratings are investigated in the high spatial frequency regime by rigorous numerical methods and are compared to experimentally manufactured gratings. The introduced modifications take actual technological induced variations of the profile geometries, such as specific corner rounding, into account. The high spatial frequency regime (resonance regime) is characterized by a local grating period, g, to wavelength, λ, ratio of 0.7 ≤ g/λ ≤ 4 and shows an important relevance for applications in spectroscopy and diffractive imaging. The investigations are carried out for both reflection on metallic surfaces and transmission of dielectric structures over a broad range of grating periods and incidence angles. It was found that near the grating resonance, the more simply producible sine gratings can compete in diffraction efficiency with sawtooth structures. Additionally, for certain application conditions, holographically modified sine structures achieve higher efficiencies than the ideal sine profile. It is also shown that holographic sinusoidal-like profiles measured by AFM can be fitted to a super-Gaussian shape, which is then used to inversely reconstruct the structure profiles from efficiency data.