Thin film CdZnS/CuInSe2 solar cells by spray pyrolysis

Cd_1−xZn_xS/CuInSe₂ solar cells having efficiencies in the range of 2·3% were fabricated by spray pyrolysis. The best cell had the following parameters:V _oc = 305 mV,J _sc = 32 mA/cm², FF = 0·32 area = 0·4 cm² and efficiency = 3·149%.V _oc versus temperature measurements showed that the electron affinity difference was 0·22 eV. Forward dark current versus voltage curves were plotted and a possible current mechanism occurring in these cells has been proposed.     

High-energy emission band nature in ZnS-type phosphors activated with silver and chlorine

The cathodoluminescence emission spectra of cubic blue-emitting ZnS:Ag, Cl, hexagonal green-emitting (Zn_0.675, Cd_0.325) S:Ag, Cl as well as hexagonal red-emitting (Zn_0.27, Cd_0.73) S:Ag, Cl phosphors have been measured at 293, 77 and 4.2 K. The measured spectra of the phosphors exhibited a single broad emission band at 293 K, while they had two emission bands at 77 and 4.2 K. The two emission bands shifted to a lower energy with increase of their corresponding half-widths as the temperature at which the spectra were measured was raised. The time-resolved emission spectra measured showed that the low-energy band also shifted in the lower energy direction during the decay of luminescence, confirming its donor-acceptor (DA) transition nature. The high-energy band decayed faster than the low-energy one and no energy shift occurred during its decay; it was attributed to donor-isoelectronic pair (DI) transition. The lifetimes of 0.625 and 4.2 µsec were estimated for high- and low-energy bands, respectively, in the emission spectra of ZnS:Ag, Cl at 4.2 K.     

Controllable preparation and efficient visible-light-driven photocatalytic removal of Cr(VI) using optimized Cd0.5Zn0.5S nanoparticles decorated H-Titanate nanotubes

Based on one-dimensional (1D) H-titanate nanotubes (H-TNTs: TNTs with loosely distributed H⁺ across the interlayers), a novel series of Cd_0.5Zn_0.5S loaded H-TNTs (Cd_0.5Zn_0.5S/TNTs) composites with varied ratios have been achieved by the in-situ growth method. The as-prepared samples were characterized by (high-resolution) transmission electron microscopy (HR/TEM), XRD, FT-IR, XPS, UV–vis diffuse reflectance spectroscopy (UV–vis DRS), fluorescence spectroscopy (FL), photocurrent, electron spin resonance (ESR) spectroscopy, etc. These studies concurrently revealed a successful formation of Cd_0.5Zn_0.5S/TNTs heterojunction, and a homogeneous distribution of Cd_0.5Zn_0.5S nanoparticles over the surface of 1D H-TNTs. The incorporation of the appropriate amount of Cd_0.5Zn_0.5S nanoparticles (10%) significantly improves the efficiency of photogenerated electron-hole pairs separation. The photocatalytic reduction efficiency of the Cd_0.5Zn_0.5S/TNTs for Cr(VI) and degradation efficiency for organic molecules increased initially and then decreased with the amount of loaded Cd_0.5Zn_0.5S nanoparticles. The optimal photocatalytic efficiency was observed at 10 %Cd_0.5Zn_0.5S/TNTs, which were 2.71-fold and 4.8-fold than that of pure H-TNTs for the removal of the Cr(VI) and the degradation of the organic molecules, respectively. The ESR test signified that the holes (h⁺) and superoxide radicals (∙O₂^–) played an essential role in the degradation process of organic molecules. Finally, a reasonable explanation for enhanced photocatalysis performance was proposed.     

Features of the influence of the deposition power and Ar/O2 gas ratio on the microstructure and optical properties of the Zn0.9Cd0.1O films

The Zn_0.9Cd_0.1O films have been prepared using the direct current (dc) reactive magnetron sputtering technique under the different ratios of Ar/O₂. We have studied the effects of the different gas concentrations (Ar/O₂) and the deposition powers on a crystal structure, a surface morphology, and optical properties of the Zn_0.9Cd_0.1O films. The surface and the structure investigations have shown a strong influence of the growth conditions on the film microstructure. The structural analysis revealed that all grown films are polycrystalline and single-phase. It was found that increasing the argon concentration leads to an improvement of the structural quality of the Zn_0.9Cd_0.1O films. The features of controlling the band gap and the surface morphology of the Zn_0.9Cd_0.1O ternary alloys by changing the growth parameters have been discussed.     

Electrical properties of Cd1−x, ZnxS liquid junction cells

Semiconductor-liquid junction cells with simple design are formed with Cd_(1?x), Zn_x S film electrodes deposited by a chemical bath deposition technique. The electrical properties of these cells are studied and the influence of the zinc composition x in Cd_(1?x), Zn_x S electrodes and the intensity of illumination on cell characteristics are discussed. Speed of response and photo-response of the cells are also reported.     

Electrodepositions of CdS,ZnS and Cd1-xZnxS films

Thin films of CdS, ZnS and Cd_1-xZn_xS, (0< x<1) have been electrodeposited from acidic bath using CdSO₄, ZnSO₄ and Na₂S₂O₃ at pH between 2 to 2.5 onto different substrates. The structural and optical properties of these films have been studied. It was found that CdS, ZnS and Cd_1-x Zn_x S film could be electrodeposited from acidic bath. The XRD patterns showed that the films consist of mixed phases of CdS and ZnS with presence of free Cd, Zn and S. The optical properties showed that bandgaps of CdS and ZnS are 2.4 and 3.55 eV respectively. The bandgaps of Cd_1-x Zn_x S films varied between 2.4 to 3.55 eV, depending upon Zn content in the film.     

Optical properties of Cd1−xZnxS thin films for CuInGaSe2 solar cell application

The photovoltaic Cd_1−xZn_xS thin films, fabricated by chemical bath deposition, were successfully used as n-type buffer layer in CuInGaSe₂ (CIGS) solar cells. Comprehensive optical properties of the Cd_1−xZn_xS thin films were measured and modeled by spectroscopic ellipsometry (SE), which is proven to be an excellent and non-destructive technique to determine optical properties of thin films. The optical band gap of Cd_1−xZn_xS thin films can be tuned from 2.43 eV to 3.25 eV by controlling the Zn content (x) and deposition conditions. The wider-band-gap Cd_1−xZn_xS film was found to be favorable to improve the quantum efficiency in the wavelength range of 450-550 nm, resulting in an increase of short-circuits current for solar cells. From the characterization of quantum efficiency (QE) and current-voltage curve (J-V) of CIGS cells, the Cd_1−xZn_xS films (x = 0.32, 0.45) were demonstrated to significantly enhance the photovoltaic performance of CIGS solar cell. The highest efficiency (10.5%) of CIGS solar cell was obtained using a dense and homogenous Cd_0.68Zn_0.32S thin film as the buffer layer.     

Phase Relations in the Zn3As2–ZnAs2–CdAs2–Cd3As2 System

Phase relations along the Cd₃As₂–ZnAs₂ and Zn₃As₂–CdAs₂ joins are studied by differential thermal analysis, x-ray diffraction, and microstructural analysis. The results, in conjunction with earlier data on the CdAs₂–ZnAs₂, Zn₃As₂–Cd₃As₂, Cd₃As₂–CdAs₂, and ZnAs₂–Zn₃As₂ binaries, are used to map out the phase diagram of the liquidus surface in the composition region Zn₃As₂–ZnAs₂–CdAs₂–Cd₃As₂ of the ternary system Cd–As–Zn. The ternary eutectic revealed in this region has an approximate composition of 26 at. % Cd + 65 at. % As + 9 at. % Zn and melts at 863 K.     

Photoluminescence characteristics of synthesized copper doped Cd1−x Zn x S quantum dots

Free standing powders of copper-doped Cd_1?x Zn _x S (0 ≤ x ≤ 0.5) quantum dots (QDs) were synthesized using a simple chemical co-precipitation method. The copper concentration was varied from 0.01 to 10 at. wt% of Cd²⁺. X-ray diffraction and transmission electron microscope were used for crystallographic and morphological analyzes. Room temperature time resolved luminescence spectra were recorded using high peak power, pulsed N₂-laser excitation. Decay time values for bluish green and yellow emission have been calculated from recorded luminescence decay curves. Decay time dependence on Cu²⁺ and Zn²⁺ concentrations have been studied in detail. These QDs will have wide applications as nanophosphors, solar cells, photocatalysts and chemical sensors.     

Band alignment of Cd(1 − x)ZnxS produced by spray pyrolysis method

Cd_(1 − x)Zn_xS thin films have been grown on glass substrates by the spray pyrolysis method using CdCl₂ (0.05 M), ZnCl₂ (0.05 M) and H₂NCSNH₂ (0.05 M) solutions and a substrate temperature of 260 °C. The energy band gap, which depends on the mole fraction × in the spray solution used for preparing the Cd_(1 − x)Zn_xS thin films, was determined. The energy band gaps of CdS and ZnS were determined from absorbance measurements in the visible range as 2.445 eV and 3.75 eV, respectively, using Tauc theory. On the other hand, the values calculated using Elliott-Toyozawa theory were 2.486 eV and 3.87 eV, respectively. The exciton binding energies of Cd_0.8Zn_0.2S and ZnS determined using Elliott-Toyozawa theory were 38 meV and 40 meV, respectively. X-ray diffraction results showed that the Cd_(1 − x)Zn_xS thin films formed were polycrystalline with hexagonal grain structure. Atomic force microscopy studies showed that the surface roughness of the Cd_(1 − x)Zn_xS thin films was about 50 nm. Grain sizes of the Cd_(1 − x)Zn_xS thin films varied between 100 and 760 nm.     

Ethylenediamine-assisted solvothermal synthesis of one-dimensional CdxZn(1−x)S solid solutions and their photocatalytic activity for nitrobenzene reduction

A series of one-dimensional Cd_xZn_(1−x)S semiconductor alloys were prepared via a hydrothermal method with the assistance of ethylenediamine at 180 °C for 12 h. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption/desorption and Fourier transform infrared techniques. With the value of x increased, the band gap of Cd_xZn_(1−x)S semiconductor alloys gradually decreased indicating that catalysts were exchanged to visible-light response. Photocatalytic reduction results showed that Cd_0.73Zn_0.27S exhibited the highest photocatalytic activity toward photo production of aniline via nitrobenzene reduction under visible irradiation respectively. The reaction mechanism was also discussed.     

Study of electrical and optical properties of Cd1 − x Zn x S thin films

Thin films of Cd_0.9Zn_0.1S and CdS were prepared by thermal evaporation under vacuum of 10^–6 Torr and with deposition rate of 60 nm/min. X ray diffraction studies confirm the hexagonal structure of both CdS and Cd_0.9Zn_0.1S films. The effect of heat treatments with or without CdCl₂ enhances the grain size growth and improves the crystalline of the films. Moreover, the activation energy is decreased by heat treatment with or without CdCl₂ for all thin films. The optical absorption coefficient of Cd_0.9Zn_0.1S thin films were determined from measured transmittance and reflectance in the wavelength range of 300 to 2500 nm. The optical absorption spectra reveal the existence of direct energy gap for these films. It was found that the optical energy gap decreases upon annealing or CdCl₂ treatments.     

Ethanol-thermal synthesis of Cd1−xZnxS nanoparticles with enhanced photodegradation of 4-chlorophenol

Cd_1−xZn_xS nanoparticles were prepared by a one-pot solvothermal process from Zn(CH₃COO)₂, Cd(CH₃COO)₂ and NaS₂CNEt₂·3H₂O (sodium diethyldithiocarbamate, DDTC). The Cd_1−xZn_xS nanoparticles were characterized by X-ray powder diffraction, transmission electron microscope and high-resolution transmission electron microscope equipped with an energy-dispersive X-ray spectrometer. The absorption spectra of the Cd_1−xZn_xS nanoparticles can be tuned into visible region by modulating stoichiometric ratio between Zn and Cd. With the increase of Zn content, the Cd_1−xZn_xS nanoparticles showed an enhanced photocatalytic activity on degradation of 4-chlorophenol. The Cd_1−xZn_xS prepared under the optimal experimental condition (initial Zn/Cd = 3:1, 210 °C, 24 h, in ethanol) possessed the best photocatalytic activity. The conversion ratio could reach up to 84% after 12 h under irradiation of visible light for Cd_1−xZn_xS prepared in ethanol, which was obviously superior to those of products prepared in water. These results showed that both crystallinity and synthetic medium were responsible for the enhanced photocatalytic activity for 4-chlorophenol.     

Formation of cadmium chlorides via cadmium dissolution in chloride melts

The kinetics and mechanism of the formation of complex Cd(I) ions via the reaction of metallic cadmium with Cd²⁺ ions in the Cd⁰-CdCl₂-ZnCl₂-NH₄Cl system are studied spectroscopically. The formation of Cd ₂ ²⁺ and Cd ₂ ³⁺ is evidenced by absorption bands around 270 and 335 nm, respectively, in the electronic spectrum of the melt. The anode current efficiency is determined for cadmium electrorefining in a chloride melt. A mechanism is proposed for the anodic dissolution of cadmium at different current densities and process temperatures.     

NiS/Cd0.6Zn0.4S Schottky Junction Bifunctional Photocatalyst for Sunlight-Driven Highly Selective Catalytic Oxidation of Vanillyl Alcohol Towards Vanillin Coupled with Hydrogen Evolution Reaction

Selective oxidation of biomass-based molecules to high-value chemicals in conjunction with hydrogen evolution reaction (HER) is an innovative photocatalysis strategy. The key challenge is to design bifunctional photocatalysts with suitable band structures, which can achieve highly efficient generation of high-value chemicals and hydrogen. Herein, NiS/Cd_0.6Zn_0.4S Schottky junction bifunctional catalysts are constructed for sunlight-driven catalytic vanillyl alcohol (VAL) selective oxidation towards vanillin (VN) coupling HER. At optimal conditions, the 8% NiS/Cd_0.6Zn_0.4S photocatalyst achieves high activity of VN production (3.75 mmol g⁻¹ h⁻¹) and HER (3.84 mmol g⁻¹ h⁻¹). It also exhibits remarkable VAL conversion (66.9%), VN yield (52.1%), and selectivity (77.8%). The photocatalytic oxidation of VAL proceeds a carbon-centered radical mechanism via the cleavage of α_C–H bond. Experimental results and theoretical calculations show that NiS with metallic properties enhances the electron transfer capability. Importantly, a Ni-S-Cd “electron bridge” formed at the interface of NiS/Cd_0.6Zn_0.4S further improves the separation/transfer of electrone/h⁺ pairs and also furnishes HER active sites due to its smaller the |ΔG_H*| value, thereby resulting in a remarkably HER activity. This work sheds new light on the selective catalytic oxidation VAL to VN coupling HER, with a new pathway towards achieving its efficient HER efficiency.     

Unique 1D Cd1−xZnxS@O‐MoS2/NiOx Nanohybrids: Highly Efficient Visible‐Light‐Driven Photocatalytic Hydrogen Evolution via Integrated Structural Regulation

Development of noble‐metal‐free photocatalysts for highly efficient sunlight‐driven water splitting is of great interest. Nevertheless, for the photocatalytic H₂ evolution reaction (HER), the integrated regulation study on morphology, electronic band structures, and surface active sites of catalyst is still minimal up to now. Herein, well‐defined 1D Cd_1?xZn_xS@O‐MoS₂/NiO_x hybrid nanostructures with enhanced activity and stability for photocatalytic HER are prepared. Interestingly, the band alignments, exposure of active sites, and interfacial charge separation of Cd_1?xZn_xS@O‐MoS₂/NiO_x are optimized by tuning the Zn‐doping content as well as the growth of defect‐rich O‐MoS₂ layer and NiO_x nanoparticles, which endow the hybrids with excellent HER performances. Specifically, the visible‐light‐driven (>420 nm) HER activity of Cd_1?xZn_xS@O‐MoS₂/NiO_x with 15% Zn‐doping and 0.2 wt% O‐MoS₂ (CZ_0.15S‐0.2M‐NiO_x) in lactic acid solution (66.08 mmol h^?1 g^?1) is about 25 times that of Pt loaded CZ_0.15S, which is further increased to 223.17 mmol h^?1 g^?1 when using Na₂S/Na₂SO₃ as the sacrificial agent. Meanwhile, in Na₂S/Na₂SO₃ solution, the CZ_0.15S‐0.2M‐NiO_x sample demonstrates an apparent quantum yield of 64.1% at 420 nm and a good stability for HER under long‐time illumination. The results presented in this work can be valuable inspirations for the exploitation of advanced materials for energy‐related applications.     

A robust and self-assembled route to synthesis of CdZn(Se<Subscript>1−x</Subscript>Te<Subscript>x</Subscript>)<Subscript>2</Subscript> photoanodes as light harvesters for photoelectrochemical solar cells

This work reports on the development of CdZn(Se_1?xTe_x)₂ thin films utilized as the photoanode for photoelectrochemical cells (PECs). It was found that the incorporation of tellurium plays an important role in determining the optostructural, morphological, compositional and PEC performance of thin films. XRD measurements showed that the deposited thin films are in the mixed phases with a nanocrystalline nature. SEM images indicated that the surface morphology is favourable for effective light absorption in the solar spectrum. The EDS spectrum confirmed that thin film deposition occured in a stoichiometric manner. A detailed quantitative study was also executed using XPS and revealed the presence of Cd²⁺, Zn²⁺, Se^2? and Te^2? elements in the deposited thin film. Finally, the deposited thin films were tested for their photoelectrochemical (PEC) performance. The PEC study illustrated that CdZn(Se_1?xTe_x)₂ thin film showed the highest power conversion efficiency (η) of 1.13% among reported values.     

Conductivity compensation in CdZnTe: Cl crystals with variable zinc content

The effect of cadmium vapor pressure during postgrowth annealing on the compensation of conductivity has been studied in semi-insulating Cd_1?x Zn _x Te:Cl crystals with variable zinc content (x = 0.005, 0.01, and 0.05), which are used in nuclear radiation detectors. At a small zinc content (x = 0.005 and 0.01), the main role in the in Cd_1?x Zn _x Te:Cl crystals is played by the cadmium point defects. In crystals with a higher zinc content (x = 0.05), the compensation of charged defects is incompletely controlled by changing the cadmium vapor pressure, which is evidence of a significant influence of the zinc point defects.     

ZnxCd1 − xS as a heterojunction partner for CuIn1 − xGaxS2 thin film solar cells

Zinc cadmium sulfide (Zn_xCd_1 − xS) heterojunction partner layer prepared with chemical bath deposition (CBD) has exhibited better blue photon response and higher current densities due to its higher bandgap than that of conventional cadmium sulfide (CdS) layer for CuIn_1 − xGa_xS₂ (CIGS2) solar cells. CIGS2/Zn_xCd_1 − xS devices have also shown higher open circuit voltage, V_oc indicating improved junction properties. A conduction band offset has been observed by J-V curves at various temperatures indicating that still higher V_oc can be obtained by optimizing the conduction band offset. This contribution discusses the effect of variation of parameters such as concentration of compounds, pH of solution and deposition time during CBD on device properties and composition and crystallinity of film. Efficiencies comparable to CIGS2/CdS devices have been achieved for CIGS2/Zn_xCd_1 − xS devices.     

Structural and electronic properties of CdTe:Cl from first-principles

The structural and electronic properties of the dominant intrinsic defect of the Cd vacancy (V_Cd) and the Cl impurity in CdTe are studied using density functional theory. V_Cd is calculated to be a shallow double acceptor. Cl will substitute Te site (Cl_Te) and then act as a shallow donor in CdTe. Moreover, Cl_Te can bond with V_Cd, forming the defect complexes of Cl_Te–V_Cd. Cl_Te−V_Cd is a shallower acceptor than that of V_Cd. The defect complexes of (Cl_Te−V_Cd)⁻¹ can improve the p-doping behavior of CdTe.