Influence of copper concentration on sprayed CZTS thin films deposited at high temperature

In this study, Cu₂ZnSnS₄ (CZTS) thin films were deposited by spray pyrolysis technique at constant substrate temperature. The effects of the copper concentration on the structural, morphological and optical properties of the films were investigated. The copper concentration was varied from 0.15 to 0.25 M in the steps of 0.05 M. The structural studies revealed that the Cu poor film shows low intense peaks, but as Cu concentration increases a relatively more intense and sharper diffraction peaks (112), (200), (220), and (312) of the kesterite crystal structure were observed. Raman spectroscopy analysis confirmed the formation of phase-pure CZTS films. From the morphological studies, it is found that the grain size increased as the Cu concentration increases from 0.15 to 0.25 M. The optical band-gap values were estimated to be 1.61, 1.52 and 1.45 eV for copper concentration 0.15, 0.20 and 0.25 M, respectively. Photoelectrochemical cells using films of different copper concentrations were fabricated and the best cell exhibited an efficiency of 1.09% for 0.25 M of copper concentration.     

Effects of the sulfurization temperature on sol gel-processed Cu2ZnSnS4 thin films

As a promising and alternative solar absorber material, the copper–zinc–tin–sulfide compound (Cu₂ZnSnS₄) has been drawing attention in recent years for the production of cheap thin-film solar cells owing to the high natural abundance and non-toxicity of all the constituents, a tunable direct-band-gap energy and a large optical absorption coefficient. In addition, to overcome the problem of expensive vacuum-based methods, solution-based approaches are being developed for Cu₂ZnSnS₄ deposition. In this study, we have produced Cu₂ZnSnS₄ thin films via the sol–gel technique and subsequent sulfurization. The effects of the sulfurization temperature on the structural, morphological, compositional and optical properties of the films were investigated. X-ray diffraction and Raman spectroscopy analyses confirmed the formation of phase-pure CZTS films. The crystallinity of the films increased with an increasing sulfurization temperature. From the surface images and the results of the composition analysis, it was found that the films are uniform, composed of homogenously distributed grains and have compositions with Cu deficit. The values of the optical absorption coefficients for the films were found to be 10⁴ cm^?1 based on absorbance spectroscopy. The optical band-gap values were estimated to be between 1.32 and 2.27 eV depending on the sulfurization temperature.     

Facile mechano-chemical synthesis and enhanced photocatalytic performance of Cu2ZnSnS4 nanopowder

In the present study, Cu₂ZnSnS₄ (CZTS) powder was synthesized by the mechano-chemical method from its elemental constituents. X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and diffusion reflectance spectroscopy (DRS) were used for characterization of structural, morphological and optical properties. XRD result confirmed that a highly crystalline CZTS phase corresponding to the kesterite structure was formed after 50 h ball milling. Raman analysis confirmed the existence of single phase CZTS without any other phases. FESEM and TEM images reveal the irregular CZTS nanoparticles with an average size of 90 nm. The elemental mapping of the CZTS nanopowder showed the uniform distribution in agreement with the stoichiometry. DRS result showed a band gap value of 1.53 eV. XPS result revealed the oxidation states as Cu⁺, Zn²⁺, Sn⁴⁺ and S²⁻. The photocatalytic activity of CZTS has been investigated through photodegradation of methylene blue (MB) and methyl orange (MO) dyes solution with different concentrations under visible light irradiation. Although the CZTS decomposed MO only 81% until 210 min, the MB solution was completely photodegraded after 100 min. A kinetic study by Langmuir-Hinshelwood (L-H) model indicated about 3.7 times faster degradation of MB than MO and also higher adsorption capacity for MB by CZTS. Furthermore, the prepared CZTS was reusable and can be repeatedly used for the removal of dyes from aqueous solutions.     

Growth and properties of Cu3SbS4 thin films prepared by a two-stage process for solar cell applications

Cu₃SbS₄ is a promising material for thin film heterojunction solar cells owing to its suitable optical and electrical properties. In this paper, we report the preparation of Cu₃SbS₄ thin films by annealing the Sb₂S₃/CuS stacks, produced by chemical bath deposition, in a graphite box held at different temperatures. The influence of annealing temperature on the growth and properties of these films is investigated. These films are systematically analyzed by evaluating their structural, microstructural, optical and electrical properties using suitable characterization techniques. X-ray diffraction analysis showed that these films exhibit tetragonal crystal structure with the lattice parameters a=0.537 nm and b=1.087 nm. Their crystallite size increases with increasing annealing temperature of the stacks. Raman spectroscopy analysis of these films exhibited modes at 132, 247, 273, 317, 344, 358 and 635 cm⁻¹ due to Cu₃SbS₄ phase. X-ray photoelectron spectroscopy analysis revealed that the films prepared by annealing the stack at 350 °C exhibit a Cu-poor and Sb-rich composition with +1, +5 and −2 oxidation states of Cu, Sb and S, respectively. Morphological studies showed an improvement in the grain size of the films on increasing the annealing temperature. The direct optical band gap of these films was in the range of 0.82–0.85 eV. Hall measurements showed that the films are p-type in nature and their electrical resistivity, hole mobility and hole concentration are in the ranges of 0.14–1.20 Ω-cm, 0.05–2.11 cm² V⁻¹ s⁻¹ and 9.4×10²⁰–1.4×10¹⁹ cm⁻³, respectively. These structural, morphological, optical and electrical properties suggest that Cu₃SbS₄ could be used as an absorber layer for bottom cell in multi-junction solar cells.     

Single step electrosynthesis of Cu2ZnSnS4 (CZTS) thin films for solar cell application

The Cu₂ZnSnS₄ (CZTS) thin films have been electrodeposited onto the Mo coated and ITO glass substrates, in potentiostatic mode at room temperature. The deposition mechanism of the CZTS thin film has been studied using electrochemical techniques like cyclic voltammetery. For the synthesis of these CZTS films, tri-sodium citrate and tartaric acid were used as complexing agents in precursor solution. The structural, morphological, compositional, and optical properties of the CZTS thin films have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), EDAX and optical absorption techniques respectively. These properties are found to be strongly dependent on the post-annealing treatment. The polycrystalline CZTS thin films with kieserite crystal structure have been obtained after annealing as-deposited thin films at 550 in Ar atmosphere for 1 h. The electrosynthesized CZTS film exhibits a quite smooth, uniform and dense topography. EDAX study reveals that the deposited thin films are nearly stoichiometric. The direct band gap energy for the CZTS thin films is found to be about 1.50 eV. The photoelectrochemical (PEC) characterization showed that the annealed CZTS thin films are photoactive.     

A Promising Modified SILAR Sequence for the Synthesis of Photoelectrochemically Active Cu2ZnSnS4 (CZTS) Thin Films

A promising modified SILAR sequence approach has been employed for the synthesis of photoelectrochemically active Cu₂ZnSnS₄ (CZTS) thin films. To study the influence of sulfurization temperatures on the CZTS thin films, the CZTS precursor thin films were annealed at temperatures of 520, 540, 560, and 580 °C for 1 h in an H₂S (5 %)+Ar (95 %) atmosphere. These films were characterized for their structural, morphological, and optical properties using X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, and UV-vis spectrophotometer techniques. The film sulfurized at an optimized temperature of 580 °C shows the formation of a prominent CZTS phase with a dense microstructure and optical band gap energy of 1.38 eV. The photoelectrochemical (PEC) device fabricated using optimized CZTS thin films sulfurized at 580 °C exhibits an open circuit voltage (V_oc) of 0.38 V and a short circuit current density (J_sc) of 6.49 mA cm⁻², with a power conversion efficiency (η) of 0.96 %.     

Cu2ZnSnS4 as a hole-transport layer in triple-cation perovskite solar cells: Current density versus layer thickness

Cu₂ZnSnS₄ (CZTS) is a good candidate for cost-effective perovskite solar cells (PSCs) due to its direct bandgap with a value of 1.4–1.5 eV. In this study, we investigate CZTS ink as an inorganic hole-transport-layer (HTL) in CsMAFAPbIBr mixed halide PSCs. We study the cell efficiency and hole extraction from the perovskite layer for different thicknesses of HTL. The optimized device exhibits better hole selectivity, and the best efficiency of the device (12.84%) is achieved for the CZTS layer with a thickness of 159 nm. The prepared samples were also tested by open-circuit voltage decay analysis and electrochemical impedance spectroscopies. Results show that the optimized device effectively prohibits the electrons-holes recombination with a charge transfer resistance of 9.38 Ω cm². This work suggests that the optimal thickness of CZTS as an HTL in triple-cation PSC is about 159 nm by giving short-circuit current density of 23.69 mA cm^?2.     

The role of sulphur in the sulfurization of CZTS layer prepared by DC magnetron sputtering from a single quaternary ceramic target

The influence of sulphur vapour pressure, controlled by its mass, on the grain growth and optoelectronic properties of Cu₂ZnSnS₄ (CZTS) films prepared by a two-step procedure based on sputtering was studied. It was found that both the crystallinity and grain size of the films were promoted with the increase of the sulphur vapour pressure, indicating that the crystal growth was controlled by the sulphur vapour pressure. In addition, the crystal growth process of CZTS was investigated by analysing the microstructure and elemental composition of the sulfurized films with different masses of sulphur. It was also found that the content of Sn in the sulfurized films decreased after high-temperature annealing. However, the second phase SnS₂ was observed on the sample surface, which led to the increase of the optical band gap of the film. Moreover, we proposed the regulatory mechanism of sulphur vapour pressure in the grain growth of CZTS film. Finally, a highly crystalline p-type kieserite Cu₂ZnSnS₄ film with carrier concentration of 8.16?×?10¹⁷ cm^?3, mobility of 1.24?cm²/V?s and optical bandgap of 1.54?eV was obtained. This CZTS layers are expected to fabricate high efficiency thin film solar cells.     

Cu2ZnSnS4 nanoparticles synthesized via reaction media with glycine

Single-phase kesterite Cu₂ZnSnS₄ (CZTS) nanoparticles, with spherical-like shape and average sizes of 3 nm, were synthesized by a novel aqueous route in which glycine molecules had two crucial roles. The first one was to promote the gradual release of Cu⁺ and Zn²⁺ ions from their respective complexes. The other role is to act as a capping agent to control the growth of the nanoparticles and aggregation. The reaction and growth mechanisms were discussed in relation to the reactants' nature, studies of the crystalline structure and morphology of the CZTS nanoparticles. Inks were prepared with the precipitated nanoparticles to fabricate films on fused-silica substrates by the combining the doctor Blade technique and axial compression. Analysis of CZTS film, annealed at the temperature of 500 °C in Ar-atmosphere, proved micron-sized particles’ formation with improved crystallinity. Optical studies revealed that both nanoparticles and films exhibit broad absorption edges extending to the near-infrared. The bandgap energy values of the developed materials are in the range of 1.41–1.45 eV.     

Structural,optical and electrical properties of indium doped Cu2ZnSn(S,Se)4 thin films synthesized by the DC and RF reactive magnetron cosputtering

Element doping into the Cu₂ZnSn(S,Se)₄ (CZTSSe) absorber is an effective method to optimize the performance of thin film solar cells. In this study, the Cu₂In_xZn_1-xSn(S,Se)₄ (CIZTSSe) precursor film was deposited by magnetron cosputtering technique using indium (In) and quaternary Cu₂ZnSnS₄ (CZTS) as targets. Meanwhile, the In content was controlled using the direct current (DC) power on In target (P_In). A single kesterite CIZTSSe alloy was formed by successfully doping a small number of In³⁺ into the main lattice of CZTSSe. The partial Zn²⁺ cations were substituted by In³⁺ ions, resulting in improving properties of CZTSSe films. Morphological analysis showed that large grain CIZTSSe films could be obtained by doping In. The well-distributed, smooth, and dense film was obtained when the P_In was 30 W. The band gap of CIZTSSe could be continuously adjusted from 1.27 to 1.05 eV as P_In increased from 0 to 40 W. In addition, the CIZTSSe alloy thin film at P_In = 30 W exhibited the best p-type conductivity with Hall mobility of 6.87 cm²V^?1s^?1, which is a potential material as the absorption layer of high-performance solar cells.     

The effect of the Zn/Sn ratio on the formation of single phase kesterite Cu2ZnSnS4 solar cell material

The effect of the Zn/Sn ratio in the solution on the properties of Cu₂ZnSnS₄ films prepared by sol-gel method has been investigated. As the Zn/Sn ratio in the solution increases to a certain value, a pure single phase kesterite CZTS is obtained and confirmed by XRD, XPS and Raman. Through controlling the Zn/Sn ratio in the solution, secondary phases such as SnO₂ can be avoided and an optimal condition for single phase kesterite CZTS can be achieved. Surface SEM images of the CZTS films are investigated and the optical band gap of the optimized CZTS film is found to be 1.23 eV.     

Dispersive optical constants and electrical properties of nanocrystalline CuInS2 thin films prepared by chemical spray pyrolysis

Nanocrystalline CuInS₂ thin films were deposited on borosilicate glass substrates via chemical spray pyrolysis method. The structural, morphological, optical, and electrical properties were studied as a function of increasing annealing temperature from 250 to 350 ̊C. XRD analysis showed mixed phases at lower temperatures with the preferred orientation shifting towards the (112) chalcopyrite CuInS₂ plane at higher substrate temperature. The crystallite size increased slightly between 13 and 18 nm with increase in annealing temperature. The optical band gap was determined on basis of Tauc extrapolation method and the Wemple–Di-Domenico single oscillator model. Possible structural and quantum confinement effect may have resulted in relatively larger band gaps of 1.67–2.04 eV, relative to the bulk value of 1.5 eV. The presence of Cu_xS in the as-deposited and wurtzite peaks after annealing at 350 ^̊C play a role in influencing the optical and electrical properties of CuInS₂ thin films.     

Distribution of relaxation time in solution-processed polycrystalline CZTS thin films: Study of impedance spectroscopy

Here we report the complex impedance spectroscopic analysis of polycrystalline CZTS thin films synthesized by sol-gel spin coating technique without any post deposition sulphurization. The films are characterized by microstructural, compositional, optical and electrical studies to confirm the formation of kesterite phase of CZTS comprises of well distributed compact grains with the optical band gap 1.44?eV. Room temperature electrical characterizations of the CZTS thin films by four-probe and Hall effect technique revealed the p-type conductivity of the films with resistivity ~ 1.45?×?10^?2 Ω?cm, mobility ~ 3.7?×?10³ cm² V^?1 s^?1 and carrier concentration ~ 1.82?×?10¹⁷ cm^?3. The distribution of relaxation time (DRT) function with improved frequency resolution is reconstructed from the impedance spectra of CZTS film recorded in the frequency range 50?Hz to 5?MHz at room temperature to identify the number of electrical processes in the polycrystalline film. The Nyquist plot is fitted into electrical model consist of three parallel combinations of resistor (R) and capacitor (C) in series as three major peaks in DRT function indicates the presence of different relaxation processes with major contributions from core grains along with smaller contributions from grain boundary and interfaces. The room temperature frequency dependence of dielectric constant, loss tangent and ac conductivity is also studied for the CZTS films.     

Al3+ doping induced changes of structural,morphology, photoluminescence,optical and electrical properties of SnO2 thin films as alternative TCO for optoelectronic applications

Highly transparent and conductive pure (SnO₂) and aluminum doped tin oxide (Al:SnO₂) thin films were deposited on glass substrates by the sol-gel spin-coating method. The structural, morphological, optical and electrical properties of the prepared thin films at different doping rates have been studied. X-ray diffraction results revealed that all the films were polycrystalline in nature with a tetragonal rutile structure. SEM images of the analyzed films showed a homogeneous surface morphology, composed of nanocrystalline grains. The EDS results confirmed the presence of Sn and O elements in pure SnO₂ and Sn, O, Al in doped SnO₂ thin films. The optical results revealed a high transmittance greater than 85% in the visible and near infrared and a band gap varying between 3.82 and 3.89 eV. PL spectra at room temperature showed that the most dominant defects correspond to oxygen vacancies. A low resistivity of order varying between 10^?3 and 10^?4 Ω cm and a high figure of merits ranging between 10^?3 and 10^?2 Ω^?1 in the visible range were obtained. The best performances were obtained for samples containing 2 at. % Al, which could be used as an alternative TCO layer for future optoelectronic devices.     

Effects of ethyl acetate additive on Cu2ZnSnS4 solar cells fabricated with a facile dimethylformamide-based solution coating process

The solution based on dimethylformamide (DMF) has shown promising application prospects in the fabrication of high-efficiency Cu₂ZnSnS₄ solar cells. However, due to the high boiling temperature of the solvent, it is difficult to completely volatilize DMF during the evaporation process after spin coating, leading to remains of C and O atoms at grain boundaries, which severely restricts the photoelectric performance of solar cells. In this study, ethyl acetate (EA) with green character was used as an additive to optimize the film formation process of DMF-based CZTS precursor. The experimental results showed that using a small amount of EA additives could effectively improve morphology, crystallinity, composition distribution and electrical properties of the CZTS absorber. In addition, the CZTS and CdS heterojunctions exhibited a cliff-like energy band structure, and the optimized conduction band offset increased the activation energy required for the carrier recombination path, consequently reducing the carrier recombination. Compared with the pure DMF precursor solution, the photoelectric conversion efficiency of CZTS solar cells with an EA addition ratio of 10% was improved by 42%, and the open circuit voltage of the device reached 601 mV.     

Characterization of Cu(In,Ga)Se2 thin films prepared by RF magnetron sputtering using a single target without selenization

Cu(In_1?xGa_x)Se₂ (CIGS) thin films were prepared using a single quaternary target by RF magnetron sputtering. The effects of deposition parameters on the structural, compositional and electrical properties of the films were examined in order to develop the deposition process without post-deposition selenization. From X-ray diffraction analysis, as the substrate temperature and Ar pressure increased and RF power decreased, the crystallinity of the films improved. The scanning electron microscopy revealed that the grains became uniform and circular shape with columnar structure with increasing the substrate temperature and Ar pressure, and decreasing the RF power. The carrier concentration of CIGS films deposited at the substrate temperature of 500 °C was 2.1 × 10¹⁷ cm^?3 and the resistivity was 27 Ω cm. At the substrate temperature above 500 °C, In and Se contents in CIGS films decreased due to the evaporation and it led to the deterioration of crystallinity. It was confirmed that CIGS thin films deposited at optimal condition had similar atomic ratio to the target value even without post-deposition selenization process.     

Modifications in the structural,morphological, optical properties of Ag45Se40Te15 thin films by proton ion irradiation for optoelectronics and nonlinear applications

This current work reports the 30 keV proton ion irradiation induced structural, morphological, and optical properties change in Ag₄₅Se₄₀Te₁₅ films at different fluences. The thin films were irradiated with different ion fluences, such as 5 × 10¹⁵ ions/cm²,1 × 10¹⁶ ions/cm² and 5 × 10¹⁶ ions/cm². The electronic loss (S_e) dominates over the nuclear loss (S_n) in proton irradiation. The X-ray diffraction study shows the phase transformation from amorphous to crystalline upon ion irradiation. The Raman analysis confirms the change in chemical and vibrational bonds due to structural alterations in the films. The surface morphology has been studied by field emission scanning electron microscopy and the composition of the films has been checked by the energy dispersive X-ray analysis. The particle size increased upon the increase in ion irradiation fluence. The surface roughness of the films has been studied by atomic force microscopy. The transmission data is used to calculate the linear optical parameters. The absorption edge shifts towards the high wavelength region inferring the reduction in the optical bandgap. The linear refractive index of the films increased with ion fluence. The optical density increased at the high wavelength region while the skin depth decreased with fluence. The carrier concentration per effective mass decreased while the plasma frequency increased with proton irradiation. The nonlinearity (χ ⁽³⁾ and n₂) values increased significantly with the increase in fluences. Such kind of materials with optimization in their optical parameters are primarily essential for cutting-edge photonic, optoelectronic, and nonlinear optical applications.     

Synthesis of high-performance electrochromic thin films by a low-cost method

Metal-doping is an effective method to adjust the physical and chemical properties of semiconductor metal oxides. This work adopts a simple solvothermal method to synthesize Mo-doped tungsten oxide nanoparticles. The high-performance electrochromic films can be homogenously formed on ITO glass without post-annealing. Compared with pure WO₃ films, the optimized Mo-doped WO₃ films show improved electrochromic properties with significant optical contrast (68.3% at 633 nm), the short response time (6.3 s and 3.9 s for coloring and bleaching, respectively), and excellent coloration efficiency (107.2 cm² C^?1). The improved electrochromic behavior is mainly due to the increasing diffusion rate of Li⁺ in Mo-doped WO₃ films (increased 20% than that of pure WO₃ films). The porous surface of Mo-doped WO₃ film shortens the diffusion path of Li⁺. Besides, Mo doping reduces the resistance and improves conductivity. Furthermore, 2at% Mo-doped WO₃ films indicate satisfactory energy-storage properties (the specific capacitance is 73.8 F g^?1), resulting from the enhanced electrochemical activity and fast electrical conductivity. This work presents a practical and economical way of developing high-performance active materials for bifunctional electrochromic devices.     

Thermochromic properties of ZnO/VO2/ZnO films on soda lime silicate glass deposited by RF magnetron sputtering

A smart window based on VO₂ is a promising thermochromic (TC) glass that can regulate heat flow through windows by solar modulation near room temperature. TC glasses with high visible-light transmittance and large difference in infrared transmittance between high- and low-temperature VO₂ phases are required to save large amounts of energy in buildings. VO₂-based multilayer films with a buffer layer and/or an anti-reflective (AR) layer are used when the films are deposited by sputtering. In this study, VO₂-based multilayer films were prepared on soda lime glass using ZnO as both the buffer and the AR layers. The structure of the multilayer film was simulated using the optical constants measured from the deposited films. The effect of buffer and AR layers on the TC properties of VO₂-based multilayer films prepared by sputtering was investigated by simulation of the multilayer structure and deposition of the films with the simulated structure. The TC properties were measured and compared with the calculated properties. Improved TC properties (luminous transmittance (T_lum) of ～50%/46% (30 °C/80 °C) and solar modulation ability (ΔT_sol) of ～14%), compared to those without the buffer and AR layer, were obtained from the ZnO/VO₂/ZnO film deposited on glass. The calculated transmittances agree better with the measured ones when the optical constants measured directly from the deposited films are used and the roughnesses of the surface/interface of the multilayer films are considered in the calculation of the optical constants.     

Four-phases characterization of synthesised CeO2 thin films: Effect of molarity on structural,optical, physical properties and gamma-ray attenuation parameters

A group of novel CeO₂ thin films were synthesised using ultrasonic spray pyrolysis process. The composition ratios of these films were modified to investigate changes in their optical, surface, electrical, and structural characteristics. Absorbance spectra in the range 300–900 nm was acquired. Transmittance in the visible area was determined to be 50%. The optical band gap was reported to vary between 3.38 and 3.52eV using absorbance spectra. X-ray diffraction was used to analyse the films' structure, while atomic force microscopy was used to determine the surface roughness values. Spectroscopic ellipsometry and the Cauchy–Urbach model were used to calculate the thicknesses. Electrical resistivity values were determined using a four-probe system. CeO₂ thin film X-ray diffraction patterns validated the polycrystalline cubic fluorite structure. According to the data, the deposited films expand preferentially in the (2 0 0) direction. The films were found to have a high resistivity of 10⁶ Ω cm. We also evaluated the nuclear radiation shielding properties of CeO₂ thin films in the 0.015–15 MeV photon energy range. The results indicated that CeO₂ thin film exhibits promising half value layers of 0.00169 cm, 0.14055 cm, 1.62665 cm, and 2.30273 cm, respectively, for 0.015 MeV, 0.15 MeV, 1 MeV, and 15 MeV CeO₂ films have been determined to be worth working on and may be promising materials for optoelectronic and nuclear security applications.