Properties Of CdS Films Research Articles

An alternative chlorine-assisted optimization of CdS/Sb2Se3 solar cells: Towards understanding of chlorine incorporation mechanism

The current strategies in the development of Sb2Se3 thin film solar cells involve fabrication and optimization of superstrate and substrate device architectures, with the preferable choice for TiO2 and CdS heterojunction layers. For CdS-based superstrate cells, several studies reported the necessity to apply CdCl2 or other metal halide-based post-deposition treatment (PDT), highlighting improvement of CdS/Sb2Se3 device efficiency. However, the need, effect, and mechanism of such PDT are very often not described. Additionally, the fact that many groups have not succeeded in demonstrating its benefits suggests that this strategy is not straightforward, requiring a deeper understanding towards a more unified concept. The present study proposes an alternative approach to the challenging CdCl2 PDT of CdS in CdS/Sb2Se3 device, involving controllable Cl incorporation in CdS films by systematically varying the concentration of NH4Cl in the CBD precursor solution from 1 to 8 mM. Structural and electrical characterizations are correlated with advanced measurements of Scanning Kelvin Probe, surface photovoltage, and atomic force microscopy to understand the impact of Cl incorporation on the properties of CdS films and CdS/Sb2Se3 devices. The validity of Cl incorporation in the CdS lattice and interdiffusion processes at the CdS-Sb2Se3 interface is confirmed by secondary ion mass spectrometry analysis. It is demonstrated that incorporation of 1 mM of NH4Cl, as a Cl source in CBD CdS, can boost the PCE of CdS/Sb2Se3 by ∼20 %. With this approach, we offer new perspectives on the optimization methodology for Cl-based CdS/Sb2Se3 device processing and complementary understanding of the physiochemistry behind these processes.

Studying the effect of cadmium chloride and thiourea concentrations on the structural and optical properties of CdS films deposited using the spray pyrolysis technique

Studying the effect of cadmium chloride and thiourea concentrations on the structural and optical properties of CdS films deposited using the spray pyrolysis technique

Towards halide treatment on CdS thin films for solar cell applications: An evolution to ion size impact on segregation and grain boundaries passivation

In this study, an impact of halide ion size on the physical properties of 200 nm thin thermally evaporated CdS films is explored. The ex-situ halide treatment is performed using 0.2 M solutions of halide compounds viz. CdCl2, CdI2, MgF2, MgCl2 and MgI2 separately and subsequently air annealing at 200 °C. A detailed grain growth mechanism in CdS films based upon nature and size of cations and anions to the treatment species is deeply discussed. The recrystallization responsible for modulation in structural, optical, topographical, photoluminescence, electrical, morphological and compositional properties of CdS films is explored via formation of different complexes. The XRD patterns reveal formation of polycrystalline CdS thin films having mixture of cubic (with space group F4̅ 3 m) and hexagonal phases with (220) cubic preferential orientation. Different crystallographic constants are calculated and discussed where the crystallite size is varied from 34 nm to 48 nm with treatment. Surface topographical study indicates that surface roughness is altered with the halide treatment and observed maximum for MgCl2 treated CdS thin films. The pristine and halide treated CdS thin films show Ohmic nature owing to linear current-voltage behavior. Optical study demonstrates that MgI2 treated films have higher transmittance and lower absorbance and energy band gap is measured out in 2.04–2.48 eV range. PL spectra of CdS films reveal a strong red emission band appeared at ∼685 nm corresponding to Sulfur vacancies (VS) and possible A centers (XS+VCd2−)−. FESEM exploration reveals grain growth with probable activation where maximum grain size is obtained for MgF2 treated films. The EDS patterns confirm deposition of CdS films and also integration of F, Cl, I and Mg in the associated treated CdS films. The investigated findings reveal that size of halide ions plays a decisive role in modification of the physical properties of CdS thin films which could be implicated as optical window to CdTe and CIGS based photovoltaic devices.

Post deposition annealing effect on properties of CdS films and its impact on CdS/Sb2Se3 solar cells performance

Antimony selenide (Sb2Se3) is one of the emerging photovoltaic absorber materials possessing abundance and non-toxicity as the main attributes. Following CdTe technology, CdS is a widely used partner layer for Sb2Se3 solar cells. Related to CdS/Sb2Se3 device configuration, a number of studies reported findings and challenges regarding the intermixing phenomenon at the main interface and suitability of various annealing for CdS (and related interface) and still, significant room remains in developing strategies for interface optimization and understanding of the physiochemistry behind. In this perspective, this work provides a systematic investigation of the effect of vacuum and air annealing at temperatures between 200 and 400°C on the properties of CdS deposited by chemical bath deposition and combined with Sb2Se3 absorber obtained by close-spaced sublimation the direct impact of the CdS annealing on the device performance is illustrated. It is found that by varying the annealing temperature from 200 to 400°C in both, vacuum and air ambient, the morphology of CdS changes from highly dispersed small grain structure to sintered dense grains, the band gap decreases from 2.43 to 2.35 eV and the electron density drops from ∼1018 to ∼1011 cm−3. These changes were correlated with the changes in the CdS lattice and connected with the mobility of the OH group and the presence of secondary phases in CdS layers. 200°C air annealing of CdS was found as an optimal treatment resulting in 2.8% Sb2Se3/CdS cell efficiency - a 60% boost compared to the 1.8% performance of the device with as-deposited CdS. Material and device characterization analysis is performed, providing complementary insights on the interrelation between the physicochemical mechanism of the CdS annealing processes and device functionality.

High-efficiency Sb2Se3 thin-film solar cells based on Cd(S,O) buffer layers prepared via spin-coating

CdS films prepared via chemical bath deposition exhibit extremely good performance as a buffer layer of chalcogenide solar cells. However, their commercial application is very limited because of the production of a large amount of wastewater containing cadmium. In this study, we develop an efficient way to prepare CdS films using the spin-coating technique. The spin solution is anhydrous, and the oxygen content can be well controlled by changing the Cd/S content ratio in the solution. The crystal structure, morphology, and optical and electrical properties of CdS films with different Cd/S content ratios are characterized. The effect of the oxygen content on the device performance is investigated. We find that the introduction of an appropriate amount of oxygen can improve the carrier transport efficiency by decreasing the interface recombination. The spin-coated CdS films have good coverage of the substrate for film thicknesses below 50 nm. By the optimizing of Cd/S content ratio, we achieve an improved efficiency of 5.76% for the Sb2Se3 solar cells. This preparation technique is sufficiently simple for large-scale processing and produces much less wastewater containing cadmium; thus, it is promising for application to future large-scale solar cell production.

Properties of (Cd, Zn)S films deposited by DC co-sputtering

CdS thin film is commonly used as a buffer layer in most thin film solar cells. However, the buffer layer with less absorption in the visible region of the solar spectrum as well as that which provides perfect lattice matching with the absorbers is required. The incorporation of Zn in the CdS films can affect the structural and optical properties of the buffer layer. In this work, films of CdS and (Cd,Zn)S films were deposited by DC sputtering utilizing CdS and Zn targets. The concentration of Zn in the CdS was varied by changing the sputtering power of the Zn target. The influence of Zn concentration on the structural and optical properties of CdS films was investigated using X-ray diffraction (XRD) and Ultraviolet-Visible-Near Infrared (UV-VIS-NIR) spectroscopy, respectively. The XRD patterns confirm the growth preferential orientation of all films along the (002) plane. UV-VIS spectroscopy results indicate absorption edge shifts toward lower wavelength with an increase of Zn concentration in the CdS. The band gap evaluated by the Tauc plot of these films varied from 2.40 eV to 2.50 eV. The increased bandgap induces the density of localized states on the edge of the bandgap which leads to the increase in the Urbach tail width.

Effect of cadmium sources on the structural, morphological, and optical properties of CdS films for solar cell applications

The variations in the structural, morphological, and optical properties of three CdS films deposited with different cadmium ion sources namely cadmium acetate, cadmium chloride, and cadmium sulfate are reported in this article. All three CdS films possess cubic crystalline structure with the most prominent cubic phase (111). The CdS film deposited with cadmium acetate showed the best crystallinity among them. The presence of both Cd and S with a difference in the percentage of its existence depending upon the type of cadmium source chosen is obtained in the elemental analysis of the CdS films. CdS film deposited from acetate based chemical solution exhibited broad transmittance behaviour in the visible wavelength region due to its superior surface morphology. The energy band-gap values for CBD-CdS films deposited with cadmium acetate, cadmium chloride, and cadmium sulfate are found as 2.30eV, 2.23eV, and 2.32eV, respectively. The film deposited with cadmium acetate showed better IR response and more intense PL emission peaks as compared to the other two films. The efficiency of the CdTe/CdS cell fabricated with CdS window layer deposited with cadmium acetate is found to be 10.02%.

Role of Cu dilute on microstructures, optical, photoluminescence, magnetic and electrical properties of CdS film

Thin films of CdS1-xCux (with 0 ≤ x ≤ 0.10) were deposited using electron beam evaporation. Using XRD, EDX, SEM and UV–Vis–NIR spectroscopy, the impact of [Cu]/[S] on the film properties was examined. The influences of various concentrations of Cu are also elucidated on the optical parameters of the films. The XRD analysis shows that the thin films of CdS1-xCux have been improved and have hexagonal polycrystalline structure with the increase of Cu doping ratio. Additionally, the crystallite size is reduced while the micro-strain ε increases with enhancement of the incorporation of Cu in CdS lattice. The envelope method was used to extract the optical parameters of the undoped and Cu-doped CdS films. With the increase of Cu concentration, the energy optical bandgap decreased, and the variation values of band gap could play an important role in solar cell applications. Another optical parameters such as, dissipation factor and real/imaginary dielectric constant parts were evaluated and demonstrated a strong Cu doping dependence. The shift observed in the photoluminescence spectra emission band confirmed Cu's substitution to CdS lattice. The measurements of magnetization using vibrating sample magnetometer illustrated a hysteresis loop in Cu-doped CdS films, and confirmed the room temperature ferromagnetism. Finally, the Hall effect results show that the pure CdS film corresponds to an n-type semiconductor with a resistivity of 8.11 × 10-2 Ω cm and a carrier concentration of 29.6 × 1019 cm-3, and the CdS:Cu film is a p-type semiconductor and the resistivity is reduced from 6.8 × 10-2 to 3.7 × 10-2 Ωcm, and the carrier concentration is reduced from 26.4 × 1019 to 4.1 × 1019 cm-3, which has potential application prospects in solar cells.

Effect of the reactant concentration, bath temperature and deposition time on the properties of CdS thin film prepared by the chemical bath deposition method

CdS thin films for window layers in CdTe solar cells were deposited by the chemical bath deposition method without stirring. The influences of the deposition parameters were studied, such as the reactant concentration, deposition temperature and time on the film properties and solar cell performances, in order to apply in the fabricating of large-area solar cells. Here, we have considered the optical, morphological and structural properties of CdS films with the variation of deposition parameters by using UV–Vis spectroscopy, scanning electron microscopy and X-ray diffraction. Optical measurements revealed that maximum transmittance was obtained for S/Cd ratio of 6. It was found that film grown at 85 °C had better transmittance and showed more compact and smooth surface by means of UV–Vis and SEM measurements. We have demonstrated the transition of cubic and hexagonal crystal phases by the variation of solution PH with NH4Cl concentration through the XRD analysis. The performance of solar cells were estimated by measuring I–V characteristics with different S/Cd ratio, the open circuit voltage and fill factor at different deposition temperature and time. We have determined the optimal parameters such as reactant concentration of CdCl2: 1 mM, (NH2)2CS: 6 mM, NH4Cl: 20 mM, NH3H2O: 1 M, PH: 10.5, bath temperature: 85 °C, deposition time: 1 h.

Composition dependent structural, morphological, optical and electrical properties of CdS:Co window layer grown by chemical bath deposition

CdS as an n–type layer plays an important role in the fabrication of solar cells. Cd1-xCoxS thin-films with variable Co doping levels (x = 0 to 0.06) were deposited on glass and indium tin oxide-coated (ITO) glass substrates by simple and inexpensive chemical bath deposition. The effects of Co doping on the structural, optical, morphological, elemental, and vibrational properties of CdS films were systematically examined. XRD results revealed that Co concentrations increase and the crystallite size of the film decreases from 20.4 to 13.6 nm due to the incorporation Co in Cd sites. The optical bandgap was reduced from 2.44 to 2.32 eV due to the incorporation of Co, which was found with a UV–Vis spectrophotometer. Urbach energy, refractive index and extinction coefficient of all deposited films was estimated, and the results were discussed. The intensity of PL peaks was reduced by increasing the Co concentration in the red region. The resistivity and carrier concentration were measured from Hall measurement system and the film current density was increased from 7 to 26 mA/cm2 by cobalt doping.

Effect of the Dielectric Barrier Discharge Plasma on the Optical Properties of CDS Thin Film

Cadmium sulphide CdS films with 200 nm have been prepared by thermal evaporation technique on glass substrate at substrate room temperature under vacuum of 10-5mbar.In this paper, the effect of Dielectric Barrier Discharge plasma on the optical properties of the CdS film. The prepared films were exposed to different time intervals (0, 3, 5, 8) min. For every sample, the Absorption A, absorption coefficient α , energy gap Eg ,extinction coefficient K and dielectric constant ε were studied. It is found that the energy gap were decreased with exposure time, and absorption , Absorption coefficient, refractive index, extinction coefficient, dielectric constant increased with time of exposure to the plasma. Our study considers the first investigation of the effect of cold atmospheric plasma on the optical properties of CdS film.

Effect of the thiourea incorporation velocity and RTA post-deposit treatments, on the properties of CdS films deposited by CBD

In this work the influence of the thiourea incorporation velocity, or drip time (td), on the properties of the CdS films deposited by chemical bath deposition technique (CBD) was studied. The thiourea was employed as the sulfur source in the bath solution. The films were deposited on glass substrates keeping the bath solution temperature (Tb) at 90 °C and varying the td from 10 to 60 min. The other reagents used were cadmium acetate, ammonium acetate, ammonium hydroxide and deionized water as an aqueous medium, whose concentrations were constant. The dependence of the thickness with td showed three regions associated with three growth stages: i) induction period, ii) linear growth and iii) saturation stage. The best structural, optical and electrical properties were obtained in the linear growth region (20 min ≤ td ≤ 40 min). These films exhibited a crystallite size around 35 nm and a resistivity value of ∼100 Ω-cm. With respect to their optical properties, an average transmittance value of 70% for λ ≥ 500 nm and Eg of 2.35 eV were obtained. The presence of organic compounds was determined by FTIR spectra. The main organic compound identified was cyanamide, whose concentration was greater and constant at linear growth region. Afterwards, the effect of rapid thermal annealing (RTA) treatments on the properties of the CdS films, was evaluated for three films of the linear growth region. Such treatments did not modify the thickness, crystalline structure and crystallite size of the films. However, there was a change of color from light orange to dark orange, and a shift of Eg to 2.27 eV without the detriment of the transmittance. The CdS optical constants (n, k, ε) obtained from an optical model, confirmed the shift. In addition, photoluminescence spectra after RTA treatment showed a decrease of the defects associated to the radiative bands: green (2.21 eV), red (1.88 eV) and nanoparticles (2.94 eV), this without a change in the orange band (2.04 eV). The cyanamide, main organic compound present in the films, decreased significantly with thermal treatment, producing a resistivity drop from ∼100 to 4 Ω-cm. The drop of resistivity was attributed to the decrease of both, cyanamide and radiative defects concentration. The RTA treatments lead to CdS films with low resistivity and good transmittance, making them appropriate to be used as window material in solar cells.

Structural, optical, electrical and morphological properties of CdS films deposited by CBD varying the complexing agent concentration

Abstract CdS thin films were deposited on commercial glass substrates by CBD technique at constant temperature and deposition time of 90 °C and 50 min, respectively. The reaction was performed by mixing cadmium acetate, ammonium acetate, ammonium hydroxide, thiourea, and deionized water as an aqueous medium. The S/Cd ratio in the solution was kept constant at 4.46 to make sure that the films were as stoichiometric as possible. Optical, electrical, structural properties and the presence of organic compounds in the films were studied modifying the concentration of ammonium hydroxide (complexing agent) in the bath solution. X-ray diffraction patterns show that all films have the cubic phase with a preferential orientation in the plane (1 1 1). An increase of the film’s resistivity from 102 to 107 Ω-cm is observed by increasing the ammonium hydroxide concentration in the solution in the narrow interval of 0.18–0.36 M. Transmittance values up to 70% are obtained at the lowest concentrations of this reagent, obtaining from these spectra the highest value of the direct bandgap, 2.37 eV. Results about the presence of organic compounds and their influence on the photoluminescence properties are shown, which have not been reported to date. The main organic compound identified by FTIR is cyanamide, whose concentration is higher at the lowest ammonium hydroxide concentrations. Photoluminescence spectra of the films show green, red and orange bands, located at 2.27 eV, 1.78 eV, and 2.02 eV, respectively. An additional band was observed with low intensity at 2.99 eV associated with the presence of nanoparticles in some films. The films with the lower presence of defects, higher uniformity and best optical, electrical and structural properties for their use as window material in solar cells are those deposited from a bath solution with a 0.24 M concentration of the complexing agent.

Structural, vibrational, optical, morphological and compositional properties of CdS films prepared by a low-cost electrochemical technique

Very dense and uniform thin films of CdS were deposited on fluorine-doped tin oxide (FTO) substrates for thin film semiconductor devices application, such as in solar cells. The simplified electrochemical deposition method applied uses two-electrode system with FTO as the working electrode and high-purity graphite rod as the counter electrode. The CdS films grown at different cathodic voltages (1500 mV, 1550 mV and 1600 mV) were characterized for their structural, vibrational, optical, morphological and chemical compositional properties using state-of-the-art glancing incidence X-ray diffraction (GIXRD), Raman spectroscopy, UV–Visible spectrophotometry, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) respectively. XRD results reveal the existence of pure hexagonal crystal structure of CdS in the films in both as-grown and heat-treated conditions. The size of crystallites are in the range of (9–14) nm and (11–17) nm while the size of grains in these highly uniform and dense films are in the range (180–860) nm and (270–880) nm before and after annealing respectively. Raman results show the typical fingerprint of CdS in the form of the 1LO and 2LO phonon vibration peaks. The energy bandgaps obtained from optical measurements fall in the range of (2.50–2.59) eV which narrow down to 2.42 eV after annealing, for the different growth voltages used. EDX reveals all the films to be S-rich, with Cd/S ratio of ∼0.9 after annealing.

Importance of CdS buffer layer thickness on Cu2ZnSnS4-based solar cell efficiency

Cu2ZnSnS4 (CZTS) thin films were grown on Mo-coated soda lime glass (SLG) substrates by the sulfurization of DC magnetron-sputtered Zn, Sn and Cu metallic precursors under a sulfur atmosphere at 550 °C for 45 min. Understanding the composition and structure of the CZTS absorber layer is necessary to obtain efficient solar cells. With this aim, x-ray diffractometry, Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy and x-ray photoelectron spectroscopy were used to investigate the CZTS absorber layers. CZTS absorber films were obtained and found to be Cu-poor and Zn-rich in composition, which are both qualities desired for efficient solar cells. CdS was used as a buffer layer and was grown by the chemical bath deposition technique. The optical properties of CdS films on SLG were searched for using a spectroscopic ellipsometer and the results revealed that the bandgap increases with film thickness increment. CZTS-based solar cells with different CdS buffer layer thicknesses were prepared using a SLG/Mo/CZTS/CdS/ZnO/AZO solar cell configuration. The influence of the CdS buffer layer thickness on the performance of the CZTS solar cells was investigated. Device analysis showed that electrical characteristics of solar cells strongly depend on the buffer layer’s thickness. Highly pronounced changes in VOC, fill factor and JSC parameters, which are the main efficiency limiting factors, with changing buffer layer thicknesses were observed. Our experiments confirmed that decreasing the CdS thickness improved the efficiency of CZTS solar cells down to the lowest thickness limit.

Improving the structural and optical properties of CdS films grown by Chemical Bath Deposition with adding H2O2

For the first time, H2O2 was used in CdS thin films deposition by Chemical Bath Deposition method. With the oxidant, a more compact CdS films were fabricated. The average grain size decreases from 88 nm to 15 nm with the increasing concentration of H2O2 that was used in CdS deposition. The growth mechanism has been discussed in view of the reaction between H2O2 and Cd clathrate in solution. The fill factor of CdS/CdTe device deposited on oxygenated CdS film increases about 18%.

Growth process and properties of CdS thin films prepared by chemical bath deposition at different pH values

CdS thin films were successfully fabricated on glass substrates in different pH solutions by chemical bath deposition (CBD). The influences of pH value on the thickness, growth process, structure as well as on the optical properties of CdS film were investigated. The as-deposited films exhibited pure cubic phase structure, indicating that the pH had no significant effect on the crystal structure of CdS film. The optical transmittance spectra demonstrated that the films deposited at 11.7 and 11.8 pH exhibited relatively high transmittance in the long wavelength. And the optical band gaps decreased from 2.42 to 2.31 eV with increasing pH values. Subsequently, the growth process of CdS films was studied by analyzing the morphologies and particles sizes at different growing stages of the deposition. It was found that the particle clusters produced by homogeneous reaction acted as nucleation sites during the deposition process, and CdS preferred to grow on their surface. As a result, the sizes of clusters expanded with deposition time until a continuous film was formed, and the duration to obtain a continuous film reduced with decreasing pH values. Hence, a growth mode of CdS film on the glass substrate was proposed, i.e. the film was formed by the connection of expanded particle clusters produced by homogeneous reaction.

Effect of chelating reagents on nanostructured CdS layer morphology in CdS-sensitized TiO2 solar cells by successive ionic layer adsorption and reaction (SILAR) method

The chelating reagent is one of effecting factors which determines the properties of CdS films. Film morphology and roughness are very crucial in determining the further photovoltaic performance of the device. In this work, CdS film was synthesized by successive ionic layer adsorption and reaction (SILAR) method on FTO/TiO2 substrate. Different chelating reagents with N and S donating atoms were used in Cd2+ solution to investigate their effect on CdS film properties. X-ray diffraction spectroscopy (XRD), atomic force microscopy (AFM), ultraviolet-visible [1] spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy were used for characterization of the films. Quantum dot-sensitized solar cells (QDSCs) were fabricated by using different produced photoanodes and the photocurrent density–voltage curves of the assembled solar cells were measured. Computational quantum chemistry methods were used for calculation of binding energy, topological properties between chelating reagents and CdS film. The HOMO and LUMO molecular orbitals were calculated and visualized. Experimental and theoretical results confirmed that the ligand containing S donating atom results in formation of CdS film with the lowest surface roughness and the highest photovoltaic conversion efficiency compared to the other ligands.

Comparison of the Structural Electrical and Optical Properties of CdS Films Deposited by Chemical Bath Deposition and Spray Pyrolysis

Comparison of the Structural Electrical and Optical Properties of CdS Films Deposited by Chemical Bath Deposition and Spray Pyrolysis

Deposition of Nanostructured CdS Thin Films by Thermal Evaporation Method: Effect of Substrate Temperature.

Nanocrystalline CdS thin films were grown on glass substrates by a thermal evaporation method in a vacuum of about 2 × 10−5 Torr at substrate temperatures ranging between 25 °C and 250 °C. The physical properties of the layers were analyzed by transmittance spectra, XRD, SEM, and four-point probe measurements, and exhibited strong dependence on substrate temperature. The XRD patterns of the films indicated the presence of single-phase hexagonal CdS with (002) orientation. The structural parameters of CdS thin films (namely crystallite size, number of grains per unit area, dislocation density and the strain of the deposited films) were also calculated. The resistivity of the as-deposited films were found to vary in the range 3.11–2.2 × 104 Ω·cm, depending on the substrate temperature. The low resistivity with reasonable transmittance suggest that this is a reliable way to fine-tune the functional properties of CdS films according to the specific application.