CdS Deposition Research Articles

Formation of CdS Thin Film on Different Substrates Using Electrochemical Atomic Layer Deposition (E-ALD)

With solar energy being a promising alternative to fossil fuels, the need for high quality and high efficiency photovoltaic (PV) materials is obvious. As a major component in thin film solar cells, CdS thin film can be combined with absorber layers such as CdTe or CIGS (Cu, In, Ga, Se) to form p-n junction for light energy conversion.1 Electrochemical deposition is a low cost and controllable method for the fabrication of CdS thin films. Electrochemical atomic layer deposition (E-ALD) is the electrochemical form of atomic layer deposition that utilizes surface limited reaction to deposit one or less than one layer of element each time.2-3 High quality thin films can be using E-ALD but may take a relatively long time. Thus E-ALD is particularly suitable for making CdS films where a thickness as low as 50 nm is sufficient for the heterojunction formation.4 CdS thin films on Au have been made using E-ALD, and the film thickness increases linearly with increasing cycle number. The resulting CdS thin film is a single crystal with cubic <111> structure. SEM images show a conformal coating of CdS on Au substrate with a grain size of around 70 nm. The same method is applied to form CdS thin film on Ag and Ag nanorods for enhanced photoelectrochemical response. Preliminary study of CdS deposition on indium-tin-oxide (ITO) has been conducted by reducing the oxide substrate to a minimum amount of metallic surface to increase the nucleation sites for film growth.

Evolution of Cu2ZnSnS4 during Non-Equilibrium Annealing with Quasi-in Situ Monitoring of Sulfur Partial Pressure

Chalcogen-based materials like Cu2ZnSnS4 (CZTS) have attracted extensive attention for applications such as photovoltaics and water splitting. However, an inability to monitor the sulfur partial pressure (PS2) during the non-equilibrium annealing process at high temperatures complicates the synthesis of CZTS with controlled optoelectronic properties. Here we demonstrate that PS2 can be monitored by investigating the Sn–S phase transformation. We showed that PS2 drops considerably over the annealing time, causing gradual alterations in CZTS: (i) a change in defect type and (ii) evolution of ZnS and SnxSy phases. With additional ordering treatment, we observed that the low room-temperature photoluminescence energy usually seen in CZTS can result from insufficient PS2 during annealing. It is proven that remarkable Voc beyond 700 mV for solar cells with nonoptimal CdS buffer can be repeatedly achieved when CZTS is prepared under a sufficiently high PS2. An ordering treatment before CdS deposition can further ...

Fabrication and study of optical properties on CdS semiconductor as buffer layer for Cu(In,Ga)Se2 thin film solar cells

CdS nanostructures have been fabricated using cadmium acetate dihydrate and Cd(II)-Salophen as precursors via different chemical methods such as chemical bath deposition and electrodeposition. Electrochemical deposition experiments were performed by means of potentiostatic method. The effects of the precursor type, deposition time and method on the structural, morphological, chemical composition and optical properties of these films were investigated. The thin films are characterized by X-ray diffraction pattern, scanning electron microscopy, transmission electron microscopy, UV–Vis diffuse reflectance spectroscopy and energy dispersive X-ray analysis spectroscopy. Current density–voltage (J–V) curve was used to investigation of CIGS solar cells made by electrodeposition method. To the best our knowledge, this is the first report on the synthesis of CdS nanostructures by Cd(II)-Salophen as an inorganic precursor for application in CIGS solar cells. It was found that electrodeposition method is the best technique for deposition of CdS on the FTO surface for using in CIGS solar cell. The highest efficiency obtained for n-CdS/p-CIGS solar cells was 0.01% (FF = 27%) with a synthesized CdS layer using Cd(II)-Salophen as a new precursor.

Optical properties and photocatalytic activity of CdS-TiO2/graphite composite

AbstractTiO2film was applied to graphite substrate through chemical bath deposition (CBD) method with TiCl4as precursor. CdS was deposited on TiO2/graphite (TiO2/G) by CBD with precursors of CdSO4. A UV-Vis diffuse reflectance (UV-Vis DR) analysis was used to analyze the optical properties and band gap energy. Meanwhile, photocatalytic activity was determined from the quantum yield (QY) value of isopropanol degradation. The X-ray diffraction pattern shows that the TiO2film contains rutile and anatase phases. UV-Vis DR spectrum shows the photoactivity in the visible light area and provides lower band gap value due to CdS deposition. TiO2/G provide energy gap at 3.0 eV, which indicates that rutile phase is dominant. Meanwhile, CdS-TiO2/G shows multiple energy gaps representing CdS at 2.4 eV, rutile at 3.0 eV, and anatase at 3.2 eV. The QY values of CdS-TiO2/G are 7.98×10-3and 8.62×10-4at 450 and 380 nm of radiation light, respectively. These values are higher than the QY of TiO2/G and TiO2-P25/graphite (TiO2-P25/G), which are 1.19×10-4and 5.0×10-4, respectively. The photocatalytic reaction follows the first-order reaction. CdS deposition allows the rate constant to increase from 2×10-3to 13×10-3under UV radiation.

A space‐charge‐free CdS, and a new solar cell without pn‐junction enabled by high‐field domains

A review of the electrical properties of a copper doped CdS as a model semiconductor describing three independent thermodynamic states depending on optical excitation and bias. These are the traditional ground state that, dependent of optical excitation renders it from an insulator to a highly conductive n‐type semiconductor. With higher applied voltage, a high‐field domain occurs that is locked‐in, attached to the cathode. It presents the second thermodynamic stable state that is n‐type with constant drift current limited by the carrier density at a blocking electrode nc. With further increased bias, the high‐field domain becomes anode‐adjacent. The CdS is in its third thermodynamic stable state. Here, the CdS has flipped into p‐type conductivity with the current limited by the hole density at the blocking anode pa. In both states, the CdS is free of space charges within the domain that permits defect level spectroscopy without broadening influence of fluctuating electric fields. The minimum entropy production principle connects the work functions of blocking cathode and anode by the constant domain current, and permits the measurement of their values that depend on the optical excitation. A new solar cell is described that works without a pn‐junction, with a thin, pure CdS layer replacing the junction. The CdS extracts the holes for tunneling into the base electrode. The CdS/CdTe to scale model is given as an example. It has substantial increased efficiency by preventing junction leakage and permits an increase of the open circuit voltage to approach the theoretical limit of the band gap of the emitter when extrapolated to 0 K. The solar cell is series resistance limited by the CdS and requires a thin planar deposition of CdS. Since CdS is photoelectrically passive, its Fermi‐level at the base electrode is fixed. A Gallium doping of a thin layer pins the Fermi level within 0.05 V to the conduction band and increases Voc further. All properties of CdS with high‐field domains are described quantitatively and the domains are made visible by the Franz–Keldysh effect.

Сomposite Powders TiO&lt;sub&gt;x&lt;/sub&gt;/CdS Synthesis and the Study of their Optical and Photocatalytic Properties

TiOx/CdS composites were synthesized by CdS deposition on TiOx from aqueous solutions of Cd (CH3COO)2 and Na2S with and without addition of a stabilizing agent–Na2SiO3. Initial high-defective TiOx nanocrystalline powders were prepared by pulsed laser ablation (Nd:YAG laser, 1064 nm, 7 ns) of Ti target in H2O. Composites obtained exhibit absorption in the visible range up to 520 nm. On the example of Rhodamine C photodecomposition in water it was revealed that the nanocomposite TiOx/CdS powders obtained exhibit good photocatalytic properties when excited by visible light.

Effect of CdS deposition temperature for thermally grown Cu(In,Ga)Se2 and two-step chalcogenized Cu(In,Ga)(S,Se)2 absorbers on solar cell performances

CdS buffer layer of varying thickness ranging from 23 to 58 nm deposited at different substrate temperature were prepared as n-type junction partner for thermally grown Cu(In,Ga)Se2 and two-step chalcogenized Cu(In,Ga)(S,Se)2 photovoltaic absorber films and the effect of deposition temperature and time on the CdS growth behavior and solar cell performance were evaluated. High deposition temperature resulted in a thicker CdS layer and more importantly lower density and shallower depth of open voids, which attributed to the improved open-circuit voltage and fill factor due to reduced interface recombination. The solar cell efficiency of thermally grown absorber saturated at about 30 nm thickness of CdS, while that of chalcogenized absorber gradually increased with CdS thickness up to 60 nm without significant loss of short-circuit current density.

Cu2ZnSnS4 photovoltaic cell with improved efficiency fabricated by high‐temperature annealing after CdS buffer‐layer deposition

AbstractTo improve the photovoltaic properties of Cu2ZnSnS4 (CZTS) cells, we investigated the effect of both the thickness of the deposited CdS layers and the post‐annealing temperature following CdS deposition on the photovoltaic properties of CZTS cells using a two‐layer CZTS structure. By depositing a thin CdS layer (40 nm) followed by high temperature annealing (603 K), we observed a remarkable increase in the short‐circuit current density because of the enhancement of the external quantum efficiency in the wavelength range of 400–800 nm. The best CZTS cell exhibited a conversion efficiency of 9.4% in the active area (9.1% in the designated area). In addition, we also fabricated a CZTS cell with open‐circuit voltage of 0.80 V by appropriately tuning the composition of the CZTS layers. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Boosting the power conversion efficiency of quantum dot sensitized solar cells via g-C3N4 modified TiO2 nanoparticles

In spite of the great development in quantum dot sensitized solar cells (QDSSCs), enrichment of material system of QDSSCs is still imperial mission for further advances. In this report, two-dimensional graphitic carbon nitride (g-C3N4) prepared from urea was applied to modify porous TiO2 photoanodes, followed by the deposition of CdS and CdSe QDs as sensitizers. In the as-prepared photoanodes, g-C3N4 functioned as barrier for retarding electron backward recombination and assisted to strengthen light absorption. Compared with the pure TiO2 photoanode, the photoelectrical behaviors of g-C3N4 modified TiO2 photoanode were obviously improved. By optimizing the loading amount of g-C3N4, the champion performance was achieved at 15% addition amount of g-C3N4 with shortcircuit current density of 15.1 mA cm−2, open circuit voltage of 0.56 V, and energy conversion efficiency of 4.14% under AM 1.5 illumination. The improvement in cell performance was attributed to the type II alignment between g-C3N4 and TiO2, which induced the fast separation of photogenerated carriers. The transfer of the photogenerated electrons and holes is driven by the conduction band offset of 0.39 eV and the valence band offset of 0.86 eV, respectively. Present results provided a new insight for further optimum photoanode structures of QDSSCs.

What is the dopant concentration in polycrystalline thin-film Cu(In,Ga)Se2?

We compare the dopant concentration of polycrystalline Cu(In,Ga)Se2 thin film absorbers derived from Hall and capacitance-voltage measurements. Although both measurements techniques appear to be reliable, dopant concentrations determined by capacitance-voltage analysis are significantly lower and vary with probing depth into the absorber. The doping profiles and differences between both measurement techniques are consistent with Cd in-diffusion from the CdS buffer layer during solar cell fabrication. Different doping profiles obtained after a variation of the CdS deposition process support this scenario.

Method for a High-Rate Solution Deposition of Zn(O,S) Buffer Layer for High-Efficiency Cu(In,Ga)Se2-Based Solar Cells

We present a method for high-rate solution growth of the Zn(O,S) buffer layer to achieve deposition rates and material consumptions far below the standard Zn(O,S) and CdS deposition method. We replace the organosulfide thiourea by the more quickly decomposable thioacetamide and control the reaction kinetics by the use of chelating ligands and ammonia. We characterize the produced layers by secondary neutral mass spectrometry, X-ray diffraction, and optical transmission. For cell preparation, we use high-efficiency Cu(In,Ga)Se2 with an alkali-modified surface, as well as industrially relevant inline absorber material. We realize a certified 21% cell efficiency with the standard thiourea-based Zn(O,S) and first cells with over 19 % with the high-rate Zn(O,S) buffer.

Effect of ultrasonically generated water vapor treatment on the Cu2ZnSnS4/CdS heterojunction-based photovoltaic cells

The surface treatment of Cu2ZnSnS4 thin films was carried out by utilizing ultrasonically generated water vapor. Suppression of the unintentional fluctuation of chemical composition near the heterointerface and enhancement in the homogeneity of CdS deposition on the Cu2ZnSnS4 thin films were observed in the samples with water vapor treatment at the temperatures between 250°C and 350°C. The effect on the variation of conduction band and valence band offsets at the Cu2ZnSnS4/CdS heterojunction, which was observed to be in a staggered alignment, was less than ±50meV due to the treatment. Reproducibility of the cell characteristics was improved by the H2O spray treatment of the Cu2ZnSnS4 absorbers before the deposition of CdS buffer layers. At treatment temperature of 300°C, the improvement of efficiency by about 25% compared to that of the untreated samples was achieved.

Effect of sodium acetate additive in successive ionic layer adsorption and reaction on the performance of CdS quantum-dot-sensitized solar cells

Abstract Sodium acetate (NaAc) is utilized as an additive in cationic precursors of the successive ionic layer adsorption and reaction (SILAR) process to fabricate CdS quantum-dot (QD)-sensitized photoelectrodes. The effects of the NaAc concentration on the deposition rate and distribution of QDs in mesoporous TiO 2 films, as well as on the performance of CdS-sensitized solar cells are studied. The experimental results show that the presence of NaAc can significantly accelerate the deposition of CdS, improve the QD distribution across photoelectrodes, and thereby, increase the performance of solar cells. These results are mainly attributed to the pH-elevation effect of NaAc to the cationic precursors which increases the electrostatic interaction of the TiO 2 film to cadmium ions. The light-to-energy conversion efficiency of the CdS-sensitized solar cell increases with increasing concentration of the NaAc and approaches a maximum value (3.11%) at 0.05 M NaAc. Additionally, an ionic exchange is carried out on the photoelectrode to transform the deposited CdS into CdS 1−x Se x ternary QDs. The light-absorption range of the photoelectrode is extended and an exceptional power conversion efficiency of 4.51% is achieved due to this treatment.

Highly Repeatable and Recoverable Phototransistors Based on Multifunctional Channels of Photoactive CdS, Fast Charge Transporting ZnO, and Chemically Durable Al2O3 Layers.

Highly repeatable and recoverable phototransistors were explored using a "multifunctional channels" structure with multistacked chalcogenide and oxide semiconductors. These devices were made of (i) photoactive CdS (with a visible band gap), (ii) fast charge transporting ZnO (with a high field-effect mobility), and (iii) a protection layer of Al2O3 (with high chemical durability). The CdS TFT without the Al2O3 protection layer did not show a transfer curve due to the chemical damage that occurred on the ZnO layer during the chemical bath deposition (CBD) process used for CdS deposition. Alternatively, compared to CdS phototransistors with long recovery time and high hysteresis (ΔVth = 19.5 V), our "multi-functional channels" phototransistors showed an extremely low hysteresis loop (ΔVth = 0.5V) and superior photosensitivity with repeatable high photoresponsivity (52.9 A/W at 400 nm). These improvements are likely caused by the physical isolation of the sensing region and charge transport region by the insertion of the ultrathin Al2O3 layer. This approach successfully addresses some of the existing problems in CdS phototransistors, such as the high gate-interface trap site density and high absorption of molecular oxygen, which originate from the polycrystalline CdS.

CdS sensitized TiO2 nanorod arrays based solar cells prepared with polymer-assisted layer-by-layer adsorption and reaction method

High performance CdS sensitized TiO2 nanorod arrays based solar cells are fabricated by polymer-assisted layer-by-layer adsorption and reaction (PA-LBLAR) method. The PA-LBLAR method can well control the deposited size of CdS on the TiO2 nanorod arrays, which are grown on Ti foils by hydrothermal route then transferred to transparent conductive glasses. The UV–vis absorption spectra show that with the increasing deposition times, the absorption spectra of photoelectrodes increased to a broader wavelength range, which is originated by the better coverage and increased size of CdS quantum dots on the TiO2 nanorod arrays as detected by SEM and TEM images. The highest power conversion efficiency of the cells (AM 1.5G, 100mWcm−2) up to 2.944% can be obtained with 7 cycles of PA-LBLAR deposition of CdS sensitized layers in the photoelectrodes, which is much higher than that of the best performance of cell with 14 cycles of traditional successive ionic layer adsorption and reaction processes.

Effect of Reaction Temperature of CdS Buffer Layers by Chemical Bath Deposition Method.

This study investigated CdS deposition on a Cu(In,Ga)Se2 (CIGS) film via chemical bath deposition (CBD) in order to obtain a high-quality optimized buffer layer. The thickness and reaction temperature (from 50 degrees C to 65 degrees C) were investigated, and we found that an increase in the reaction temperature during CBD, resulted in a thicker CdS layer. We obtained a thin film with a thickness of 50 nm at a reaction temperature of 60 degrees C, which also exhibited the highest photoelectric conversion efficiency for use in solar cells. Room temperature time-resolved photoluminescence (TR-PL) measurements were performed on the Cu(In,Ga)Se2 (CIGS) thin film and CdS/CIGS samples to determine the recombination process of the photo-generated minority carrier. The device performance was found to be dependent on the thickness of the CdS layer. As the thickness of the CdS increases, the fill factor and the series resistance increased to 61.66% and decreased to 8.35 Ω, respectively. The best condition was observed at a reaction temperature of 60 degrees C, and its conversion efficiency was 12.20%.

Hydrothermal deposition of CdS on vertically aligned ZnO nanorods for photoelectrochemical solar cell application

CdS/ZnO nanorods composite nanofilms were successfully synthesized via hydrothermal method on indium doped tin oxide glass substrates. Sequentially deposited CdS formed cauliflower like nanostructures on vertically aligned ZnO nanorods. The morphological, compositional, structural and optical properties of the films were characterized by field emission scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction and ultraviolet–visible spectroscopy. Photoelectrochemical conversion efficiencies were evaluated by photocurrent measurements in a mixture of Na2S and Na2SO3 akaline aqueous solution. The amount of deposit, as well as the diameter and crystallinity of the CdS cauliflower were found to increase with growth time. CdS/ZnO nanorods composite exhibited greater photocurrent response than ZnO nanorod arrays. Besides, the composite film with 90 min of growth duration displayed the highest photocurrent density which is nearly four times greater than plain ZnO nanorods under the illumination of halogen light. The result exhibited remarkable photoconversion efficiency (η) of 1.92 %.

Optimization of CBD-CdS physical properties for solar cell applications considering a MIS structure

While the standard interpretation treats CdS/CdTe, CdS/Cu(In,Ga)Se2(CIGSe) and CdS/kesterites as p-n junctions, some recent reports suggest these solar cells operate rather as a Metal-Insulator-Semiconductor (MIS) structure. In this paper, we report results about the dependence of electrical, optical, morphological and structural properties of CBD-CdS on growth conditions in order to obtain the best layers to be used in solar cells according to the MIS model. In particular, CBD-CdS thin films were synthesized by changing the complexing agents in the bath solution, the Cd source and the nominal S/Cd ratio. In order to study the impact of the different CdS deposition approaches, CIGSe and CZTSe solar cells were processed. The influence of CdS:Cu as well as Cd sources such as Cd(NO3)2 and CdSO4 on solar cell electrical parameters is studied.

Optimization of CdSe layer on modified ZnO hierarchical spheres by spin-SILAR for efficient CdS/CdSe co-sensitized solar cells

In this study, after CdS quantum dots sensitized ZnO hierarchical spheres (ZnO HS), we used a simple process to deposit CdSe QDs on ZnO by spin-coating-based SILAR, and applied to photoanodes of quantum dots-sensitized solar cells. Before CdS and CdSe QDs deposition, the ZnO HS photoanodes were modified by Zn(CH3COO)2·2H2O methanol solution to further enhance the open-circuit voltage and power conversion efficiency (PCE). The program of modifying photoanodes and the number of CdSe spin-SILAR cycles are evaluated on the optical and electrochemical properties of the cells. As a result, a high energy conversion efficiency of 2.49 % was obtained by using modified ZnO HS/CdS photoanode under AM 1.5 illumination of 100 mW cm−2. And further decorated by the CdSe QDs, the ZnO HS/CdS/CdSe cell achieved a PCE of 5.36 % due to the modification of ZnO HS nanostructure, the enhanced absorption in the visible region, the lower recombination reaction and higher electron lifetime.

Mo2C as Non‐Noble Metal Co‐Catalyst in Mo2C/CdS Composite for Enhanced Photocatalytic H2Evolution under Visible Light Irradiation

Co-catalysts are a major factor to enhance photocatalytic H2 activity; they are mainly composed of expensive noble metals. Here, we reported a new non-noble-metal co-catalyst Mo2 C that efficiently improves the photocatalytic H2 evolution of CdS under visible light irradiation. Mo2 C is prepared by temperature-programmed reaction with molybdenum oxide as precursor, and the Mo2 C/CdS composite is prepared by deposition of CdS on Mo2 C. The optimum composite 2.0 % Mo2 C/CdS shows a high H2 evolution rate of 161 μmol h(-1) , which is ten times higher than that of CdS alone and 2.3 times higher than the optimum for 1.0 % Pt/CdS. Moreover, the Mo2 C/CdS is stable for 50 h. This study presents a new low-cost non-noble-metal co-catalyst as a photocatalyst to achieve highly efficient H2 evolution.