One-step synthesis of CdS sensitized TiO₂ photoanodes for quantum dot-sensitized solar cells by microwave assisted chemical bath deposition method

Sensitized-type solar cells based on TiO? photoanodes and CdS quantum dots (QDs) as sensitizers have been studied. CdS QDs are grown on TiO? films, utilizing one-step microwave assisted chemical bath deposition (MACBD) method. This method allows a facile and rapid deposition and integration between CdS QDs and TiO? films. The photovoltaic performances of the cells fabricated using CdS precursor solutions with different concentrations are investigated. The results show that the cell based on MACBD deposited TiO?/CdS electrode achieves a maximum short circuit current density of 7.20 mAcm?2 and power conversion efficiency of 1.18 % at one sun (AM 1.5G, 100 mW cm?2), which is comparable to the ones prepared using conventional techniques.     

Dual impurity doping of buffer solution grown cadmium sulphide thin films: electrical and optical properties

The effects of incorporation of aluminum and chlorine simultaneously into buffer solution grown cadmium sulphide thin films (i.e. dual impurity doping), on the electrical and optical properties of the films for various concentrations of aluminum and chlorine in the range 0.0002–0.01 wt % have been investigated. The results showed that the thicknesses (and optical absorption) of aluminum doped CdS films increased slightly as the aluminum concentration was increased, leading to decrease in optical transmittance and bandgap energy, and improvement of the dark electrical conductivity of the films. For aluminum concentrations of 0.01 wt % and above, the electrical conductivity of the doped CdS films was impaired. The dark electrical conductivity of aluminum-doped CdS films is at least ten times that of pure Cds film and at least one hundred times in the presence of chlorine. Generally, in the presence of chlorine, the electrical conductivity and the optical transmittance of the aluminum-doped CdS films were improved to some extent for aluminum concentrations ≤0.001 wt %. Optical bandgap varies from 2.45 eV for pure CdS film to 2.30–2.35 eV for doped films. The possible mechanisms for these observed effects are discussed. © 2000 Kluwer Academic Publishers     

Effect of Bi3+ doping on the properties of chemically deposited GdS films

CdS films were prepared by a chemical bath deposition technique with different Bi concentrations (0.01 to 5 wt %) on glass substrates. Optical and electrical properties were studied with these films. It was observed that the absorption coefficient of the CdS film increases with Bi-doping up to 2 wt % and then decreases. These results are explained in terms of the crystallanity of the film. The optical band gaps (E_g) were determined and found to decrease with Bi-doping. The conductivity and thermoelectric power are higher for doped films than undoped CdS films. These results are explained by considering the existance of Cd²⁺ ions as donor centres in Bi-doped CdS films.     

磁控溅射法制备的CdS:Al薄膜的性质研究

采用Al和CdS双靶共溅射的方法, 调控Al和CdS源的沉积速率, 制备出不同Al掺杂浓度的CdS:Al薄膜。通过XRD、SEM、AFM、紫外-可见透射光谱分析、常温霍尔测试对CdS: Al薄膜的结构、形貌、光学和电学性质进行表征。XRD结果表明, 不同Al掺杂浓度的CdS:Al薄膜均为六方纤锌矿结构的多晶薄膜, 并且在(002)方向择优生长。SEM和AFM结果表明, CdS:Al薄膜的表面均匀致密, 表面粗糙度随着Al掺杂浓度的增加略有增加。紫外-可见透射光谱分析表明, CdS:Al薄膜禁带宽度在2.42~2.46 eV 之间, 随着Al掺杂浓度的增加而略微减小。常温霍尔测试结果证明, 掺Al对CdS薄膜的电学性质影响显著, 掺Al原子浓度3.8%以上的CdS薄膜, 载流子浓度增加了3个数量级, 电阻率下降了3个数量级。掺Al后的CdS薄膜n型更强, 有利于与CdTe形成更强的内建场, 从而提高太阳电池效率。用溅射方法制备的CdS:Al薄膜的性质适合用作CdTe薄膜太阳电池的窗口层。     

Annealing effects on the chemical deposited CdS films and the electrical properties of CdS/CdTe solar cells

CdS layers grown by chemical bath deposition (CBD) are annealed in the oxygen and argon-hydrogen atmosphere respectively. It has been found that the open circuit voltage of the CdS/CdTe solar cell increases when the CBD CdS is annealed with oxygen before the deposition of CdTe by close spaced sublimation (CSS), while the performance of the solar cell decreases when the CBD CdS is annealed with argon-hydrogen. Electronic properties of the CdS films are investigated using X-ray photo-electron spectroscopy (XPS), which indicates that the Fermi level is shifting closer to the conduction band after annealing in the oxygen and consequently a higher open circuit voltage of the solar cell can be obtained.     

Effects of junction formation conditions on the photovoltaic properties of sintered CdS/CdTe solar cells

Microstructures and properties of sintered CdS films on glass substrates and sintered CdTe films on polycrystal CdS substrates have been investigated. The CdS films, which contained 9 wt % CdCl₂ as a sintering aid and were sintered at 650° C for 1 h in nitrogen, are transparent and have an average grain size of 15m and an electrical resistivity of 0.5cm. The CdTe films, which were coated on the sintered CdS substrate and were sintered above 610° C for 1 h in nitrogen, have a dense structure with an average grain size larger than 5m. All polycrystal CdS/CdTe solar cells were fabricated by this successive coating and sintering method. The sintering temperature of CdTe films on the sintered CdS films was varied from 585 to 700° C. Compositional interfaces and p-n juctions are formed during sintering. The highest solar efficiency (7.18%) was found in a solar cell made by sintering the composite layer of glass-CdS-CdTe at 625° C for 1 h. A fabrication temperature below 610° C resulted in poor solar cell efficiencies due to the porous structure of the CdTe films and above 650° C also resulted in poor efficiencies due to the formation of a CdS_1-x Te_x layer at the interface and a large p-n junction depth.     

Physical properties of Bi doped CdTe thin films grown by CSVT and their influence on the CdS/CdTe solar cells PV-properties

The physical properties of Bi doped CdTe films, grown on glass substrates by the Closed Space Transport Vapour (CSVT) method, from different Bi doped CdTe powders are presented. The CdTe:Bi films were characterized using Photoluminescence, Hall effect, X-Ray diffraction, SEM and Photoconductivity measurements. Moreover, CdS/CdTe:Bi solar cells were made and their characteristics like short circuit current density (J_sc), open circuit voltage (V_OC), fill factor (FF) and efficiency (η) were determined. These devices were fabricated from Bi doped CdTe layers deposited on CdS with the same growth conditions than those used for the single CdTe:Bi layers. A correlation between the CdS/CdTe:Bi solar cell characteristics and the physical properties of the Bi doped CdTe thin films are presented and discussed.     

Quantum confinement effect of CdS nanoparticles dispersed within PVP/PVA nanocomposites

Nanocomposite films of CdS nanoparticles within PVP/PVA blend were prepared. The prepared films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, Ultraviolet–visible spectroscopy (UV–vis), transmission electron microscopy (TEM) and photoluminescence (PL) spectra. The amount of Cd⁺ used strongly influenced the size of the CdS nanoparticles, which was confirmed by XRD, UV–vis absorption spectra, PL emission spectra and TEM images. Smaller sized CdS nanoparticles were formed in higher content of cadmium. The results of XRD indicate that CdS nanoparticles were formed with hexagonal phase in the polymeric matrix. PL and UV–vis spectra reveal that nanocomposite films shows quantum confinement effect. Optical band gap and particle size were calculated and is in agreement with the results obtained from TEM data. The direct energy band gap was increased up to 2.86 eV.     

Electrochemical bath deposition technique: Deposition of CdS thin films

Cadmium sulphide thin films have been deposited onto chromium plated stainless steel substrates under the influence of electric field. The various deposition parameters such as speed of rotation of the substrates, temperature of the chemical bath, molar concentrations of solution and the strength of the electric field were kept at optimized conditions. The electrochemical photovoltaic (ecpv) cells are formed with CdS film electrodes. The properties of CdS films andecpv cells are monitored with selective values of the electric field employed in the controlled precipitation technique. This relatively new technique is described and the possible film formation mechanism suggested.     

Preparation and characterization of Chitosan/Konjac glucomannan/CdS nanocomposite film with low infrared emissivity

Novel organic-inorganic nanocomposite films were prepared with Chitosan (CS), Konjac glucomannan (KGM) and CdS by one-step synthesis. As-prepared films were characterized by IR spectra, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and infrared emissometer (IR). The results indicated that grown CdS dendrites were formed with reaction time of 12 h for Cd²⁺ and CS/KGM, and were well dispersed in CS/KGM with an average diameter of 40 nm. The CS/KGM/CdS nanocomposite films had significantly low infrared emissivity. When the mole ratio of CdS to summation of CS&KGM construction units was 1.0 with CdS size of 10-20 nm, the film got the lowest infrared emissivity value of 0.011, which could be attributed to the strong synergism effect existing between CS/KGM and CdS dendrites.     

电子束蒸发制备CdS多晶薄膜及性质研究

采用电子束蒸发工艺在普通玻璃衬底上制备了硫化镉(CdS)多晶薄膜,研究了不同衬底温度对薄膜结构、表面形貌及光透过率的影响.测试结果显示:(1)不同衬底温度下沉积的CdS薄膜均呈现了〈002〉晶向的高度优势生长,属于六方相结构.随着衬底温度的升高,还逐渐出现了〈103〉、〈004〉、〈105〉等六方晶向;(2)CdS多晶薄膜表面连续,致密性好,且晶粒大小随着衬底温度的升高而增大;(3)低温下制备CdS薄膜吸收谱有较宽的吸收边,随着衬底温度的升高,吸收曲线趋于陡直.制备样品在550nm波段后的平均透过率都超过70%,符合作为CdTe太阳电池的窗口层.     

Optical study on II-VI semiconductor nanoparticles in Langmuir-Blodgett films

Cadmium sulfide (CdS) nanoparticles formed within Langmuir-Blodgett (LB) films of stearic acid and calix[8]arene were studied with different optical methods including surface plasmon resonance (SPR), ellipsometry and UV-visible absorption and fluorescence spectroscopies. For the first time, the process of formation of CdS nanoparticles within LB films was monitored in-situ with SPR. The results of ellipsometry, SPR and UV-vis absorption spectroscopy were analyzed to evaluate simultaneously the thickness, refractive index and extinction coefficient of LB films. It was shown that all three parameters increase as a result of formation of CdS nanoparticles. Photoluminescence measurements provided direct confirmation directly for previous observation with UV-vis absorption spectroscopy of the blue spectral shift caused by CdS particles formation. The observed large Stoke's shift of the luminescence band is discussed in terms of the formation of "dark excitons" in the platelet-type CdS nanoclusters. AFM study shows the formation of pseudo-two dimensional platelets of CdS with the lateral dimensions in the range of 20-30 nm.     

Variations of interlayer structure in Cu x S/CdS bilayer thin film with annealing of CdS: an ellipsometric study

Irregularities at the interface in Cu _x S/CdS thin films can be controlled by annealing CdS film prior to chemiplating. The interlayer formed on CdS films annealed at 200°C is comparatively smooth. In CdS films annealed at higher temperatures, the interlayer is rather thick and the CdS intrusions into this layer are thin. An ellipsometric technique is used for this study and the effective medium theory which is utilized to interpret the results is based on the difference in reaction rate in the grains as well as grain boundaries during chemiplating.     

Interfacial reactions between thin metal films and polar {0001} oriented CdS substrates

The interaction between deposited Al films on opposite polar {0001} surfaces of CdS single crystals was investigated by Auger electron spectroscopy. Aluminium reacts strongly with CdS resulting in a chemical shift of the Al Auger peaks. A chemical drawing effect is believed to dominate with thinner films, while a chemical trapping effect is dominant with thicker films. A sharp boundary between Al and CdS was formed initially; however, due to the reactive out-diffusion, the boundary became extended (over tens of nanometres) with time. A possible mechanism is proposed to explain these observations. The behaviour of the two polar surfaces of CdS was virtually the same.     

CdS quantum dot sensitized nanocrystalline Gd-doped TiO2 thin films for photoelectrochemical solar cells

CdS quantum dot sensitized Gd-doped TiO₂ nanocrystalline thin films have been prepared by chemical method. X-ray diffraction analysis reveals that TiO₂ and Gd-doped TiO₂ nanocrystalline thin films are of anatase phase. The absorption spectra revealed that the absorption edge of CdS quantum dot sensitized Gd-doped TiO₂ thin films shifted towards longer wavelength side (red shift) when compared to that of CdS quantum dot sensitized TiO₂ films. CdS quantum dots with a size of 5 nm have been deposited onto Gd-doped TiO₂ film surface by successive ionic layer adsorption and reaction method and the assembly of CdS quantum dot with Gd-doped TiO₂ has been used as photo-electrode in quantum dot sensitized solar cells. CdS quantum dot sensitized Gd-doped TiO₂ based solar cell exhibited a power conversion efficiency of 1.18 %, which is higher than that of CdS quantum dot sensitized TiO₂ (0.91 %).     

CdS annealing treatments in various atmospheres and effects on performances of CdTe/CdS solar cells

In this work, a systematic research on CdS annealing treatments under various atmospheres had been done to understand their effects on CdS/CdTe solar cells. CdS films were prepared by a standard CBD method and annealed under various atmospheres, including Ar, Ar+H₂, O₂, Ar+S and Ar+CdCl₂. Morphological, structural, optical and chemical properties were investigated using Atom force microscope (AFM), X-ray diffraction (XRD), UV–VIS spectroscopy and X-ray photoelectron spectroscopy (XPS). Annealing treatments enhanced modifications of morphology, structure and electrical properties of CdS films. AFM showed different surface morphologies and roughnesses of CdS films annealed under various atmospheres. XRD indicated the transition of CdS films from metastable cubic structure to stable hexagonal structure after annealing treatment, especially annealed in Ar+CdCl₂. From XPS analysis, Fermi levels of CdS films shifted closer to conduction band after annealing under O₂ and Ar+CdCl₂, while the levels shifted away from conduction band under Ar+H₂ and Ar+S. The relationships between those modifications by annealing treatments and effects on the performance of solar cells were discussed. Solar cell based on CdS annealed with Ar+CdCl₂ had the best performance due to the high n-doping of CdS layer introduced by annealing process.     

Cadmium sulfide nanotubes thin films: Characterization and photoelectrochemical behavior

Monodisperse cadmium sulfide nanotubes (CdS NTs) with a diameter of 100 nm were synthesized on indium-doped tin oxide glass substrates using chemical bath deposition and self-sacrificial template technique. This CdS thin film was characterized by transmission electron microscope, scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy and UV-vis spectrophotometer. This film gave a short circuit photocurrent of 4.4 mA/cm², an open circuit photovoltage of 0.75 V, a fill factor of 0.49, and an overall conversion efficiency of 1.29% under a simulated solar illumination of 100 mW/cm². All these photoelectrochemical properties of the films were dependent on the microstructure of the nanotubes and the thickness of the film. A facile and efficient way to prepare CdS-based photoelectrodes for photoelectrochemical cells was provided in this report.     

CdS/TiO2纳米晶薄膜的原位法制备及光电化学性能研究

CdS/TiO₂异质结薄膜因其优异的可见光催化性能, 在光催化领域引起了广泛关注。然而, 目前传统方法制备的CdS/TiO₂薄膜可能存在交界面结合不紧密的问题, 不利于光生载流子在交界面处的传输。因此, 本研究基于原位转换的原理(TiO₂→CdTiO₃→CdS), 将TiO₂纳米晶表层原位转换成CdS, 制备了CdS/TiO₂纳米晶薄膜。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)手段对样品薄膜的形貌和结构进行了表征。由表征结果可知, 在TiO₂纳米晶表面形成了CdS, 构成了交界面结合紧密的CdS/TiO₂异质结薄膜。光电化学性能研究表明, 与传统的连续离子层吸附反应法(SILAR)制备的薄膜相比, 原位法制备的CdS/TiO₂薄膜的光电流密度更高, 达到9.8 mA·cm^-2(V=0.4 V (vs. RHE)); 交流阻抗谱(EIS)结果表明, 原位法制备的CdS/TiO₂薄膜具有更小的电荷传输电阻, 说明原位法形成的CdS/TiO₂异质结结合更紧密, 能减小光生载流子在CdS/TiO₂界面处的传输阻力, 降低光生载流子在传输过程中的复合几率, 进而提高CdS/TiO₂薄膜的光电化学性能。     

Metal chalcogenide-oxide composite coatings prepared by spray pyrolysis

The spray pyrolysis technique has been employed to deposit composite coatings of chalcogenides of cadmium, zinc, lead and cobalt with oxides of aluminium, tin, lead, zinc and cobalt. Widely varying microstructural, electronic, optical and chemical properties have been obtained for such layers by monitoring the oxide composition, its spatial distribution and profile along the thickness. The large area chalcogenide-oxide composite films prepared by this technique are eminently suited for photovoltaic energy conversion, photothermal energy conversion and voltage-dependent resistor (Varistor) applications.In this paper we report our studies on co-pyrolytically deposited CdS:Al₂O₃ and CdS:SnO₂ layers and their application to improved thin film solar cells. Each of the oxides is insoluble in CdS and is segregated at the grain boundaries in the deposited films. Small amounts (less than 10%) of oxide in CdS are found to reduce its grain size negligibly and to make the film more compact, hard, adherent and less susceptible to chemical attack. The altered microstructure modifies the surface topography of the CdS film from a pebble-like roughness to an improved void-free serpentine texture. Segregated oxide in CdS does not affect the optical band gap of the films, although the composites exhibit enhanced diffuse optical scattering.Large area CdS films with a gradient profile of oxide have been utilized to fabricate thin film CdS/Cu₂S solar cells. The growth (length and distribution) of Cu₂S fingers and/or curtains deep into the top CdS layers during the topotaxial conversion reaction of chemiplating is controlled by the presence of oxide along the grain boundaries. This has not only resulted in improved interface topography for better carrier collection and reduced shunt losses but has also enabled us to decrease drastically the CdS film thickness necessary for the solar cells. Furthermore, the subsequent degradation of the junction via the well-known mechanism of the loss of copper from the Cu₂S layer by diffusion into CdS is expected to be considerably reduced by the presence of the oxide gradient in the CdS layer.     

Comparison of CdS thin films prepared by different techniques for applications in solar cells as window materials

CdS thin films as window materials for solar cells have been prepared by three procedures; chemical bath deposition, electrodeposition in an aqueous medium at 80 °C and electrodeposition in a non-aqueous medium at 170 °C. As deposited films along with those obtained after annealing in air at 400 °C for 15 min were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), glow discharge optical emission spectroscopy (GDOES), scanning electron microscopy (SEM), optical absorption spectra and photoelectrochemical spectroscopy (PEC) techniques under identical experimental conditions. X-ray diffraction data indicate the formation of hexagonal CdS as the predominent phase, but the SEM studies show that their textures are widely dependent on the conditions employed. GDOES profiling indicates the incorporation of Na and Si into CdS films prepared by all three techniques. Annealing of chemical bath deposited films causes a red shift of the absorbance edge and also a shift in the maxima of the photocurrent action spectra towards the low energy side. However, this effect was comparatively negligible for the samples prepared by the other two techniques. PEC studies indicate that CdS materials grown by all three techniques are all n-type. All studies indicate that the films grown at 170 °C using non-aqueous solutions are of better crystallinity and of improved electrical properties. © 1998 Kluwer Academic Publishers