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In this paper, we report results on the processing of cadmium zinc sulfide (CdxZn1-xS) ternary compound starting from the deposition of cadmium sulfide (CdS)/zinc sulfide (ZnS) bi-layers buffer configuration and a subsequent thermal annealing for its application to thin film solar cells. The impact of different CdS/ZnS bi-layers buffer configurations as effective alternative to the single CdS buffer layer, as well as the physical and chemical properties of the equivalent CdxZn1-xS ternary compound are presented and discussed. Results on physical properties optimization of CdxZn1-xS ternary compound for future applications to thin film solar cells are presented.

A simple and inexpensive technique to synthesize and deposit Cu(II) oxide (CuO) nanostructured layers is reported herein together with electrical and optical properties characterization. The 2-step deposition procedure consists of spin-coating a Cu(II) formate solution on fluorine-doped tin oxide (FTO) conducting glass substrate followed by a heat treatment. Fluorescence spectroscopy and Fourier transform infrared spectroscopy confirmed that the organic ligand precursor is absent in the obtained film. X-ray diffraction (XRD) experiments show that only CuO films are deposited on the FTO substrate ruling out the presence of other Cu x O oxides. Scanning-electron microscopy reveals their nanostructured morphology; which agrees with crystallite size domain (L = 21 nm) estimated from XRD width peak analysis. Absorption coefficient spectra, as well as direct-gap values (E g = 1.52–1.55 eV), were obtained using optical transmittance and reflection spectroscopy. Finally, the as prepared CuO films are used as photoelectrodes in a photoelectrochemical cell with an aqueous electrolyte and short-circuit photocurrent under illumination and dark conditions is measured.

We report the structural and microstructural features of Bi 2 Te 3 films deposited by close space vapor transport (CSVT) technique on soda-lime glass substrates. Different phases are obtained depending on the substrate temperature, as well as changes in the thermoelectric properties of the CSVT-Bi 2 Te 3 films. The relationship between the structural and electrical properties of the films is present.

The chemical etch of CdTe surfaces with a mixture of phosphoric and nitric acids is used in research labs in order to enhance the back-contact formation in CdS/CdTe solar cells. However, the possible passivation effect of this approach has not been studied. In this work we report an investigation about the etching effect of nitric/phosphoric acid mixtures with different etching times (0, 30, 40 and 50 s) and variable concentrations of the nitric acid upon the surface recombination velocity of CdTe films deposited by close space vapor transport. Surface recombination velocities with values as low as 93 cm/s were achieved.

Cu/TiO2 composite films were prepared at low temperature on glass substrates by a photodeposition method. Films were deposited by irradiating the substrate while in contact with an aqueous TiO2 suspension containing copper(II) nitrate and ethanol. Cu/TiO2 composite films of 500 nm in thickness were deposited at room temperature after a short irradiation time (15 min) with a 125 W mercury vapour lamp. According to scanning electron microscopy observations, the obtained films were homogeneous and porous. Energy dispersive X-ray spectroscopy analysis revealed a 3:1 Cu:Ti atomic ratio. Grazing angle X-ray diffraction analysis showed that the films contained Cu and TiO2 as major components and Cu2O as a minor component. Heat treatment at 400 °C in air for a period of 3 h transformed the initial material into a CuO/TiO2 composite, improved the adhesion to the substrate and favoured a more regular distribution of copper oxide according to backscattering micrographs.

Studies on chemical bath deposited CdS bi-layers are reported. The deposition process consisted in depositing first a CdS layer at 75 °C for 10 min and then a second CdS film was deposited at 40 °C for 45 min to form the bi-layer. By depositing the second CdS film at a lower temperature we could increase the surface covering which allows us to have a better control of the kinetics of the bi-layer growth. In this work, four different structures were prepared and their optical properties studied. Prototype CdTe/CdS devices were developed using these samples. Results of the spectral response and the photovoltaic parameters of these four different structures of CdS/CdTe solar cells are presented and discussed.

Bi doped cadmium telluride (CdTe:Bi) thin films were grown on glass-substrates by the close space vapour transport method. CdTe:Bi crystals grown by the vertical Bridgman method, varying the nominal Bi concentration in the range between 1×1017 and 8×1018 cm−3, were used in powder form for CdTe:Bi thin film deposition. Dark conductivity and photoconductivity measurements in the 90–300 K temperature range and determination by photoacoustic spectroscopy of the optical-absorption coefficient of the films in the 1.0 to 2.4 eV spectral region were carried out. The influence of Bi doping levels upon the intergrain barrier height and other associated grain boundary parameters of the polycrystalline CdTe:Bi thin films were determined from electrical, optical and morphological characterization. © 2007 Elsevier B.V. All rights reserved

In previous papers we have reported the improvement of the efficiency of CdS/CdTe solar cells by varying the thiourea/CdCl 2 ratio ( R tc ) in the chemical bath solution used for the deposition of the CdS layers. In this work, a more complete study concerning the physical properties of Chemical Bath Deposited (CBD) CdS layers studied by photoluminescence, X-ray diffraction and optical spectroscopy are correlated to the I – V characteristics under AM 1.5 sunlight and the spectral response of CdS/CdTe solar cells. It is confirmed that the optimum R tc for the CBD CdS films is R tc = 5, since in this case the best solar cells were obtained and these films show the better optical and structural characteristics.

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 (Jsc), open circuit voltage (VOC), 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.

In this work, we present studies of photoluminescence at room temperature of CdS films grown by the chemical bath deposition technique. Usually, as-grown CdS-CBD samples do not show luminescence at room temperature because of the high density of recombination centers due to many defects generated during the growth process. The change of the S/Cd ratio allows to control the density of defects giving rise to a better quality CdS-CBD films, which can show luminescence at room temperature. Depending on the S/Cd ratio, an evolution and improvement of the photoluminescence signal at room temperature is observed.

A soft and simple photochemical technique is proposed for the incorporation of copper oxide to nanoporous TiO 2 with the purpose of sensitizing the TiO 2 to wavelengths in the visible range. An aqueous solution of copper formate is employed as precursor. The light intensity value needed for the process, as well as its spectral range, is readily attainable with solar light. Because of the importance of heterojunctions of porous semiconductors in solar energy application, like extremely thin absorber solar cells, experimental conditions have been studied in order to obtain a thin absorption layer of copper oxide covering the TiO 2 . Selection of copper formate solution concentration, irradiation time and previous immersion time in the precursor solution has been studied using X-ray diffraction, scanning electron microscopy and optical spectral transmission. Direction and wavelength dependence of photocurrent show that photons are absorbed by the copper oxide and electrons injected to the TiO 2 .

ZnO films have been obtained by a modification of the chemical bath deposition (CBD) procedure in which crystal growth is activated using microwave (MW) radiation. ZnO films has been grown on F-doped SnO2-covered glass substrates immersed in an aqueous solution which contains a soluble zinc oxide precursor (zinc nitrate or zinc acetate) and urea or hexamethylenetetraamine to promote the formation of the oxide. This new method, MW-CBD, produces well-adhered films at low temperatures, in an open atmosphere and in short times. The deposited material is crystalline and, thus, no additional heat treatment is necessary. The degree of coverage and the shape of the ZnO nanocrystallites are determined by the composition of the chemical bath and by the MW radiation power and irradiation time. A suitable selection of these parameters allows attaining complete substrate coverage with ZnO nanorods, mainly oriented perpendicularly to the substrate, in only 12 min.

We study the effects of thiourea concentration on CdS thin films deposited by chemical bath deposition (CBD), submitted to post-thermal treatments of CdCl2, and its effect on the characteristics of CdS/CdTe solar cells. We compare these cells with similar ones fabricated with CdS-films grown by Close Space Vapor Transport (CSVT). The CBD-CdS cells shows higher open circuit voltage (Voc) and fill factor (FF), while the short circuit current remains with little change, as the ratio of S to Cd in the CBD solution goes from 1 to 5. This dependence changes when there is a variation of the CBD-CdS layer thickness. We have obtained cells with more than 12% efficiency when the CdS layers are deposited by the best CBD condition (S/Cd=5) as compared to the best cells with CdS layers prepared by CSVT that had 11% efficiencies. Other measurements such as spectral response were performed and their results were correlated to the I–V characteristics of the solar cells so that the best performances of CBD-CdS solar cells are explained in terms of the chemical composition of this layer.

TiO2 layer films were grown using the microwave (MW)-activated chemical bath deposition technique on two different indium tin oxide substrates. The TiO2 films are studied to determine their structural response when changing the MW heating power. Thickness (areal density), oxygen concentration profile, composition and surface homogeneity were determined using Rutherford backscattering spectrometry, nuclear reaction analysis and atomic force microscopy. The analysis showed that the composition, thickness and surface structure of the films are highly influenced by MW heating power. The substrate, acting as seed for nucleation, influences the layer thickness, indicating that a thinner layer of TiO2 is obtained for the more conducting substrates. The oxygen concentration profile is constant in the TiO2 layer at low MW heating, power (≈20%). The rugosity of the samples and the non-homogeneity increase with the MW heating power. If the MW heating power is high enough pinholes in the TiO2 layer of the order of the sample thickness are produced.

Optical and structural characterization of ZnS thin films grown by chemical bath deposition (CBD), introducing for the first time a magnetic field (MF), are reported. Corning glass as well as Si and GaAs single crystals were used as substrates. The effect of H2-annealing, in the range of temperature 200–300 °C, and MF on the morphology and crystalline structure of films is studied in atomic force microscopy images and in X-ray diffractograms. MF does not manifest appreciable influence on the grain size (GS) when glass substrates are used. On the contrary GS diminishes noticeably when MF is applied on ZnS/Si and ZnS/GaAs CBD-growths. Further, an improvement of the optical properties with post-growth annealing in H2, as exhibited by optical transmission, is obtained. An application of these ZnS films as antireflective coating is analyzed by reflectance spectra.

TiO 2 films were deposited on either glass or Si substrates by using a two-step soft-solution method. A submonolayer of anatase TiO 2 nanocrystals was first deposited on the substrate by a drain-coating process that was performed at 333 K from an aqueous TiO 2 colloidal solution. The substrate partially covered with the TiO 2 nanocrystals was immersed in an aqueous solution, containing a titania precursor [fluorine-complexed Ti(IV)], and the whole was treated with microwave irradiation. The nanocrystals deposited on the substrate acted as growth seeds in the subsequent formation of the TiO 2 film. The obtained TiO 2 films showed a high degree of crystallinity (anatase), even without further thermal treatment; however, they did not show photocatalytic activity. Thickness of the films was varied as a function of microwave power and irradiation time.

We present in the results of this work, the influence of oxygen and the gradient of temperature in the processing of CdTe thin films, by using the close space vapor transport (CSVT) technique. In general the kinetic process is strongly influenced by these parameters; where a reduction in the growth rate, grain size; an increase in the intergrain barrier height; and structural changes are present.

Polycrystalline thin film CdS/CdTe heterojunction solar cells are important candidates for large scale photovoltaic applications. In this work we use a C–V (capacitance vs. voltage) theoretical method for the determination of the interface charge density σ and band discontinuity ΔEv of the CdS/CdTe heterojunction. The methodology is based on three cardinal equations: i) line up of the bands relative to the common Fermi level (at equilibrium) or the quasi-Fermi level (when voltage is applied), ii) charge neutrality and iii) the total capacitance of the heterostructure. We used CdS/CdTe solar cells, grown in our laboratory by the chemical bath deposition (for CdS film) and the close space vapor transport (for CdTe film) techniques. The interface parameters σ, and ΔEv are determined from C–V fitting between the calculated and the measured curve. The methodology presented in this study is general and can be applied to semiconductor–semiconductor and semimetal–semiconductor heterojunctions.

A new method has been devised for the deposition of TiO2 thin films on conducting glass using a microwave reactor. The substrates are immersed in a diluted homogeneous aqueous solution which was prepared by mixing equal volumes of a fluorine-complexed titanium(IV) solution ([Ti]=3.4×10−2 M) and 6.8×10−2 M boric acid solution. Low microwave power and short deposition time have been used. The TiO2 layers obtained are well-adhered, homogenous, with good specularity and colored by interference of reflected light. Their thickness is in the range of 100–500 nm. SEM experiments denote that films are formed by small crystallites having linear dimensions under 100 nm. Crystal dimensions depend on microwave power and deposition time. The layers show a high degree of crystallinity and the observed crystal phase is anatase. Microwave heating has proved to be an efficient and inexpensive method for solution growth of TiO2 films; it should also be of importance for other materials layers grown from solution.

We present in this work the processing and characterization of two semiconductor thin films (ZnS and Zn x Cd 1− x O) grown by chemical bath deposition (CBD), and used as heterojunction partners on CSVT-CdTe films. The photovoltaic properties of the Zn x Cd 1− x O/CdTe heterojunction are reported here for the first time. The analysis of the basic properties of the films was carried out by standard optical and electrical characterization techniques. The heterojunction systems were studied by means of I–V characteristics, spectral response and quasi-static C–V measurements. Short-circuit currents of 8.9 and 22 mA/cm 2 , open-circuit voltages of 0.489 V and 0.324 V, fill factors of 0.29 and 0.42 and conversion efficiencies of 1.26 and 3.12% were obtained for SnO 2 /Zn 0.9 Cd 0.1 /CdTe and SnO 2 /ZnS/CdTe, respectively, under normalized 100 mW/cm 2 illumination (AM1).

The controlled increase of hole concentration is an important issue and still an unsolved problem for polycrystalline CdTe-based solar cells. The typical hole concentration of as-grown CdTe thin-films goes up to 10 13 cm − 3 , depending on the specific growth technique. The highest electron concentration obtained for CdS, the suitable window partner material of CdTe, is around 10 15 cm − 3 . Thus, the PV-performance of a CdS/CdTe device can be optimized if the hole concentration in CdTe is increased. We have faced up this problem by studying the electrical properties of two types of CdTe films: CdTe films grown by Close Space Vapor Transport using a CdTe:Bi powder as the starting material and CdTe sputtered films doped by implantation with different Bi-doses. Temperature-dependent resistivity and Hall effect measurements and a discussion on the efficiency of both doping processes are presented.

CdS films were grown on glass substrates by chemical bath deposition (CBD) technique using CdCl2 as the Cd ions and thiourea as the S ions source. The films were grown with and without the influence of a constant D.C. magnetic field. The magnetic field (B) was applied perpendicular and parallel to the substrate and the film depositions were carried out at different fixed B intensity values. Various properties of the films, such as optical transmission, dark resistivity, surface morphology and the X-ray diffraction patterns were studied as a function of magnetic parameters. In the present work preliminary results are presented and discussed.

A study of the influence of some growth parameters, the gradient of temperature between source and substrate and introduction of oxygen in the growth chamber, on the optical properties of CdTe thin films grown by Close Space Vapor Transport (CSVT) is presented. This study was carried out by means of photoluminescence (PL). The combined effect of the temperature gradient and oxygen in the growth chamber on the crystalline quality of CdTe thin films were analyzed. Important changes in the photoluminescence spectra were observed. A decrease of the intensity of the excitonic PL band is observed, as oxygen concentration increases. This accounts for an increase in the defect density due to the presence of oxygen.

Mixed thin film oxides of cadmium and zinc with different compositions were deposited on glass substrates by spray pyrolysis. The effect of the various parameters on the growth and on the film properties is presented. The sample structure was studied by X-ray diffraction (XRD) having found the presence of a cubic phase resembling that of pure CdO XRD pattern for low Zn concentrations. For x=0.75 a low crystallinity of the ZnO structure was observed. Optical band-gap was also studied from optical transmittance measurements. As expected, the band-gap values change between those of pure CdO and those of ZnO.