Arturo Morales-Acevedo

Characterization of CuInS2 thin films for solar cells prepared by spray pyrolysis

Abstract We have made a study of the chemical composition, the electrical, the optical and the structural properties of polycrystalline CuInS2 thin films prepared by spray pyrolysis to be used for thin film solar cells. These films were deposited starting from aqueous solutions with different chemical compositions ([Cu]/[In] and [S]/[Cu] ratios) and at different substrate temperatures. In all cases, the material is p-type with grains preferentially oriented in the (112) direction of the sphalerite structure. The electro-optical properties show a very strong dependence on the [Cu]/[In] ratio in the solution. Films with copper excess have smaller resistivity and better crystallinity than those which are stoichiometric or have indium excess. The results obtained in this work show the possibility of having CuInS2 thin films with a wide range of resistivity, a fact that could be important for making solar cells based on this material.

Optoelectronic properties of CdO/Si photodetectors

Abstract CdO/Si heterojunctions were fabricated by depositing CdO polycrystalline thin films on p-type single crystalline silicon wafers by CBD. The current–voltage characteristics under dark and illumination of CdO/Si devices resemble those of a light sensitive diode. From the CdO/Si diode spectral sensitivity curves (A/W), it has been implied that CdO films allow a high sensitivity response in the visible and the near infrared regions.

Spray pyrolysis deposition of cadmium–zinc oxide thin films

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.

F-doped CdO thin films deposited by spray pyrolysis

Thin films of CdO were prepared by spray pyrolysis using cadmium acetate as the Cd source. The films were intentionally doped with fluorine by adding NH 4 F in the solution. The substrate temperature was varied in the range from 170 to 290°C while keeping the other deposition parameters constant, except the NH 4 F concentration in the solution, which was varied up to 8 wt%. The structural, optical, and electrical properties of the films were studied in order to obtain, under our experimental conditions, optimal values for the NH 4 F concentration and substrate temperature. We show that the best deposition conditions for a photovoltaic application of the films are substrate temperature T s = 210 °C and NH 4 F concentration around 4%.

Influence of post-thermal annealing on the properties of sprayed cadmium–zinc oxide thin films

Abstract We have prepared (ZnO)x(CdO)1−x thin films by spray pyrolysis. Mixed thin film oxides with different compositions of cadmium and zinc were deposited on glass substrates and exposed to different annealing treatments at a fixed temperature. The effects due to post-thermal annealing on the structural, optical and electrical properties of the variable composition thin films have been studied depending upon the x value. The crystalline structure was studied by X-ray diffraction (XRD). We found the presence of CdO XRD patterns for low Zn concentrations, and a mixing of CdO (cubic) and ZnO (hexagonal) phases for low Cd concentrations. In all cases, the crystallite sizes increased with the annealing. In addition, the band-gap and the resistivity vary between those found for pure CdO and ZnO. The changes of the latter parameters with the post-thermal annealing are studied also as a function of the x value.

Chemical composition and electrical conduction mechanism for CdO:F thin films deposited by spray pyrolysis

Interest in CdO is growing thanks to its potential use in different optoelectronic devices. Doping with fluorine has effectively improved its electro-optical properties. An analysis of the composition and electrical conduction mechanism of CdO:F films deposited by spray pyrolysis is made. Film properties result from the combined effect of oxygen substitution and oxygen vacancy occupation by fluorine atoms. Carrier scattering seems to be due to phonons and ionized or neutral impurities.

Properties of CdS thin films chemically deposited in the presence of a magnetic field

Abstract 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.

Physical properties of AgInS2 films prepared by chemical spray pyrolysis

Abstract We have prepared AgInS2 thin films by the spray pyrolysis technique. The effects of the growth temperature and the chemical composition of the solution on the structural, optical and electrical properties of the films have been studied. It was found that growth temperatures above 400°C lead to single-phase chalcopyrite type AgInS2 films, but deposition temperatures lower than 400°C lead to mixed chalcopyrite and orthorombic structure films. All the films grown here show n-type conductivity, with room temperature resistivity in the range between 103 and 105 Ω cm. The absorbance derivative spectra of single-phase AgInS2 films revealed two optical energy gaps at approximately 1.87 and 2.03 eV, attributed to the fundamental edge and to the valence band splitting by the crystal field, respectively.

New window materials used as heterojunction partners on CdTe solar cells

Abstract 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).

Improving the efficiency of CdS/CdTe solar cells by varying the thiourea/CdCl2 ratio in the CdS chemical bath

In this work, the influence of the properties of CdS thin films grown by chemical bath deposition upon the characteristics of CdS/CdTe solar cells, when varying the thiourea concentrations in the CdS bath solution, is studied. The important solar cell parameters such as short circuit current (Jsc), open circuit voltage (Voc), fill factor (FF) and efficiency (η) were measured and it was noted that they improve for thiourea/CdCl2 ratios (in the CdS deposition solution) up to 5, and drop for higher ratios in the range investigated. In addition, the ideal diode factor (n), saturation current (Jo) and series resistence (Rs) were studied under illumination and dark conditions. The results could be related to several factors, among them, the photoconductivity properties of the layers and the change of the CdS1−xTex layer at the CdS–CdTe interface.