Mauricio Ortega-López

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.

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.

Optical and structural characterization of oleic acid-stabilized CdTe nanocrystals for solution thin film processing

Summary This work presents results of the optical and structural characterization of oleic acid-stabilized cadmium telluride nanocrystals (CdTe-NC) synthesized by an organometallic route. After being cleaned, the CdTe-NC were dispersed in toluene to obtain an ink-like dispersion, which was drop-cast on glass substrate to deposit a thin film. The CdTe-NC colloidal dispersion as well as the CdTe drop-cast thin films were characterized with regard to the optical and structural properties. TEM analysis indicates that the CdTe-NC have a nearly spherical shape (3.5 nm as mean size). Electron diffraction and XRD diffraction analyses indicated the bulk-CdTe face-centered cubic structure for CdTe-NC. An additional diffraction line corresponding to the octahedral Cd3P2 was also detected as a secondary phase, which probably originates by reacting free cadmium ions with trioctylphosphine (the tellurium reducing agent). The Raman spectrum exhibits two broad bands centered at 141.6 and 162.3 cm−1, which could be associated to the TO and LO modes of cubic CdTe nanocrystals, respectively. Additional peaks located in the 222 to 324 cm−1 range, agree fairly well with the wavenumbers reported for TO modes of octahedral Cd3P2.

Development of highly faceted reduced graphene oxide-coated copper oxide and copper nanoparticles on a copper foil surface.

Summary This work describes the formation of reduced graphene oxide-coated copper oxide and copper nanoparticles (rGO-Cu2ONPs, rGO-CuNPs) on the surface of a copper foil supporting graphene oxide (GO) at annealing temperatures of 200–1000 °C, under an Ar atmosphere. These hybrid nanostructures were developed from bare copper oxide nanoparticles which grew at an annealing temperature of 80 °C under nitrogen flux. The predominant phase as well as the particle size and shape strongly depend on the process temperature. Characterization with transmission electron microscopy and scanning electron microscopy indicates that Cu or Cu2O nanoparticles take rGO sheets from the rGO network to form core–shell Cu–rGO or Cu2O–rGO nanostructures. It is noted that such ones increase in size from 5 to 800 nm as the annealing temperature increases in the 200–1000 °C range. At 1000 °C, Cu nanoparticles develop a highly faceted morphology, displaying arm-like carbon nanorods that originate from different facets of the copper crystal structure.

Green Routes for Graphene Oxide Reduction and Self- Assembled Graphene Oxide Micro- and Nanostructures Production

Graphene-derived materials are currently studied because of their actual and projected applications. Among them, graphene oxide (GO) promises for outstanding applications as it can be prepared at large scale by simple, scalable, and low-cost techniques. The existent chemical methods based on the graphite exfoliation (phase solution and Hummers based) produce highly functionalized graphene, i.e., GO-like materials that converts into reduced GO (rGO) after a reduction treatment. The present work presents the current scenario on the GO green reduction methods, on the development of hierarchical carbon-based structures by the self-assembly of GO sheets at interfaces, and on rGObased hybrid nanocomposites. It is worth noting that, to date, the production and application of graphene-related materials are the fastest-growing research areas.

A simple method for the deposition of nanostructured tellurium synthesized in ammonia solution

In this work, we report a highly adherent, and uniform deposition of nanostructured tellurium. The deposition of the nanostructured tellurium was realized by the dripping of a modified solution of NaHTe based on the dissolution of NaBH4 and tellurium powder in an aqueous solution of NH4OH. This method allowed the relatively simple manipulation of tellurium nanostructures under laboratory ambient, without requiring the use of organic stabilizers. Transmission electron microscopy (TEM) was realized on a powder sample obtained by the reaction between H2Te and aqueous solution of NH4OH. TEM analysis indicated that tellurium nanorods and Y-type nanostructures are grown from tellurium nanoparticles, such as in a hydrothermal system. Then, the nanoparticles serve as seeds for the growth of more extended tellurium nanostructures. Electron diffraction and X-ray diffraction analysis showed that depositions have the hexagonal structure of tellurium highly oriented on (101) direction.

Properties of AgInS/sub 2/ films prepared by spray pyrolysis for solar cells

The authors have prepared AgInS/sub 2/ thin films by the spray pyrolysis technique. The effects of the growth temperature and the chemical composition of the solution upon the structural, the optical and the electrical properties of the films have been studied. It was found that growth temperatures above 400/spl deg/C lead to single-phase chalcopyrite type AgInS/sub 2/ films, but deposition temperatures lower than 400/spl deg/C lead to mixed chalcopyrite and orthorombic structure films. All the films grown here show n-type conductivity with room temperature resistivities in the range between 10/sup 3/-10/sup 5/ /spl Omega/-cm. The absorbance derivative spectra of single phase AgInS/sub 2/ films revealed two energy gaps around 1.87 eV and 2.03 eV, attributed to the fundamental edge and to the valence band splitting by the crystal-field, respectively.