The preparation of ultra-thin semi-transparent solar cells with potential applications in windows or transparent roofs entails several challenges due to the very small thickness of the layers involved. In particular, problems related to undesired inter-diffusion or inhomogeneities originated by incomplete coverage of the growing surfaces must be prevented. In this paper, undoped SnO2, CdS, and CdTe thin films with thickness suitable for use in ultra-thin solar cells were deposited with a radiofrequency (RF) magnetron sputtering technique onto conductive glass. Preparation conditions were found for depositing the individual layers with good surface coverage, absence of pin holes and with a relatively small growth rate adapted for the control of very small thickness. After a careful growth calibration procedure, heterostructured solar cells devices were fabricated. The influence of an additional undoped SnO2 buffer layer deposited between the conductive glass and the CdS window was studied. The incorporation of this layer led to an enhancement of both short circuit current and open circuit voltage (by 19 and 32%, respectively) without appreciable changes of other parameters. After the analysis of the cell parameters extracted from the current-voltage (I-V) curves, possible origins of these effects were found to be: Passivation effects of the SnO2/CdS interface, blocking of impurities diffusion or improvement of the band alignment.

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In this work, we present the preparation of CdS nanowires (CdS NWs) using the chemical vapor deposition technique and bismuth (Bi) nanoparticles as catalysts. The obtained nanowires were found to be in the hexagonal Greenockite structure according to XRD diffractograms and Raman spectroscopy measurements. Depending on the growth temperature, two kinds of morphologies were observed in SEM images. At low temperature (around 150 • C), a high density and homogeneous population of thin and straight nanowires grown through the vapor-liquid-solid mechanism was observed. At higher temperature (around 270 • C), thicker bunches of braided nanowires were observed. A quantitative analysis of the temperature-dependent photoluminescence spectra of the CdS NWs was carried out.

Graded composition CdxZn1-xTe films were prepared by growing several alternate layers of CdTe and ZnTe by the Isothermal Close Space Sublimation technique. The thickness of both kinds of layers was modified along the structure to produce an increase of the average concentration of CdTe towards the surface of the films. Due to Zn/Cd inter-diffusion during the growth process the sequence of layers was converted into a relatively smooth graded composition film. According to X-ray diffraction characterization the layers grew coherently with the (100) oriented GaAs substrates although they showed a relatively high mosaicity. 2 plots show very wide diffraction peaks as expected from variable composition samples. The band gap grading effect in light absorption was also verified through transmission measurements, using transparent substrates. Graded composition profiles of the thin films were confirmed by x-ray photoelectron and secondary ion mass spectroscopies. Moreover, quantitative Cd, Zn and Te profiles were obtained by the analysis of Rutherford backscattering spectra of the samples. This analysis showed a CdTe molar fraction profile ranging from approximately x = 0.8 at the surface of the sample and x = 0.35 at the interface with the substrate. The possibility of growing graded composition layers using a simple and cost-effective procedure was demonstrated. This could be interesting in technological applications like CdxZn1-xTe layers of variable composition in CdS/CdTe solar cells.