Cu 2 ZnSnS 4 (CZTS) is a p-type semiconductor that has been seen as a possible low-cost replacement for Cu(In,Ga)Se 2 in thin film solar cells. So far compound has presented difficulties in its growth, mainly, because of the formation of unwanted phases like ZnS, Cu x SnS x+1 , Sn x S y , Cu 2−x S and MoS 2 . X-ray diffraction analysis (XRD), which is mostly used for phase identification cannot resolve some of these phases from the kesterite/stannite CZTS and thus the use of a complementary technique is needed. Raman scattering analysis can help distinguishing these phases not only laterally but also in depth. Knowing the absorption coefficient and using different excitation wavelengths in Raman scattering analysis, one is capable of profiling the different phases present in multi-phase CZTS thin films.This work describes in a concise form the methods used to grow chalcogenide compounds, such as, CZTS, Cu x SnS x+1 , Sn x S y and cubic ZnS based on the sulphurization of stacked metallic precursors. The results of the films' characterization by XRD, electron backscattered diffraction and scanning electron microscopy/energy dispersive spectroscopy techniques are presented for the CZTS phase. The limitation of XRD to identify some of the possible phases that can remain after the sulphurization process are investigated. The results of the Raman analysis of the phases formed in this growth method and the advantage of using this technique in identifying them are presented. Using different excitation wavelengths it is also analysed the CZTS film in depth showing that this technique can be used as non destructive methods to detect unwanted phases.

Abstract:In the present work we report the results of the growth, morphological and structural characterization of Cu 2 ZnSnS 4 (CZTS) thin films prepared by sulfurization of DC magnetron sputtered Cu/Zn/Sn precursor layers. The adjustment of the thicknesses and the properties of the precursors were used to control the final composition of the films. Its properties were studied by SEM/EDS, XRD and Raman scattering. The influence of the sulfurization temperature on the morphology, composition and structure of the films has been studied. With the presented method we have been able to prepare CZTS thin films with a kesterite structure.

Abstract:Thin film Cu 2 SnS 3 and Cu 3 SnS 4 were grown by sulfurization of dc-magnetron sputtered Sn-Cu metallic precursors in a S 2 atmosphere. Different maximum sulfurization temperatures were tested which allowed the study of the Cu 2 SnS 3 phase changes. For a temperature of 350 ºC the films were constituted by tetragonal (I-42m) Cu 2 SnS 3 . The films sulfurized at a maximum temperature of 400 ºC presented a cubic (F-43m) Cu 2 SnS 3 phase. Increasing the temperature up to 520 ºC, the Sn content of the layer lowered and orthorhombic (Pmn21) Cu 3 SnS 4 was formed.The phase identification and structural analysis was performed using X-ray Diffraction (XRD) and Electron Back-Scattered Diffraction (EBSD) analysis. Raman scattering analysis was also performed and the comparison with XRD and EBSD data allowed the assignment of peaks at

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Thin film solar cells based in Cu(In,Ga)Se2 (CIGS) are among the most efficient polycrystalline solar cells, surpassing CdTe and even polycrystalline silicon solar cells. For further developments, the CIGS technology has to start incorporating different solar cell architectures and strategies that allow for very low interface recombination. In this work, ultrathin 350 nm CIGS solar cells with a rear interface passivation strategy are studied and characterized. The rear passivation is achieved using an Al2O3 nanopatterned point structure. Using the cell results, photoluminescence measurements, and detailed optical simulations based on the experimental results, it is shown that by including the nanopatterned point contact structure, the interface defect concentration lowers, which ultimately leads to an increase of solar cell electrical performance mostly by increase of the open circuit voltage. Gains to the short circuit current are distributed between an increased rear optical reflection and also due to electrical effects. The approach of mixing several techniques allows us to make a discussion considering the different passivation gains, which has not been done in detail in previous works. A solar cell with a nanopatterned rear contact and a 350 nm thick CIGS absorber provides an average power conversion efficiency close to 10%.