• Energy Research

Thin films of Cu2ZnSnS4 (CZTS) were prepared by sulfurization of multilayered precursors of ZnS, Cu, and Sn, changing the relative amounts to obtain CZTS layers with different compositions. X-Ray Diffraction (XRD), Energy Dispersive X-Ray spectroscopy, and SEM were used for structural, compositional, and morphological analyses, respectively. XRD quantitative phase analysis provides the amount of spurious phases and information on Sn-site occupancy. The optical properties were investigated by spectrophotometric measurements and Photothermal Deflection Spectroscopy. These films show a clear dependence of the optical and microstructural properties on the tin content. As the tin content increases we found: (i) an increase in both crystalline domain and grain size, (ii) an abrupt increase of the energy gap of about 150 meV, from 1.48 to 1.63 eV, and (iii) a decrease of sub-gap absorption up to two orders of magnitude. The results are interpreted assuming the formation of additional defects as the tin content is reduced.

AbstractCu2ZnSnS4 (CZTS) is a promising material for the production of thin film photovoltaic modules. In this paper we report on the fabrication and characterization of ZnO/CdS/CZTS/Mo solar cells. The CZTS absorber was grown by sulfurization of a precursor composed of a multilayer of ZnS, Sn and Cu. The CZTS structural, compositional and electronic properties were investigated by XRD, SEM-EDS, Raman spectroscopy and conductivity and mobility measurements. Solar cells with the structure ZnO/CdS/CZTS/Mo were produced and fully characterized. The problems connected to the back contact are investigated and discussed.

The optical absorption coefficient of thin film and bulk Cu2O at room temperature is obtained from an accurate analysis of their transmittance and reflectance spectra. These absorption spectra are modeled, together with the low temperature data reported in the literature, using an analytical expression to assess and quantify the role of the different absorption mechanisms. The results suggest that direct forbidden transitions and indirect transitions play an almost equally relevant role. A table of the optical constants of Cu2O single crystal is given for reference.

Corrigendum to ‘‘Absorption coefficient of bulk and thin film Cu2O’’ [Sol. Energy Mater. Sol. Cells 95(10) (2011) 2848–2854] Claudia Malerba , Francesco Biccari , Cristy Leonor Azanza Ricardo , Mirco D’Incau , Paolo Scardi , Alberto Mittiga a a ENEA, Casaccia Research Center, via Anguillarese 301, 00123 Roma, Italy b Department of Materials Engineering and Industrial Technologies, University of Trento, via Mesiano 77, 38123 Trento, Italy

Abstract The optical properties of sputtered Cu2O thin films doped with the nitrogen concentrations between 1 and 2.5 at% have been investigated by spectrophotometric measurements. All the doped samples exhibit two clearly defined absorption bands at energies below the gap, with an intensity well correlated with the N concentration. This result suggests Cu2O as a promising material for the development of intermediate band solar cells, also considering the band gap of about 2 eV which is the optimal value for this kind of devices. Moreover, the sample with the highest doping shows a resistivity of 1.14 Ω cm , which is the lowest value ever reported for this semiconductor. As a collateral result, we provide a first estimation of the Relative Sensitivity Factors (RSF) of nitrogen and oxygen atoms under Cs + bombardment in a Cu2O matrix.