Claudia Malerba

Valence band offset at the CdS/Cu2ZnSnS4 interface probed by x-ray photoelectron spectroscopy

The valence band offset (VBO) at the interface CdS/Cu2ZnSnS4 was investigated by x-ray photoelectron spectroscopy (XPS). The VBO was measured by two different procedures: an indirect method involving the measurements of the core levels together with the XPS bulk valence band (VB) spectra and a direct method involving the analysis of XPS VB spectra at the interface. The indirect method resulted in a VBO value of (?1.20???0.14)?eV while the direct method returned a similar value of (?1.24???0.06)?eV but affected by a lower uncertainty. The conduction band offset (CBO) was calculated from the measured VBO values. These two measured values of the VBO allowed us to calculate the CBO, giving (?0.30???0.14)?eV and (?0.34???0.06)?eV, respectively. These values show that the CBO has a cliff-like behaviour which could be one of the reasons for the Voc limitation in the CdS/CZTS solar cells.

Stoichiometry effect on Cu2ZnSnS4 thin films morphological and optical properties

Thin films of Cu 2ZnSnS4 (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.

Chloride-based route for monodisperse Cu2ZnSnS4 nanoparticles preparation

A new approach based on hot injection method is proposed to gram-scale Cu2ZnSnS4 nanoparticles production minimizing the use of organic solvents. Nanocrystal synthesis was performed starting from metal chlorides and pure sulphur powder and using Oleylamine as capping agent. As a result, core-shell nanoparticles with a narrow size distribution were obtained.