C. Calderón

XPS analysis and structural characterization of CZTS thin films prepared using solution and vacuum based deposition techniques

This work describes a procedures to grow single phase Cu2ZnSnS4 (CZTS) thin films with tetragonal-kesterite type structure, using solution and vacuum based deposition techniques. The solution based deposition approach involves sequential deposition of Cu2SnS3 (CTS) and ZnS films, where the CTS compound is synthesized in one step process by simultaneous precipitation of Cu2S and SnS2 performed by diffusion membranes assisted CBD technique and the vacuum based approach includes sequential evaporation of the elemental metallic precursors under a flux of sulphur supplied from an effusion cell. X-ray diffraction analysis (XRD) which is mostly used for the phase identification can not clearly distinguish the formation of secondary phases such as Cu2SnS3, since both compounds have the same diffraction pattern; therefore the use of a complementary technique is needed. Raman scattering analysis was used to distinguish these phases. Further, the chemical elemental composition and oxidation states of both type of CZTS films were studied by X-ray photoelectron spectroscopy (XPS) analysis.

Novel Chemical Route for Deposition of Cu2ZnSnS4 Photovoltaic Absorbers

This work reports results of a study carried out to optimize the preparation conditions of Cu2ZnSnS4 (CZTS) thin films grown by sequential deposition of Cu2SnS3 (CTS) and ZnS layers, where the Cu2SnS3 compound was grown using a novel procedure consisting of simultaneous precipitation of Cu2S and SnS2 performed by diffusion membrane assisted chemical bath deposition (CBD) technique. The precipitation across the diffusion membranes allows achieving moderate control of release of metal ions into the work solution favoring the heterogeneous growth mainly through an ion-ion mechanism. Through a parameters study, conditions were found to grow Cu2SnS3 thin films which were used as precursors for the formation of Cu2ZnSnS4 films. The formation of CZTS thin films grown in the Cu2ZnSnS4 phase was verified through measurements of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Solar cells with efficiencies of 4.9% were obtained using CZTS films prepared by membrane assisted CBD technique as absorber layer.