From non-stoichiometric CTSe to single phase and stoichiometric CZTSe films by annealing under Sn+Se atmosphere.

One of the new materials for next-generation thin film solar cells is Cu 2 ZnSnSe 4 (CZTSe). However, achieving a single-phase CZTSe compound remains a challenge. This study describes the development of Cu 2 ZnSnSe 4 thin films through the sequential deposition of stacked films of non-stoichiometric Cu 2 SnSe 3 (CTSe) and ZnSe by magnetron sputtering. The structural, morphological, and electrical properties as well as the surface chemistry of the films were investigated and compared depending on the growth sequence of the thin films. By using Raman spectroscopy and grazing incidence X-ray diffraction, the tetragonal CZTSe structure was confirmed. Scanning electron microscopy and energy-dispersive spectroscopy measurements of the morphological and compositional properties indicated large grains and dense surfaces with an elemental composition close to the desired stoichiometry in SLG\SnSe 2 \Cu\ZnSe and SLG\SnSe 2 \Cu 2 Se\ZnSe stacks. To ascertain the surface chemistry and unique characteristics of the produced films, additional X-ray photoemission spectroscopy experiments were carried out. The optimal band gap values for the absorber layers were found using conventional spectroscopy, and they ranged from 0.88 to 1.47 eV. According to the electrical measurements, all the films were p-type and have high carrier concentrations between 1016 and 1020 cm−3. Our findings demonstrate that employing a sequential deposition approach and annealing in different atmospheres can yield CZTSe absorber layers with desirable properties, overcoming the challenge of non-stoichiometric CTSe precursors. [ABSTRACT FROM AUTHOR]