Cu2ZnSnS4 thin films obtained by sulfurization of evaporated Cu2SnS3 and ZnS layers: Influence of the ternary precursor features

摘要

Cu2ZnSnS4 (CZTS) thin films have been grown by sulfurization of Cu2SnS3 (CTS) and ZnS layers evaporated on glass substrates. Four CTS precursor films have been tested, with two different atomic compositions (Cu/Sn = 1.7 and Cu/Sn = 2.1) and substrate temperatures (350 and 450 degrees C), together with analogous ZnS layers deposited by maintaining the substrate at 200 degrees C. The sulfurization of the CTS and ZnS stacked layers was performed at 500 degrees C during 1 h. The evolution of the crystalline structure, morphology, optical and electrical properties from each CTS precursor to the CZTS compound has been studied, especially the influence of the ternary precursor features on the quaternary film characteristics. The kesterite structure has been identified after sulfurization of the various samples, with main (112) orientation and mean crystallite sizes S-112 =40-56 nm, being higher for the Cu-poor compositions. The CZTS average roughness has varied in a wide interval R-a = 8-66 nm, being directly related to the CTS precursor layer, which becomes rougher for a higher deposition temperature or Cu content. Besides, the band gap energy and the electrical resistivity of the CZTS films have changed in the ranges E-g = 1.54-1.64 eV and rho = 0.2-40 Omega cm, both decreasing when the Cu content and/or the surface roughness increase. (C) 2016 Elsevier B.V. All rights reserved.