Characterization of Thin Films of CZTS using Transmission Electron Microscopy

The Kesterite (Cu 2 ZnSnS 4 ), named CZTS, is a potential semiconductor for use as an absorber layer in thin-film solar cells because of its optical and electrical properties. The basic materials for the synthesis of this semiconductor are not expensive and less toxic, compared to other candidates such as (CdTe and CIGS). However, the optimization of this material requires works to obtain the pure Kesterite structure, which is not stable after thermal annealing. This work concerns the development and characterization of CZTS thin films. The colloidal solution of CZTS was synthesized from metal chloride salts and thiourea, dissolved in methoxyethanol with ethylenediamine (EDA) as a stabilizer. The CZTS thin films were deposited on glass substrates by the sol-gel spin coating method. Then the samples were heated at 500°C, using a graphite box under vacuum with a small amount of sulfur for the sulfurization process. The microstructure of CZTS thin film were characterize by transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The Scanning transmission electron microscopy (STEM) images shows a homogeneous morphology.  Identification of the different crystallographic structure was realized by using electron diffraction patterns and Fast Fourier Transformation of High Resolution image (HRTEM). Meanly pure Cu 2 ZnSnS 4 crystallites were found with some secondary phase such as SnO 2 . With this work, it is shown that films deposited by spin coating and sulfurized at 500°C under vacuum with solid sulfure, are Kesterite structure of Cu 2 ZnSnS 4 with some residual phases of SnO 2 Cassiterite. Keywords: Kesterite, CZTS, TEM, Thin films, Solar cells