Investigation of Cu2ZnSnS4 Formation from Metal Salts and Thioacetamide

Copper zinc tin sulfide (Cu2ZnSnS4, CZTS) is a very promising alternative to semiconductors based on Ga or In as solar absorber material. CZTS consists of abundant and cheap elements and in addition it displays very beneficial properties like a high optical absorption coefficient and an ideal band gap for photovoltaic applications. In this contribution, we present the preparation of thin films of copper zinc tin sulfide from metal salts (copper(I) iodide, zinc(II) acetate, and tin(II) chloride) and thioacetamide as sulfur source by a solution-based precursor method. The influence of synthesizing temperatures and concentration of thioacetamide in the precursor solution on the obtained CZTS materials was investigated. X-ray diffraction studies show that kesterite CZTS is formed. Depending on the temperature, nanocrystalline films with primary crystallite sizes from 8 nm (180 degrees C) up to approximately 150 nm (450 degrees C) were obtained. The early stages of the CZTS formation were monitored by time-resolved simultaneous grazing incident small- and wide-angle X-ray scattering (GISAXS, GIWAXS) analysis directly in thin layers revealing that the thermally induced reaction already starts at approximately 105 degrees C. The thin films exhibit high optical absorption (> 1 x 10(4) cm(-1)) and an optical band gap between 1.41 and 1.81 eV depending on the heat treatment. The obtained CZTS materials are of copper-poor and zinc-rich nature, which is ideal for the use in photovoltaic applications.