Sol-gel synthesis of Cu₂ZnSnS₄thin films under mild conditions

To produce the absorber layer material for thin-film solar cells, copper–zinc–tin sulfide Cu₂ZnSnS₄(CZTS) thin films were prepared from a sol-gel four-component solution in a simple, inexpensive, and environmentally friendly manner by directly applying it onto a glass substrate in multiple spin-coated layers. Afterwards, the resulting films were thermally processed in a drying oven under circulating air atmosphere without sulfur vapor. The obtained X-ray diffraction peaks exactly matched the CZTS (JCPDS 26−0575) diffraction pattern, indicating that the produced coatings were characterized by the kesterite structure. The calculated optical band gap energy of the obtained films was 1.45 eV, which was in good agreement with the literature values, thus suggesting their possible use as alternative candidate absorber materials. The obtained SEM images showed that the synthesized densely packed CZTS films with large sphere-like particles were compact and uniform. Therefore, we have shown for the first time in this study that nearly pure CZTS thin films can be obtained from solution through a one-step sol-gel process, which corresponds to non-toxic sulfurization at a relatively low heating temperature and non-vacuum conditions.