Crystal size-controlled growth of Cu2ZnSnS4 films by optimizing the Na doping concentration

• CZTS films was deposited by a novel and direct Na-containing precursor solution method.
• 1.0% Na doping can well enhance the particles size and crystallinity of CZTS films.
• 1.0% Na doping can well enhance the electrical conductivity of CZTS films.
• This Na containing method may be used to form CZTS films on other flexible substrates.

Solution-based approach is a simple method to deposit Cu2ZnSnS4 (CZTS) films, which is one of the most promising materials for low-cost thin film solar cells. In this work, a novel Na-containing precursor solution using ethylene glycol as solvent was used to deposit CZTS films on Na-free substrate. Effects of various Na concentrations on the properties of CZTS films were systematically studied. The results show that the 1.0% Na-doping can well enhance the growth of particle size, has the highest crystallinity and electrical conductivity, and its band gap is 1.55 eV, which is appropriate band gap to solar cells. This Na-containing method can well control the concentration of Na and it may be used to form CZTS thin films on other flexible substrates other than soda-lime glass.