Insights into the exceptional stability of the molecular precursor solution for Cu₂ZnSnS₄ solar absorber

Environment friendly molecular precursors are extensively studied for green, economical and scalable fabrication of inorganic thin films for various device applications. For compound semiconductors such as the chalcogenide solar absorber Cu₂ZnSnS₄ (CZTS), the stability of such precursor solution is highly sought after. The longer shelf life of the precursor could significantly improve the phase purity as well as the reproducibility of the resulting films, and also would aid the industrial scaling up of the fabrication process. Herein, the reason behind the exceptional stability shown by a precursor solution for CZTS is explored, by probing the nature of interaction between its various components. The unique combination of solvent and the sulfur source is shown as favorable for the stable bonds in the solution, especially the predominant bidentate bridging of sulfur source to the metal atoms. The insights elucidated through simple spectroscopic techniques can be handy when designing such sustainable precursors for other functional chalcogenides and technologically important inorganic compounds.