Simple and facile synthesis of a CuS film using a copper formate–thioacetamide complex ink

In this study, we developed a simple and facile synthesis method for producing CuS films at low temperatures. The method uses self-reducible complex inks comprising copper formate (Cuf) as the copper source and thioacetamide (TA) as both the sulfur source and complexing agent. The thermal properties of complex inks with different TA/Cuf ratios (0.5–2.0) were analyzed. The ink with a TA/Cuf ratio of 1 exhibited a significant decrease in the reduction temperature. The synthesis of a CuS film involved calcination of the ink at 140 °C; however, some residual Cuf was observed. Introducing hexanol to the ink, aimed at prolonging the liquid-phase reaction, yielded a pure CuS film that contained agglomerated particles. The thermal reduction pathway of Cuf to CuS was analyzed through thermogravimetric–mass spectrometric analysis, and the results revealed that the low-temperature synthesis was attributed to the formation of acetonitrile and formic acid during thermal decomposition of the ink.