Crystallite formation mechanism of CuIn(Se,S)2 synthesized using solvothermal method

This study developed a novel CuIn(S1−xSex)2 (CISS) crystal solvothermal synthesis method with a short reaction time. The ethylenediamine aqueous solution concentration, reaction temperature and time effects on crystal phase development and morphology were investigated. A single CISS phase with a crystallite size of about 200 nm can be synthesized using the solvothermal process using 50 vol% ethylenediamine aqueous solution as the solvent and sodium thioglycolate (TGA) simultaneously as a chelating agent, a reducing agent and the sulfur source at 200 °C for 3 h. The CISS nanocrystals formation mechanism using the solvothermal process can be divided into the following steps. The first step is Cu2−xSe phase formation at low reaction temperatures for short periods of time. Amorphous Inx(S,Se)y was formed as the reaction time was prolonged or the reaction temperature was raised. Cu2−xSe crystallites were then gradually dissolved into the solution by ethylenediamine. Copper ions then displaced indium ions by cation exchange reaction in amorphous Inx(S,Se)y particles, or occupied the vacant sites of indium ions to form CuIn(Se,S)2 crystals.