Synthesis and characteristics of Cu(In,Ga)Se₂ thin films from nanoparticles by solvothermal method and selenisation process

Cu(In,Ga)Se₂ (CIGS) thin films were successfully synthesised by a facile and low-cost non-vacuum process. First, the chalcopyrite CIGS nanoparticles with nanoplate-like shapes were synthesised by a mild solvothermal method using CuCl₂·2H₂O, Ga₂Se₃, In₂Se₃ and elemental selenium as original materials. Secondly, homogeneous CIGS nanoinks were prepared and then spin-coated onto soda-lime glass substrates. Subsequently, CIGS precursor films were formed by two-step preheating treatments in air. Lastly, CIGS films were fabricated by selenisation process using Se vapour at 500-C. The obtained CIGS films were of a typical chalcopyrite structure and indicated p-type semiconductor characteristics. The optical bandgap of the films was 1.19-eV with a high-absorption coefficient exceeding 10⁴ cm^-1. The quality of the CIGS films was significantly improved by post-selenisation process.