Preparation of Cu(In,Ga)Se₂ nanoparticles via solvothermal method in conjunction with ball milling process and its applications to thin-film solar cells

Single-phase chalcopyrite CIGS particles with the sizes of 40–60 nm and the stoichiometry of Cu_26.01(In_17.00Ga_8.01)Se_48.98 were synthesized by the solvothermal method. The CIGS precursor layers were prepared via the doctor-blade coating process utilizing the slurry containing CIGS nanoparticles and the CIGS layers were then formed by a selenization at 540 °C for various times in the Se vapor ambient. Microstructure and composition analyses indicated the CIGS layers are of the singe-phase chalcopyrite phase and the Cu-poor composition feature with stoichiometry close to the ideal ratio of 1:1:2. Moreover, the increase of selenization time benefited the coarsening of grain structure in CIGS layer as revealed by the scanning electron microscopy. Accordingly, the CIGS thin-film solar cell samples with the Mo/CIGS/CdS/i-ZnO/AZO/Ag structure were prepared and their performance were evaluated. Under the AM1.5 illumination condition, the best PV performance with open-circuit voltage of 0.49 V, short-circuit current density of 29.46 mA/cm², fill factor of 54% and conversion efficiency of 7.75% was accomplished in the thin-film solar cell sample containing CIGS light absorption layer prepared by the 540°C-selenization for 15 min.