Effect of Annealing Time and Heat Flux on Solvothermal Synthesis of CIGS Nanoparticles

CuInxGa(1-x)Se2 (CIGS) is a renowned absorbing material in solar cell application due to its wide and tunable direct bandgap with high absorption coefficient. The highest efficiency achieved on lab scale device is 22.6% which is competitive to Si based solar cells. CIGS nanoparticles are prominent materials for solar photovoltaic applications due to its high surface to volume ratio and for its use in relatively low processing temperature. In the study, CIGS nanoparticles are synthesized using modified solvothermal method in which the size and agglomeration of CIGS nanoparticles are controlled by introducing ammonium halides. The formation mechanism of CIGS nanoparticles while heating at 230 °C in hot air oven and in muffle furnace for various time durations are studied and analysed in detailed. The crystal phase and crystallite size are evaluated using X-ray diffraction and the phase is confirmed by Raman spectroscopy. The synthesized CIGS nanoparticles from 5 hours and 7 hours of reaction time exhibited tetragonal chalcopyrite crystal structure with an average crystallite size of 41 nm in hot air oven and 125 nm in furnace. The optical band gap of the CIGS nanoparticles measured by UV-Vis-NIR spectroscopy is found to be 1.52 eV for 5 hours and 1.56 eV for 7 hours of reaction time in both oven and furnace prepared samples, that indicates the quality of material is high and could be used for photovoltaic device fabrication