Investigation of Optimum Conditions for Synthesis of Cu(In,Ga)Se₂ Nanoparticles by Refluxing

Cu(In,Ga)Se₂ (CIGSe) has been proven to be a better candidate as a light absorber layer in thin-film solar cells. However, most processes require high vacuum and high temperature during deposition, which results in significant loss of materials and is not applicable to a flexible substrate. Solution processes often involve low processing temperature and cheap precursor, can be used with flexible substrates, and offer the possibility of roll-to-roll manufacturing, potentially reducing manufacturing costs for the module. Here, we have experimentally investigated the optimum synthesis conditions for CIGSe nanoparticles fabricated by using a facile and a non-vacuum reflux method for low-temperature solution processes. By employing various reflux conditions by changing the temperature of heating mantle, single-phase CIGSe nanoparticles were synthesized at 200 °C. On the other hand, synthesized products with an impure multi-phase were formed at heating mantle temperatures lower than 200°C. XRD measurements confirmed that the Ga content of the CIGSe nanoparticles increased with increasing heating mantle temperature. In addition, the average diameter of the CIGSe nanoparticles increased with increasing reaction time from 5 min to 30 min at a fixed heating mantle temperature of a 200 °C. The optical band gap is calculated by using ultraviolet-visible (UV-Vis) absorption spectra, decreased from 1.69 eV to 1.29 eV with increasing reaction time due to the increased CIGSe nanoparticles size. From our results, we can conclude that the characteristics of the CIGSe nanoparticles can be effectively controlled by using simple growth conditions, thereby providing many advantages for the fabrication of absorber layers for use in CIGSe solar cells.