Re-Synthesis of CIGS Nanocrystallites Using Oxidation Roasting Pretreatment from Spent CIGS Targets

The CIGS (Cu(In, Ga)Se2) thin film solar cell sputtering process utilizes only 30% of the original target. The remaining 70% of the target must be recycled to achieve In, Ga, and Se rare metal sustainable use. It is, therefore, very important to establish spent CIGS target recycling technology to reduce environmental damage. CIGS is a tetrahedrally bonded semiconductor with a chalcopyrite crystal structure. Chalcopyrite is resistant to attack by the oxidants used in dissolution due to forming a passivation surface layer. Therefore, increasing the reaction temperature, lixiviating agent, and oxidant concentrations is necessary to enhance CIGS dissolution. The oxidation roasting pretreatment effects on the recovery and leaching of spent CIGS targets are investigated in this study. The results indicated that the proper oxidation roasting pretreatment process could significantly enhance CIGS leaching, reducing costs and increasing the reaction rate. This can be explained by the fact that the chalcopyrite structure was decomposed and transformed into easier dissolvable Cu2SeO4, In2O3, and amorphous Ga2O3 after roasting in the air. Cu, In, and Ga recoveries can reach above 99.9% by leaching CIGS roasted at 500 °C in 1 M H2SO4 at 60 °C for 1 h. As the roasting temperature was increased to 600 °C, the Ga recovery rate decreased due to the formation of difficult dissolvable β-Ga2O3. Mono-dispersed, near-stoichiometric CIGS nanoparticles with a mean crystallite size of 9 nm can be obtained using a direct recycling process combining oxidation, leaching, and re-synthesis processes.