The Study Of Electrodeposition Cu（In,Ga）Se₂Thin Films From Ionic Liquid Electrolytes

Solar cells is a clean, renewable energy, so it has attracted much attention. CIGS thin film solar cells with its high conversion efficiency, strong radiation resistance, low production cost and good stability have become the research focus of the international PV industry. CIGS is a promising absorbing layer for thin film solar cells with a high optical absorption coefficient (1×105cm-1) and adjustable band gap(1.05～1.67eV) etc. In order to get high-quality CIGS thin films as well as increase the Ga content, researchers start to use ionic liquid to replace aqueous solution. In order to develop a roll-to-roll industrial process, researchers began to use metal and polymer etc. flexible substrates to replace the traditional Mo/glass substrate. In this paper, one-pot electrodeposition CIGS thin films in ionic liquid on Ni substrate was studied to explore high-quality CIGS thin films preparation process and lay the foundation for the large area, low-cost preparation of CIGS thin film solar cells.In this paper, electrodeposition In, Ga, Cu-In, Cu-In-Ga, Cu-In-Se and Cu-In-Ga-Se was studied using ionic liquid as solvent, and CuCl2、InCl3GaCl3、H2SeO3as main salts. Many methods has been tried to increase the Se content. The results showed that using SeCl4instead of H2SeO3as selenium source could increase the Se content in the CIGS thin films.Then the reproducibility of CIGS thin films composition was studied. The results showed that the reproducibility could be improved by increasing bath’s size, bath temperature and adding agitator.Then, we studied the influences of the bath temperature, deposition potential and bath composition etc parameters on the composition of the CIGS thin films. Stoichiometric CIGS thin films have been obtained under the solution composition of7.5mol/L CuCl2,35mmol/L InCl3,30mmol/L GaCl3and70mmol/L SeCl4. The content of In and Se increased and the CIGS thin film morphology improved with the increase of the bath temperature. The content of In and Ga increased and the CIGS thin film morphology improved with the negative shift of the deposition potential. The effects of the annealing process on the coating surface morphology, composition and structure were also studied. Annealing process could eliminate impurity phases and improve crystallinity of the coating. In the other hand, Ga content decreased after annealing process and chalcopyrite CIGS thin films could not be obtained. The deposition behavior of the unitary CuCl2、InCl3、GaCl3、SeCl4systems, binary CuCl2+SeCl4, InCl3+SeCl4, GaCl3+SeCl4systems, ternary CuCl2+InCl3+SeCl4system and quaternary CuCl2+InCl3+GaCl3+SeCl4system were studied by cyclic voltammetry. The results indicated that in binary systems, the deposition of Cu-Se fitted with kroger’s mechanism, the deposition of In3+and Ga3+proceeded by underpotential deposition. In the ternary system, the insertion of In into the CIS thin films involved two routes:co-deposition with Cu2+and Se or direct reduction into In. In the quaternary system, the insertion of Ga into the CIGS thin film had two routes too:co-deposition with Cu2+, In3+and Se or direct reduction into Ga, and Ga3+direct reduction to Ga was a surface-induce deposition process.