Electrodeposition Process and Performance of CuIn(Se _x S_1−x )₂ Film for Absorption Layer of Thin-Film Solar Cells

CuIn(Se _x S_1−x )₂ thin film is prepared by the electrodeposition method for the absorption layer of the solar cell. The CuIn(Se _x S_1−x )₂ films are characterized by cyclic voltammetry measurement for the reduction of copper, indium, selenium and sulfur in selenium and sulfur in aqueous solutions with sodium citrate and without sodium citrate. In the four cases, the defined reduction process for every single element is obtained and it is observed that sodium citrate changes the reduction potentials. A linear relationship between the current density of the reduction peak and (scan rate v)^1/2 for copper and indium is achieved, indicating that the process is diffusion controlled. The diffusion coefficients of copper and indium ions are calculated. The diffusional coefficient D value of copper is higher than that of indium, and this is the reason why the deposition rate of copper is higher. When four elements are co-deposited in the aqueous solution with sodium citrate, the quaternary compound of CuIn(Se _x S_1−x )₂ is deposited together with Cu₃Se₂ impure phases after annealing, as found by XRD spectra. Morphology is observed by SEM and AFM. The chemical state of the films components is analyzed by XPS. The UV-Visible spectrophotometer and electrochemistry workstation are employed to measure the photoelectric properties. The results show that the smooth, uniform and compact CuIn(Se _x S_1−x )₂ film is a semiconductor with a band gap of 1.49 eV and a photovoltaic conversion efficiency of 0.45%.