Electrodeposition of Cu₂FeSnS₄ thin films for solar cell applications: mechanism of deposition and influence of Fe²⁺ concentration

In this study, we successfully synthesized semiconductor thin films of Cu₂FeSnS₄ (CFTS) using the electrodeposition method. We delved into the mechanisms of electrochemical nucleation and growth, shedding light on these processes. Utilizing potentiostatic current-density-time transient measurements and in situ electrochemical impedance spectroscopy (EIS), we explored the nucleation and growth mechanisms of Cu₂FeSnS₄ (CFTS) thin films, deposited from an aqueous solution under various applied potentials. Cyclic voltammetry was employed to investigate the electrochemical behaviors of Cu-Fe-Sn-S precursors in a trisodium citrate medium. Chronoamperometry and EIS analysis were conducted to delve deeply into the deposition mechanism and surface electrode-electrolyte phenomena. Furthermore, the study explored the impact of Fe²⁺ concentration on structural morphology and optical properties. X-ray diffraction and Raman analysis unveiled the stannite structure within the obtained Cu₂FeSnS₄ thin film, alongside the presence of secondary phases in the CFTS elaborated at both lower and higher concentrations of Fe²⁺. SEM images reveal that the sulfurized CFTS C2 (0.01 M of Fe²⁺) sample has a surface morphology with irregular particles. EDS mapping and EDX analysis confirm that the elemental concentrations of Cu, Fe, Sn, and S in the CFTS C2 thin films closely match the desired stoichiometry for Cu₂FeSnS₄. UV-visible spectroscopy revealed a suitable bandgap energy within the range of 1.5 eV for the film deposited with a Fe²⁺ concentration of 0.01 M.