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.