Co-electrodeposition of CZT precursor for Cu2ZnSnS4 thin film absorber layer.

In this study, co-electrodeposition was used to fabricate CuZnSn precursor, and followed by preheating and sulfurization to synthesize CuvZnSnSi absorber layer. The co-deposition potential E = -1.25 V was determined by cyclic voltammetry (CV). The effects of pH and electrolyte concentration on the composition and phases of the metal precursor were investigated. By optimization of the parameters, a CZT film with composition close to n ( Cu )/n (Zn + Sn ) ≈ 0.8, n (Zn)/n (Sn) ≈ 1.2 was deposited from an aqueous solution containing 8 mmol/L SnSO₄ 22 mmol/L CuSO₄ ⋅ 5H₂O, 22 mmol/L ZnSO₄ ⋅ 7H₂O, and 200 mmol/L Na₃C₆H₅O₇ ⋅ 2H₂O with pH = 5. 7. After preheating at 300 °C, the metal precursor transformed into a solid solution of Cu₅Zn₈ and Cu₆Sn₅ alloys, which established the foundation for a pure CZTS formation. During sulfurization, annealing time and temperature had a significant impact on the structure and morphology of the film. With the increase in annealing time, the intensity of the characteristic peak of CZTS increased, the intensity of impurity phase peaks (Cu_2-xS, SnS and Cu₂Sn₃) decreased, and CZTS was purified gradually. When the sulfurization time was up to 60 min, the film had a good structure and morphology? but the film was easy to decompose with longer annealing. Too low sulfurization temperature would lead to binary and ternary phases in the film? while too high temperature would result in the loss of Sn and Zn. When sulfurization temperature was 580 °C, the CZTS film had obvious grain profile and distinct grain boundaries, and was dense and uniform (around 2 µm thickness) with less voids and good adhesion to the Mo layer. [ABSTRACT FROM AUTHOR]