Mylène Hendrickx

In this work, the effects of Si‐doping in Cu₂ZnSnS₄ are examined computationally and experimentally. The density functional theory calculations show that an increasing concentration of Si (from x = 0 to x = 1) yields a band gap rise due to shifting of the conduction band minimum towards higher energy states in the Cu₂Zn(Sn_1−xSi_x)S₄. CZTSiS thin film prepared by co‐sputtering process shows Cu₂Zn(Sn_1−xSi_x)S₄ (Si‐rich) and Cu₂ZnSnS₄ (S‐rich) kesterite phases on the surface and in the bulk of the sample, respectively. A significant change in surface electronic properties is observed in CZTSiS thin film. Si‐doping in CZTS inverts the band bending at grain‐boundaries from downward to upward and the Fermi level of CZTSiS shifts upward. Further, the coating of the CdS and ZnO layer improves the photocurrent to ≈5.57 mA cm⁻² at −0.41 V_RHE in the CZTSiS/CdS/ZnO sample, which is 2.39 times higher than that of pure CZTS. The flat band potential increases from CZTS ≈0.43 V_RHE to CZTSiS/CdS/ZnO ≈1.31 V_RHE indicating the faster carrier separation process at the electrode–electrolyte interface in the latter sample. CdS/ZnO layers over CZTSiS significantly reduce the charge transfer resistance at the semiconductor–electrolyte interface.