.Effect of calcium substitutional doping on the structural and optical properties of kesterite Cu2ZnSnS4 thin films

CZTS (Cu2ZnSnS4) kesterite-based solar cells represent promising low-cost and eco-friendly alternatives to traditional solar technologies. While CZTS absorber layers exhibit notable optical advantages, their solar cell efficiency remains below 15 %. One strategy to enhance the optical performance of these layers is doping with alkaline earth metals. This study systematically investigates the calcium incorporation in CZTS thin films synthesized via the cost-effective spray pyrolysis technique. In this study, an attempt has been made to investigate the optical behavior of CZTS layers doped with 1 % to 4 % by weight of calcium. Thin CZTS layers were initially deposited onto the SLG surface using pneumatic spray pyrolysis, followed by annealing in a sulfur vapor and argon atmosphere. The deposited thin films were subsequently characterized by XRD, AFM, FESEM, EDX, DRS, FTIR, and Raman spectroscopy techniques. The results indicate that increasing calcium doping up to 4 % enhances the effective absorption of CZTS thin films in the visible spectrum. Additionally, calcium doping reduces the band gap of the CZTS absorber, reaching 1.41 eV at a 4 % Ca concentration. The increase in optical conductivity with higher Ca doping suggests that calcium improves the optical response of CZTS thin films. Structural analysis confirms that the thin films are well-formed in the kesterite structure. Surface morphology analysis indicates that as calcium doping increases, surface roughness also rises. This increase in roughness could enhance photon absorption but may adversely affect the interface between the absorber and buffer layers.