Numerical Optimization of Cd-Free CZTSe Kesterite Solar Cells with Tunable Zn(O,S) Buffer Layers Using Silvaco ATLAS
DOI:
https://doi.org/10.22399/ijcesen.5455Keywords:
CZTSe kesterite, Zn(O,S) buffer layer, Silvaco ATLAS, Cd-free solar cells, Device optimizationAbstract
Conventional Cu₂ZnSnSe₄ (CZTSe) kesterite solar cells commonly employ toxic CdS buffer layers that introduce parasitic blue-light absorption, cadmium-related environmental hazards, and potentially unfavorable conduction-band offsets (CBOs) that contribute to the open-circuit-voltage deficit. This study numerically optimizes a fully Cd-free glass/Mo/p-CZTSe/n-Zn(OₓS₁₋ₓ)/n-ZnO/ITO architecture using Silvaco ATLAS TCAD. The model solves the self-consistent Poisson, drift-diffusion, and carrier-continuity equations with Shockley-Read-Hall (SRH), radiative, and Auger recombination under AM1.5G illumination (100 mW cm⁻², 300 K). A compositional sweep of Zn(OₓS₁₋ₓ) (x = 0 to 1) identifies Zn(O₀.₄S₀.₆) as the optimum buffer, yielding η = 12.79%, Jsc = 39.47 mA cm⁻², Voc = 461.66 mV, and FF = 70.24% for the baseline dimensions. Subsequent optimization of the CZTSe thickness (4 µm), Zn(O,S) thickness (0.05 µm), ZnO thickness (0.06 µm), and CZTSe acceptor density (NA = 1.4 × 10¹⁵ cm⁻³) increases the simulated performance to η = 14.13%, Jsc = 41.20 mA cm⁻², Voc = 483.08 mV, and FF = 71.02%. Simulations from 240 to 350 K show monotonic degradation of Voc and η with temperature, consistent with SRH-dominated bulk recombination. The results provide a physically grounded, simulation-guided basis for Cd-free CZTSe device engineering and require experimental validation.
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