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چکیده
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This study investigates the photovoltaic behavior of cascaded solar cells composed of CsSnBr3 and Cs3Bi2I9 absorbers, focusing on band alignment, carrier dynamics, and environmental stability. Single-absorber devices were first optimized individually: the Cs3Bi2I9-based cell achieved a peak efficiency of 14.23% at an optimal thickness of 700 nm with acceptor density NA = 1.0 × 109 cm−3, while the CsSnBr3-based cell reached 19.03% at 600 nm with NA = 1.0 × 1015 cm−3, both under low defect density (Nt = 1.0 × 1015 cm−3). The cascaded configuration combining CsSnBr3 (600 nm) and Cs3Bi2I9 (700 nm) demonstrates enhanced carrier extraction, favorable band alignment, and a higher built-in potential (Vbi = 1.12 V). Mott–Schottky analysis verifies the stability of the depletion region and highlights the importance of absorber thickness optimization. Carrier generation–recombination profiles reveal that the cascaded device redistributes generation across both absorbers while progressively suppressing recombination toward the back interface, thereby improving efficiency. Electron and hole concentration analysis further validates effective charge separation and selective transport through TiO2 and PEDOT:PSS layers. Under clear-sky AM 1.5G illumination, the cascaded device reaches a power conversion efficiency of 28.24%. Simulations under cloudy conditions (30–70% irradiance reduction) show that while Voc and fill factor remain stable, short-circuit current density (Jsc) declines significantly, driving efficiency losses. These results emphasize the dual advantage of cascaded absorbers: broad spectral absorption and reduced recombination losses, while also highlighting their sensitivity to spectral shifts under diffuse illumination. The findings provide insights into optimizing cascaded solar cells for real-world conditions and suggest pathways for mitigating performance degradation under variable irradiance.
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