Device-level photovoltaic assessment of lead-free X2SnCl6 (X = K, Rb) perovskites: Ab-initio study

초록

Although lead-based halide perovskites have demonstrated high power conversion efficiencies in solar cells, their toxicity and limited stability under ambient conditions remain major obstacles to commercialization. To overcome these challenges, the lead-free double perovskites K2SnCl6 and Rb2SnCl6 were investigated in the present work as promising eco-friendly alternatives. Density functional theory was employed to investigate the structural, electronic, optical, mechanical, thermodynamic, and thermoelectric properties of the lead-free double perovskites K2SnCl6 and Rb2SnCl6, and these results were validated by device-level photovoltaic simulations using J-V and EQE measurements. Stability was assessed using tolerance factors, phonon behavior, and formation enthalpies, supporting the compounds' thermodynamic and kinetic stability. Using the HSE-06 hybrid functional, direct band gaps of 2.64 eV for K2SnCl6 and 2.31 eV for Rb2SnCl6 were obtained, confirming their semiconducting features. The mechanical evaluation indicates that K2SnCl6 is brittle, whereas Rb2SnCl6 is ductile, and both exhibit primarily ionic bonding. Optical analyses reveal significant absorption within the visible spectrum and minimal reflectivity, implying potential for solar applications. Simulations at the device level-specifically, J-V characteristics and EQE performance-were conducted to study photovoltaic behavior. The systems exhibit high short-circuit current densities and strong photo-response at around 330 nm, indicating effective photogeneration. The SLME model estimated power conversion efficiencies of 13.21 % for K2SnCl6 and 9.53 % for Rb2SnCl6. The calculated moderate effective masses (me* approximate to 0.38-0.45 m0, mh* approximate to 0.51-0.74 m0) and reasonable electron mobilities further corroborate the potential of these lead-free double perovskites for efficient charge extraction in photovoltaic devices.

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