Flexibility potential of Cs2BX6 (B=Hf, Sn, Pt, Zr, Ti; X=I, Br, Cl) with application in photovoltaic devices and radiation detectors

As interest in double perovskites is growing, especially in applications like photovoltaic devices, understanding their mechanical properties is vital for device durability. Despite extensive exploration of structure and optical properties, research on mechanical aspects is limited. This article builds a vacancy-ordered double perovskite model, employing first-principles calculations to analyze mechanical, bonding, electronic, and optical properties. Results show Cs2HfI6, Cs2SnBr6, Cs2SnI6, and Cs2PtBr6 have Young's moduli below 13 GPa, indicating flexibility. Geometric parameters explain flexibility variations with the changes of B and X site composition. Bonding characteristic exploration reveals the influence of B and X site electronegativity on mechanical strength. Cs2SnBr6 and Cs2PtBr6 are suitable for solar cells, while Cs2HfI6 and Cs2TiCl6 show potential for semi-transparent solar cells. Optical property calculations highlight the high light absorption coefficients of up to 3.5×105 cm−1 for Cs2HfI6 and Cs2TiCl6. Solar cell simulation shows Cs2PtBr6 achieves 22.4% of conversion efficiency. Cs2ZrCl6 holds promise for ionizing radiation detection with its 3.68 eV bandgap and high absorption coefficient. Vacancy-ordered double perovskites offer superior flexibility, providing valuable insights for designing stable and flexible devices. This understanding enhances the development of functional devices based on these perovskites, especially for applications requiring high stability and flexibility.