First-principles study of structural, mechanical, optoelectronic and thermoelectric properties of lead-free Cs₂BSnX₆ (B = Mg, Cu; X = Cl, Br, I) for photo responsive RRAM devices

Currently, halide perovskites with exceptional properties are the most suitable candidates for RRAM devices. In the present study, a comprehensive investigation of structural, mechanical, optoelectronic and thermoelectric properties of Cs₂BSnX₆ (B = Mg, Cu; X = Cl, Br, I) has been conducted for the potential application in resistive switching random access memory (RRAM) devices. Mechanical properties display that studied perovskites exhibit mechanical stability and ductile behavior with an anisotropic character. A comparison of band structure using PBE-GGA, and TB-mBJ was also made. The band structure with TB-mBJ investigation disclosed that Cs₂MgSnCl₆, Cs₂MgSnBr₆, Cs₂MgSnI₆, Cs₂CuSnCl₆, Cs₂CuSnBr₆, and Cs₂CuSnI₆ have indirect bandgaps with value of 3.64 eV, 2.87 eV, 2.05 eV, 2.30 eV, 1.50 eV and 0.90 eV respectively. These values are found to be slightly more than PBE-GGA approximations. The optical investigation illustrates that Cs₂CuSnI₆ can absorb a wide range of electromagnetic radiation wavelengths from ultraviolet to infrared, making it the optimal candidate for RRAM devices. Thermoelectric properties show electrical conductivity values of the 1.65 × 10¹⁹, 1.61 × 10¹⁹, 1.58 × 10¹⁹, 1.95 × 10¹⁹, 2.35 × 10¹⁹, 2.40 × 10¹⁹ (Ω.m.s)⁻¹ for Cs₂MgSnCl₆, Cs₂MgSnBr₆, Cs₂MgSnI₆, Cs₂CuSnCl₆, Cs₂CuSnBr₆, and Cs₂CuSnI₆ respectively at 1500 K. Furthermore, the calculated optical and thermoelectric properties of Cs₂BSnX₆ (B = Mg, Cu; X = Cl, Br, I) compared with previously studied Cs₂CaSnX₆ (X = Cl, Br, I), disclosing that Mg and Cu-based perovskites display better optical and thermoelectric properties. The vital findings of this study express that Cs₂CuSnI₆ is the most appropriate candidate for less-energy consuming RRAM devices among all studied perovskites.