Impact of B-site Cation Transmutation in Halide Perovskites CsXBr3 (X = Pb, Sn)

The substitution of lead (Pb) with tin (Sn) at the B-site of halide perovskites offers a compelling approach toward the development of non-toxic, environmentally sustainable optoelectronic materials. In this work, first-principles Density Functional Theory (DFT) calculations are used to examine the structural, electronic, and optical characteristics of CsPbBr3 and CsSnBr3. Structural optimization reveals that both materials stabilize in a cubic $$Pm\bar {3}m$$ (#221) symmetry with a tolerance factor of 0.83 and 0.88, underscoring their structural robustness. Remarkably, substituting Pb with Sn leads to a significant reduction in the band gap, from 2.80 eV in CsPbBr3 to 1.42 eV in CsSnBr3 (calculated using the TB-mBJ method), transitioning these materials toward better suitability for visible-light absorption. The optical properties reveals that CsSnBr3 exhibits a higher static dielectric constant and refractive index than CsPbBr3, with comparable absorption onset near 0.63 eV. These results reveal the CsSnBr3 potential for effective optoelectronic applications by providing increased light-matter interaction and enhanced dielectric screening. In this study, the role of B-site cation substitution in tuning key material properties, this work provides critical insights for the design of lead-free, sustainable perovskites, offering a promising pathway toward environmentally friendly technologies that address the growing demand for clean energy.