First-principles comparative investigation of band-gap engineering in BaZrS3 via Ti, Sn, Ca, Sr, and Se doping

Abstract

BaZrS₃ is a promising absorber material for photovoltaic applications owing to its direct band gap, high absorption coefficient and excellent thermal and chemical stability. However, a comprehensive and consistent comparative assessment of Ti, Sn, Ca, Sr and Se doping effects using a unified computational framework is still needed. In this work, we systematically investigate the structural, electronic and optical properties together with formation energies and charge-density characteristics of Ti, Sn, Ca, Sr and Se doped BaZrS₃ using first-principles density functional theory (DFT) calculations within the \(DFT+U\) formalism. Doping is introduced by substituting Ba with Ca or Sr, Zr with Ti or Sn at a concentration of \(25\,\%\) and S with Se at a concentration of \(8.3\,\%\) within the unit cell. Structural analysis reveals dopant dependent lattice expansion or contraction accompanied by local structural distortions. The calculated formation energies provide insight into the relative stability and feasibility of dopant incorporation within the \(\hbox {BaZrS}_3\) lattice. By comparing aliovalent and isovalent substitutions at different crystallographic sites, we identify a clear orbital-selective band-edge control mechanism in BaZrS₃, wherein Zr-site dopants govern the conduction band minimum, anion substitution modulates the valence band maximum and Ba-site substitutions remain electronically inert. Optical property analysis indicates that Ti and Sn doped systems exhibit a redshift in the absorption onset with enhanced visible light absorption compared to other dopants. Furthermore, charge density analysis at the valence band maximum and conduction band minimum elucidates the orbital contributions and bonding characteristics in both pristine and doped BaZrS₃. Overall, this study identifies Ti, Sn and Se doping as particularly promising strategies for tuning BaZrS₃ towards an optimal band gap range for photovoltaic applications.