Lead-free double perovskite halides Cs₂TiCl₆ and Cs₂ZrCl₆: A first-principles study for wide-bandgap optoelectronic applications
Energy Reports, cilt.16, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 16
- Basım Tarihi: 2026
- Doi Numarası: 10.1016/j.egyr.2026.109638
- Dergi Adı: Energy Reports
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Compendex, INSPEC, Directory of Open Access Journals
- Anahtar Kelimeler: Double perovskites, Electronic structure, Mechanical stability, Mineral processing, Optical properties, Thermoelectric properties
- Recep Tayyip Erdoğan Üniversitesi Adresli: Evet
Özet
Double perovskite halides are gaining attention as promising materials for next-generation optoelectronic and thermoelectric technologies due to their tunable electronic properties and structural stability. In this first-principles investigation, we explore the structural, dynamical, electronic, mechanical, optical, and thermoelectric characteristics of Cs₂TiCl₆ and Cs₂ZrCl₆ using density functional theory (DFT). Phonon dispersion analysis confirms dynamical stability, with both compounds showing no imaginary frequencies across the Brillouin zone. The optimized lattice parameters are 10.4576 Å for Cs₂TiCl₆ and 10.6251 Å for Cs₂ZrCl₆, reflecting lattice expansion upon Ti→Zr substitution. Electronic structure calculations indicate direct band gaps of 2.185 eV (GGA) and 2.913 eV (mBJ-GGA) for Cs₂TiCl₆, and wider gaps of 3.642 eV and 4.419 eV for Cs₂ZrCl₆. Density-of-states analysis shows that the valence-band edge is mainly derived from Cl-3p states, whereas the conduction-band edge is dominated by Ti-3d or Zr-4d states. Mechanical analysis confirms elastic stability with bulk moduli of 31.13 GPa and 35.89 GPa, respectively. Both compounds exhibit moderate refractive indices and appreciable absorption above their respective band-gap energies. Cs₂TiCl₆ responds near the visible–UV boundary, whereas Cs₂ZrCl₆ is primarily active in the UV region, indicating possible relevance to UV-sensitive optoelectronic and wide-band-gap photonic applications. From a broader materials-production perspective, the synthesis of Cs₂TiCl₆ and Cs₂ZrCl₆ may involve precursor elements obtained from ores through mineral processing and beneficiation routes. Thermoelectric calculations yield positive Seebeck coefficients of approximately 200 μV/K for Cs₂TiCl₆ and 300 μV/K for Cs₂ZrCl₆ at 300 K. Because the transport calculations employ the constant relaxation time approximation and do not independently include the lattice thermal conductivity, these results are interpreted mainly as comparative transport trends rather than absolute predictions of thermoelectric efficiency. The relatively large band gaps indicate that these materials are more suitable for UV optoelectronic and wide-band-gap photonic applications rather than conventional single-junction photovoltaic absorbers.