High thermoelectric performance in Bi2Se2S compounds via multi-element doping using a double-halide perovskite

Abstract

The optimization of the thermoelectric transport properties of materials necessitates high solubility of multiple dopant elements. This study implements a “multi-element doping” strategy in Bi₂Se₂S-based thermoelectric materials wherein the double-halide perovskite Cs₃Bi₂I₆Cl₃ is employed as a multifunctional dopant source, enabling the effective co-doping of Cl, I, Bi and Cs elements into the Bi₂Se₂S lattice. This strategy significantly increases the carrier concentration of Bi₂Se₂S to 14.86 × 10¹⁹ cm⁻³ and achieves an electrical conductivity of 395 S cm⁻¹ in the Bi₂Se₂S-1.00 wt% Cs₃Bi₂I₆Cl₃ sample at 323 K. Meanwhile, multi-scale structural defects induced by multi-element doping synergistically form a full-spectrum phonon scattering network, significantly suppressing lattice thermal conductivity across the full temperature spectrum. Furthermore, the defect formation energy calculations further confirmed that Cl, I, Bi and Cs are readily incorporated into the host lattice, forming solid solutions. Consequently, the lattice thermal conductivity for the 1.00 wt% Cs₃Bi₂I₆Cl₃ doped sample is reduced to 0.30 W m⁻¹ K⁻¹ at 773 K. Thus, the Bi₂Se₂S sample with 1.00 wt% Cs₃Bi₂I₆Cl₃ exhibits a peak ZT of 0.90 and an average ZT value of 0.55 across the temperature range of 323–773 K. Overall, this work establishes that the multi-element doping strategy effectively circumvents the solubility limits of single dopants, striking a balance between carrier concentration optimization and multi-scale phonon scattering to maximize thermoelectric performance.