Enhancing the thermoelectric performance of n-type polycrystalline SnSe with lead-free perovskite Cs2TiCl6

Abstract

Enhancing the thermoelectric performance of n-type polycrystalline SnSe remains challenging due to the trade-off between carrier transport and lattice thermal conductivity. Here, we demonstrate that trace incorporation of the lead-free perovskite Cs₂TiCl₆ enables concurrent optimization of these factors in SnSe_0.93. The [TiCl₆]²⁻ octahedral framework introduces effective electron donors, while Ti 3d states induce local band flattening, increasing the density-of-states effective mass without severely degrading weighted mobility. Consequently, the 0.5 wt% Cs₂TiCl₆ sample attains a high power factor of ∼532.1 µW m⁻¹ K⁻² at 823 K. Meanwhile, Ti-rich domains together with multi-scale structural defects (strain fields, dislocations, and twin boundaries) substantially intensify phonon scattering, driving the lattice thermal conductivity down to ∼0.32 W m⁻¹ K⁻¹ at 823 K—a 40.6% reduction relative to the pristine specimen. Benefiting from this synergistic carrier and phonon engineering, a peak ZT of ∼1.2 at 823 K is achieved for 0.5 wt% Cs₂TiCl₆, representing a 179.1% enhancement over undoped SnSe_0.93 and outperforming most reported n-type polycrystalline SnSe-based materials. This work establishes trace lead-free perovskite doping as a dual-function strategy—simultaneously enabling band structure modulation and phonon mean free path suppression—offering a viable route toward environmentally benign, high-efficiency n-type SnSe thermoelectrics.