Realizing High‐Ranged Out‐of‐Plane ZTs in N‐Type SnSe Crystals through Promoting Continuous Phase Transition

Abstract

Thermoelectric technology enables direct conversion between heat and electricity. The conversion efficiency of a thermoelectric device is determined by the average dimensionless figure of merit ZTave. Here, a record high ZTave of ≈1.34 in the range of 300–723 K in n‐type SnSe based crystals is reported. The remarkable thermoelectric performance derives from the high power factor and the reduced thermal conductivity in the whole temperature range. The high power factor is realized by promoting the continuous phase transition in SnSe crystals through alloying PbSe, which results in a higher symmetry of the crystal structure and the correspondingly modified electronic band structure. Moreover, PbSe alloying induces mass and strain fluctuations, which enables the suppression of thermal transport. These findings provide a new strategy to enhance the thermoelectric performance for the continuous phase transition materials.

Slowing down the heat in thermoelectrics

“…Specifically, for SnSe–PbSe crystals along the out‐of‐plane direction, κ lat at 300 K was depressed from ~0.8 to ~0.5 Wm −1 K −1 , and κ lat approached the theoretically minimum value ( κ lat,min ) of ~0.18 Wm −1 K −1 . This reduction was apparent, particularly near room temperature (300 K), which was further quantitatively estimated by the Debye–Callaway model 166,174 . The experimental κ lat at 300 K fitted well with the simulated line, and the inset shows the quantitative contributions of Γ M and Γ S to the reduction of κ lat (Figure 3(C)).…”

“…Atomic substitution caused by doping or alloying is the simplest and most common source of point defects and has been proven to be an effective approach to reduce κ lat in various thermoelectric systems 56,166–172 . Figure 3(A) depicts a typical image of n‐type SnSe crystals alloyed with 12% PbSe, in which the positions of Sn/Pb and Se are marked, and the positions of Pb were further confirmed and clarified by electron energy loss spectroscopy 166 . This Sn/Pb substitution leads to a significant decrease in κ lat (Figure 3(B)).…”

“…(A) A typical high‐angle annular dark field‐scanning transmission electron microscopy (HAADF–STEM) image for an n‐type SnSe‐12PbSe crystal along the (001) direction. Reproduced with permission from Reference 166. Copyright 2019, Wiley‐VCH.…”

High‐Performance Thermoelectric SnSe: Aqueous Synthesis, Innovations, and Challenges

“…A summary of ZTs for SnSe‐based thermoelectric materials. a) The timeline for state‐of‐the‐art SnSe bulks thermoelectric materials,11–124,169–182 the performance achieved by solution route are circled by yellow. b) Temperature‐dependent ZT and c) corresponding peak and average ZT values for polycrystalline SnSe through different fabrication techniques 13,16,22,46,58,62,95,99,101.…”

Realizing zT Values of 2.0 in Cubic GeTe

“…In the past couple of decades, much attention has been focused on prominent medium‐temperature materials such as PbTe and SnSe. Through multi‐pronged physics and careful materials processing, these materials have been reported to reach zT above 2 at 700–900 K [25–33] . Another class of prominent medium‐temperature thermoelectric materials that has found some commercial adoptions is TAGS (Te−Ag‐Ge−Sb) compounds (which are the alloys of GeTe‐AgSbTe2) [34] .…”