A cooler tin selenide: Thermoelectric materials can convert heat into electricity or be used as the basis of cooling devices. Qin et al . found that doping a tin selenide thermoelectric material with lead and sodium improved the room temperature thermoelectric properties, an effect created by manipulation of the electronic bands. The authors showed that the material could be used not only for power generation but also cooling. If optimal contact materials are identified, then this approach may be attractive for future applications. —BG

Thermoelectric technology has been widely used for key areas, including waste-heat recovery and solid-state cooling. We discovered tin selenide (SnSe) crystals with potential power generation and Peltier cooling performance. The extensive off-stoichiometric defects have a larger impact on the transport properties of SnSe, which motivated us to develop a lattice plainification strategy for defects engineering. We demonstrated that Cu can fill Sn vacancies to weaken defects scattering and boost carrier mobility, facilitating a power factor exceeding ~100 microwatts per centimeter per square kelvin and a dimensionless figure of merit ( ZT ) of ~1.5 at 300 kelvin, with an average ZT of ~2.2 at 300 to 773 kelvin. We further realized a single-leg efficiency of ~12.2% under a temperature difference (Δ T ) of ~300 kelvin and a seven-pair Peltier cooling Δ T _max of ~61.2 kelvin at ambient temperature. Our observations are important for practical applications of SnSe crystals in power generation as well as electronic cooling.

Thermoelectric materials allow for direct conversion between heat and electricity, offering the potential for power generation. The average dimensionless figure of merit ZT _ave determines device efficiency. N-type tin selenide crystals exhibit outstanding three-dimensional charge and two-dimensional phonon transport along the out-of-plane direction, contributing to a high maximum figure of merit Z _max of ~3.6 × 10 ⁻³ per kelvin but a moderate ZT _ave of ~1.1. We found an attractive high Z _max of ~4.1 × 10 ⁻³ per kelvin at 748 kelvin and a ZT _ave of ~1.7 at 300 to 773 kelvin in chlorine-doped and lead-alloyed tin selenide crystals by phonon-electron decoupling. The chlorine-induced low deformation potential improved the carrier mobility. The lead-induced mass and strain fluctuations reduced the lattice thermal conductivity. Phonon-electron decoupling plays a critical role to achieve high-performance thermoelectrics.

Thermoelectric cooling technology has important applications for processes such as precise temperature control in intelligent electronics. The bismuth telluride (Bi ₂ Te ₃ )–based coolers currently in use are limited by the scarcity of Te and less-than-ideal cooling capability. We demonstrate how removing lattice vacancies through a grid-design strategy switched PbSe from being useful as a medium-temperature power generator to a thermoelectric cooler. At room temperature, the seven-pair device based on n-type PbSe and p-type SnSe produced a maximum cooling temperature difference of ~73 kelvin, with a single-leg power generation efficiency approaching 11.2%. We attribute our results to a power factor of >52 microwatts per centimeter per square kelvin, which was achieved by boosting carrier mobility. Our demonstration suggests a path for commercial applications of thermoelectric cooling based on Earth-abundant Te-free selenide-based compounds.

Thermoelectrics have been limited by the scarcity of their constituent elements, especially telluride. The earth-abundant, wide-bandgap ( E _g ≈ 46 k _B T ) tin sulfide (SnS) has shown promising performance in its crystal form. We improved the thermoelectric efficiency in SnS crystals by promoting the convergence of energy and momentum of four valance bands, termed quadruple-band synglisis. We introduced more Sn vacancies to activate quadruple-band synglisis and facilitate carrier transport by inducing SnS ₂ in selenium (Se)–alloyed SnS, leading to a high dimensionless figure of merit ( ZT ) of ~1.0 at 300 kelvin and an average ZT of ~1.3 at 300 to 773 kelvin in p-type SnS crystals. We further obtained an experimental efficiency of ~6.5%, and our fabricated cooler demonstrated a maximum cooling temperature difference of ~48.4 kelvin at 353 kelvin. Our observations should draw interest to earth-abundant SnS crystals for applications of waste-heat recovery and thermoelectric cooling.

Thermoelectric technology experienced rapid development over the past 20 years, with the most promising applications being in both power generation and active cooling. Among existing thermoelectrics, tin selenide (SnSe) has had particularly rapid development owing to the unexpectedly high thermoelectric efficiency that has been continuously established over the past decade. Several transport mechanisms and strategies used to interpret and improve the thermoelectric performance of SnSe have been important for understanding and developing other material systems with SnSe-like characteristics. Similar to other thermoelectrics, building commercially viable SnSe-based devices requires advances in device efficiency and service stability. Further optimization across all material systems should enable thermoelectric technology to play a critical role in the future global energy landscape.