Defect Engineering Boosted Ultrahigh Thermoelectric Power Conversion Efficiency in Polycrystalline SnSe

Br doping-induced evolution of the electronic band structure in dimorphic and hexagonal SnSe2 thermoelectric materials

SnSe2 with its layered structure is a promising thermoelectric material with intrinsically low lattice thermal conductivity. However, its poor electronic transport properties have motivated extensive doping studies. Br doping effectively improves the power factor and converts the dimorphic SnSe2 to a fully hexagonal structure. To understand the mechanisms underlying the power factor improvement of Br-doped SnSe2, the electronic band parameters of Br-doped dimorphic and hexagonal SnSe2 should be evaluated separately. Using the single parabolic band model, we estimate the intrinsic mobility and effective mass of the Br-doped dimorphic and hexagonal SnSe2. While Br doping significantly improves the mobility of dimorphic SnSe2 (with the dominant hexagonal phase), it results in a combination of band convergence and band flattening in fully hexagonal SnSe2. Br-doped dimorphic SnSe2 is predicted to exhibit higher thermoelectric performance (zT ∼0.23 at 300 K) than Br-doped fully hexagonal SnSe2 (zT ∼0.19 at 300 K). Characterisation of the other, currently unidentified, structural phases of dimorphic SnSe2 will enable us to tailor the thermoelectric properties of Br-doped SnSe2.

Cold Sintering Mediated Engineering of Polycrystalline SnSe with High Thermoelectric Efficiency

Despite the attractive thermoelectric properties in single crystals, the fabrication of high-performance polycrystalline SnSe by a cost-effective strategy remains challenging. In this study, we prepare the undoped SnSe ceramic with remarkable thermoelectric efficiency by the combination of a cold sintering process (CSP) and thermal annealing. The high sintering pressure during CSP induces not only highly oriented grains but also a high concentration of lattice dislocations and stacking faults, which leads to large lattice strain that can shorten the phonon relaxation time. Meanwhile, the thermal annealing breaks the highly resistive SnOx layers at grain boundaries, which improves the electrical conductivity and power factor. In addition, the grain growth during annealing further turns the broken SnOx layers into nanoparticles, which further lowers the thermal conductivity by enhanced scattering. As a result, a peak ZT of 1.3 at 890 K and a high average ZT of 0.69 are achieved in the polycrystalline SnSe, suggesting great potential in mid-temperature power generation. This work may pave the way for the mass production of SnSe-based ceramics for thermoelectric devices.

Energy Interplay in Materials: Unlocking Next-Generation Synchronous Multisource Energy Conversion with Layered 2D Crystals

Layered 2D crystals have unique properties and rich chemical and electronic diversity, with over 6000 2D crystals known and, in principle, millions of different stacked hybrid 2D crystals accessible. This diversity provides unique combinations of properties that can profoundly affect the future of energy conversion and harvesting devices. Notably, this includes catalysts, photovoltaics, superconductors, solar-fuel generators, and piezoelectric devices that will receive broad commercial uptake in the near future. However, the unique properties of layered 2D crystals are not limited to individual applications and they can achieve exceptional performance in multiple energy conversion applications synchronously. This synchronous multisource energy conversion (SMEC) has yet to be fully realized but offers a real game-changer in how devices will be produced and utilized in the future. This perspective highlights the energy interplay in materials and its impact on energy conversion, how SMEC devices can be realized, particularly through layered 2D crystals, and provides a vision of the future of effective environmental energy harvesting devices with layered 2D crystals.

Highly oriented platinum/iridium thin films for high-temperature thermocouples with superior precision

The long-term precise high-temperature measurement of thin-film thermocouples (TFTCs) has attracted attention due to the capability of instantaneous temperature detection. However, related technologies have seen slow development, and there is no one standard TFTC yet. Here, we focus on a new strategy of reducing alloys for the easy preparation and performance enhancement of TFTCs via nanostructure and interface design. To this end, we fabricated a platinum/iridium (Pt/Ir) pure-element TFTC with a well matched interface and few defects, which demonstrated excellent long-term service stability over a high-temperature range. The corresponding polynomial fitting coefficients were ≥0.99999, indicating the accurate acquisition of temperature data. A reduced deviation (<0.21%) between three calibration cycles was obtained over a wide temperature range of 300 °C to 1000 °C, which is better than the maximum precision of a standard wire thermocouple. Superior properties are achieved because of the resulting fewer defects in the Pt and Ir thin films with highly preferential orientation along the (111) plane. The results indicate that our Pt/Ir TFTCs have significant potential for application in many domains such as thermal detection, microelectronics and aero-engines.

Defect governed zinc-rich columnar AZO thin film and contact interface for enhanced performance of thermocouples

The research on the stable thermoelectric properties and contact interface of high-precision thin-film thermocouples lags far behind the demand. In this study, a zinc-rich Al-doped ZnO (AZO) thin film was fabricated, in which the carriers were mainly donated by the Al dopant, and the oxygen defects migrated together, forming cage defects. Then, an indium tin oxide (ITO)/AZO thin-film thermocouple was prepared. It had a special temperature-dependent voltage curve due to the effects of cage defects on the thermoelectric properties of the AZO thin film and interfacial electron diffusion. When the zinc atoms in the cage defects were excited after annealing, a linear relationship between the temperature and voltage was obtained. The Seebeck coefficient of the thermocouple was constant at 168 μV K^-1 over the entire measured temperature range. In addition, the calculated error of the thermocouple was lower than 1% from 50 °C to 500 °C, showing good repeatability. These results showed that defect engineering could effectively be used to improve the temperature range stability of thermoelectric materials and optimize the precision of thin-film thermocouples.