Search

Toward high-performance thermoelectric energy conversion, the electrons and holes must work jointly like two wheels of a cart: if not longitudinally, then transversely. The bipolar effect — the main performance restriction in the traditional longitudinal thermoelectricity, can be manipulated to be a performance enhancer in the transverse thermoelectricity. Here, we demonstrate this idea in semimetal Mg2Pb. At 30 K, a giant transverse thermoelectric power factor as high as 400 μWcm−1K−2 is achieved, a 3 orders-of-magnitude enhancement than the longitudinal configuration. The resultant specific heat pumping power is ~ 1 Wg−1, higher than those of existing techniques at 10~100 K. A large number of semimetals and narrow-gap semiconductors making poor longitudinal thermoelectrics due to severe bipolar effect are thus revived to fill the conspicuous gap of thermoelectric materials for solid-state applications. Heat pumping is in high demand at cryogenic temperature, but whether thermoelectricity can take on cryogenic heat pumping is an open question. Here, the authors answer this question by leveraging bipolar effect to enhance transverse thermoelectricity in semimetal Mg2Pb for cryogenic heat pumping. [ABSTRACT FROM AUTHOR]

Poly(3-hexylthiophene) (P3HT) films were prepared by using raw P3HT powders with different molecular configurations through solution processing and doped with ferric salt of triflimide anions [Fe(TFSI)], and their thermoelectric (TE) properties were studied. It was found that P3HT with highly regular molecular configuration formed highly ordered chain arrangements in P3HT film (denoted rr-P3HT film), while P3HT with irregular molecular configuration formed random chain arrangements in P3HT film (denoted ra-P3HT film). The ordered chain arrangement in rr-P3HT not only improved the charge carrier mobility but also contributed to produce more carriers, thereby remarkably improving the electrical conductivity. The electrical conductivity of rr-P3HT film was up to 96.1 S/cm, more than two orders of magnitude higher than that of ra-P3HT film. Consequently, the power factor of rr-P3HT film reached 17.10 μW/(m K), about one order of magnitude higher than that of ra-P3HT film and among the best values for pure P3HT TE materials. This study suggests that P3HT with highly regular configuration contributes to form highly ordered molecular chain arrangements, resulting in improved TE properties. [ABSTRACT FROM AUTHOR]

International transport property-measurement round-robins have been conducted by the thermoelectric annex under the International Energy Agency (IEA) Implementing Agreement on Advanced Materials for Transportation (AMT). Two previous round-robins used commercially available bismuth telluride as the test material, with the objectives of understanding measurement issues and developing standard testing procedures. This round-robin extended the measurement temperature range to 773 K. It was designed to meet the increasing demands for reliable transport data for thermoelectric materials used for power-generation applications. Eleven laboratories from six IEA-AMT member countries participated in the study. A half-Heusler ( n-type) material prepared by GMZ Energy was selected for the round-robin. The measured transport properties had a narrower distribution of uncertainty than previous round-robin results. The study intentionally included multiple testing methods and instrument types. Over the full temperature range, the measurement discrepancies for the figure of merit, ZT, in this round-robin were ±11.5 to ±16.4% from the averages. [ABSTRACT FROM AUTHOR]

The fundamental understanding of the influence of molecular structure on the carrier transport properties in the field of organic thermoelectrics (OTEs) is a big challenge since the carrier transport behavior in conducting polymers reveals average properties contributed from all carrier transport channels, including those through intra-chain, inter-chain, inter-grain, and hopping between disordered localized sites. Here, combining molecular dynamics simulations and experiments, we investigated the carrier transport properties of doped highly oriented poly(3-hexylthiophene) (P3HT) films with different side-chain regioregularity. It is demonstrated that the substitution of side chains can not only take effect on the carrier transport edge, but also on the dimensionality of the transport paths and as a result, on the carrier mobility. Conductive atomic force microscopy (C-AFM) study as well as temperature-dependent measurements of the electrical conductivity clearly showed ordered local current paths in the regular side chain P3HT films, while random paths prevailed in the irregular sample. Regular side chain substitution can be activated more easily and favors one-dimensional transport along the backbone chain direction, while the irregular sample presents the three-dimensional electron hopping behavior. As a consequence, the regular side chain P3HT samples demonstrated high carrier mobility of 2.9 ± 0.3 cm2/V·s, which is more than one order of magnitude higher than that in irregular side chain P3HT films, resulting in a maximum thermoelectric (TE) power factor of 39.1 ± 2.5 μW/mK2 at room temperature. These findings would formulate design rules for organic semiconductors based on these complex systems, and especially assist in the design of high performance OTE polymers. [ABSTRACT FROM AUTHOR]

The low weighted carrier mobility has long been considered to be the key challenge for improvement of thermoelectric (TE) performance in BiTeI. The Rashba-effect-induced two-dimensional density of states in this bulk semiconductor is beneficial for thermopower enhancement, which makes it a prospective compound for TE applications. In this report, we show that intercalation of minor Cu-dopants can substantially alter the equilibria of defect reactions, selectively mediate the donor-acceptor compensation, and tune the defect concentration in the carrier conductive network. Consequently, the potential fluctuations responsible for electron scattering are reduced and the carrier mobility in BiTeI can be enhanced by a factor of two to three between 10 K and 300 K. The carrier concentration can also be optimized by tuning the Te/I composition ratio, leading to higher thermopower in this Rashba system. Cu-intercalation in BiTeI gives rise to higher power factor, slightly lower lattice thermal conductivity, and consequently improved figure of merit. Compared with pristine BiTe0.98I1.02, the TE performance in Cu0.05BiTeI reveals a 150% and 20% enhancement at 300 and 520 K, respectively. These results demonstrate that defect equilibria mediated by selective doping in complex TE and energy materials could be an effective approach to carrier mobility and performance optimization. [ABSTRACT FROM AUTHOR]

The intrinsic ultra-low lattice thermal conductivity ( κ L ) of high performance thermoelectric Cu 2 S may arise from its multiform complex crystal structures while the further sharp drop of κ L observed at elevating temperatures close to the phase transition to hexagonal high-chalcocite is of considerable interest. In this work, in-depth in-situ transmission electron microscopy investigations have been performed by either heating or electron irradiation to analyze the structural evolution of Cu 2 S. Multiple including new phase structures have been observed in Cu 2 S. Upon increasing the temperature, drastic structural changes took place including phase transition among different phases, formation of an intermediate phase, switching of crystal orientation and inverse phase transitions, which indicate multiple forms of Cu ordering with high temperature-sensitivity. Such tremendous structural evolution along with formation and movement of phase boundaries are believed to strongly scatter the phonons. [ABSTRACT FROM AUTHOR]

The interfacial stability of thermoelectric (TE) joints is among the key issues determining the durability of thermoelectric generators (TEGs) in practical operation. For skutterudite (SKD) based TEGs, the inter-diffusion between the metal electrode and the SKD material at high temperature plays a vital role on the interfacial stability of the joints. In this work, we report the evolution of the interfacial microstructure and the interfacial contact resistivity for a series of p-type SKD TE joints (Ti/Ce y Fe x Co 4 -x Sb 12 , x = 1.5–4, y = 0.35–1) at high temperature. The growth of the intermetallic compound (IMC) layers at the interface of all the joints was found to be controlled by the diffusion process. In contrast to the binary Ti/CoSb 3 joints, the growth of the interfacial IMC layers in the p-type Ti/Ce y Fe x Co 4 -x Sb 12 joints was considerably depressed. Moreover, no brittle TiCoSb phase was formed at the interface of the p-type joints, which resulted in good stability of the interfacial contact resistivity at high temperature. Related mechanisms were discussed. [ABSTRACT FROM AUTHOR]

Highly (001)-oriented Cu 2- y Se thin films with tunable thermoelectric performances have been grown by pulsed laser deposition. By using targets with different Cu/Se ratios that further determines the copper deficiency of as-grown films, the carrier concentrations of as-grown films are tuned within a broad range from 10 18 to 10 21 cm −3 . The optimum performance is observed at carrier concentration ~1.58×10 20 cm −3 . The distinct properties of Cu 2- y Se thin films with nearly ideal chemical stoichiometric ratio are observed. In addition, a weak change in the electrical transport during the second-order phase transition was observed in the thin films due to the anisotropic structure of the Cu 2- y Se. [ABSTRACT FROM AUTHOR]