RESUMEN
In this study, flexible thermoelectric coolers (FTECs) are used to develop an alternative personalized cooling technology to achieve a large temperature drop of 10 °C and cooling capacity of 256 W m-2 . Such an excellent cooling performance is attributed to the innovative design of the quadra-layered Ag2 Se/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate structure in FTECs and the induced air vortices by the vortex generator attached to the hot surface of the device. The applied pulse-width modulation technique guarantees human body comfort at inconsistent ambient temperature by modulating the duty ratio of the power source, which also saves 35% of the power consumption. As a result, the as-prepared FTECs only consume 68.5 W so as to maintain a comfortable skin temperature (32 ± 0.5 °C) when the ambient temperature is at 31 °C. This technology provides a reliable and adjustable solution for personalized cooling in environments where comfortable temperatures are exceeded.
RESUMEN
Owing to high intrinsic figure-of-merit implemented by multi-band valleytronics, GeTe-based thermoelectric materials are promising for medium-temperature applications. Transition metals are widely used as dopants for developing high-performance GeTe thermoelectric materials. Herein, relevant work is critically reviewed to establish a correlation among transition metal doping, electronic quality factor, and figure-of-merit of GeTe. From first-principle calculations, it is found that Ta, as an undiscovered dopant in GeTe, can effectively converge energy offset between light and heavy conduction band extrema to enhance effective mass at high temperature. Such manipulation is verified by the increased Seebeck coefficient of synthesized Ge1- x - y Tax Sby Te samples from 160 to 180 µV K-1 at 775 K upon doping Ta, then to 220 µV K-1 with further alloying Sb. Characterization using electron microscopy also reveals the unique herringbone structure associated with multi-scale lattice defects induced by Ta doping, which greatly hinder phonon propagation to decrease thermal conductivity. As a result, a figure-of-merit of ≈2.0 is attained in the Ge0.88 Ta0.02 Sb0.10 Te sample, reflecting a maximum heat-to-electricity efficiency up to 17.7% under a temperature gradient of 400 K. The rationalized beneficial effects stemming from Ta doping is an important observation that will stimulate new exploration toward high-performance GeTe-based thermoelectric materials.
RESUMEN
The coupling nature of thermoelectric properties determines that optimizing the Fermi level is the priority to achieve a net increase in thermoelectric performance. Conventionally, the carrier concentration is used as the reflection of the Fermi level in the band structure. However, carrier concentration strongly depends upon the material's effective mass, leading to that the optimal carrier concentration varies over a large scale for different materials. Herein, inspired by the big data survey, we develop a golden Seebeck coefficient range of 202-230 µV K-1 for thermoelectric semiconductors with lattice thermal conductivity of 0.4-1.5 W m-1 K-1. When the measured Seebeck coefficient reaches this range, the corresponding figure of merit is maximized. Using this approach, we exemplarily analyze the characteristics of n-type Pb1-xBixSe thermoelectric materials. With detailed electron microscopy and property characterizations, the high densities of dislocations and pores are found to be responsible for a low lattice thermal conductivity. Moreover, Bi substitution significantly tunes the Seebeck coefficient in a wide range. As a result, the Seebeck coefficient of â¼â¯-230 µV K-1 in Pb0.98Bi0.02Se is close to the golden range, leading to a figure of merit beyond 1.5. This finding provides an intuitive metric to determine the optimization extent of thermoelectric performance.