The best thermoelectric.

Abstract

What electronic structure provides the largest figure of merit for thermoelectric materials? To answer that question, we write the electrical conductivity, thermopower, and thermal conductivity as integrals of a single function, the transport distribution. Then we derive the mathematical function for the transport distribution, which gives the largest figure of merit. A delta-shaped transport distribution is found to maximize the thermoelectric properties. This result indicates that a narrow distribution of the energy of the electrons participating in the transport process is needed for maximum thermoelectric efficiency. Some possible realizations of this idea are discussed.Thermoelectric materials can be used to make refrigerators or power generators (1, 2). These solid state devices have no moving parts and are extremely reliable. Their efficiency is low, so they are used in products where reliability is more important than efficiency. Thermoelectric refrigerators are used to spot cool electronic components such as infrared sensors or computer chips. Power generators are used in space stations and satellites.There has been much effort to find the best thermoelectric materials (1-3). There has also been numerous discussion of the physical limits-i.e., what are the best possible thermoelectrics allowed by nature (4)? Here we provide a new and simple estimate of the maximum efficiency of thermoelectric materials. The efficiency of thermoelectric energy converters depends on the transport coefficients of the constituent materials through the figure of merit (1): a-S2where a-is the electrical conductivity and S is the Seebeck coefficient. The quantity in the denominator is the thermal conductivity; it is given by the sum of contributions from the electronic carriers Ke and the lattice KI. The efficiency is increased by making ZT as large as possible, where T is the mean operating temperature of the device. At room temperature, the best thermoelectric material now known is Bi2Te3, which has ZT 1 (1, 2). With this value, the coefficient of performance of thermoelectric coolers is about one-third the value for conventional compressor systems. At room temperature, with the current design, thermoelectric refrigerators will be competitive with conventional compressor systems if a material is found with ZT 4. However, any small increment in this value (ZT 2 1) will result in many new applications for these devices. This technology is environmentally cleaner and more reliable than traditional compressor systems. Therefore, it is worth exploring the possibility of increasing ZT to find a material with ZT >

Promising thermoelectric properties of phosphorenes

“…Thermoelectric efficiency sufficient for technological applications might be only possible at high temperatures for black-P. On the other hand, our ballistic quantum transport investigation conspicuously indicates the much better thermoelectric performance of blue-P. We attribute the rather higher maximum ZT values of blue-P to its high power factor resulting from the large slope in the transmission function around band edges, in agreement with the Mahan−Sofo criteria [54]. Table 1.…”

Thermoelectric properties of a weakly coupled quantum dot: enhanced thermoelectric efficiency

“…We note that the position of the two strong maxima are in agreement with the predicted maximization of S 2 GT and ZT in materials with delta-like density of states [12]. Moreover, according to Eq.…”

“…Moreover, according to Eq. (13), the absolute magnitude of S that corresponds to the optimization of S 2 GT is 2.4k B /e = 207 µV/K which is in absolute agreement with the value predicted in [12]. At this point we should remark that Eq.…”

“…Mahan and Sofo [12] predicted a maximization of the thermoelectric efficiency in materials with a delta-like density of states. This suggests that quantum dots and molecular junctions are promising candidates for good thermoelectric materials.…”

One-Dimensional Quantum Confinement Effect Modulated Thermoelectric Properties in InAs Nanowires

“…Originally, it was believed that the thermoelectric power factor is always maximized when the Fermi level is placed right at the position of singular DOS and smaller number of subbands is preferred. 10,11 Our experiment indicates that the general idea of utilizing singular DOS to modulate the power factor in nanomaterials is effective. However, several important questions remain to be understood further such as where the optimal Fermi energy lies and if the system has to be in the single subband regime.…”