Thermoelectric Performance of 2D Tellurium with Accumulation Contacts

Abstract

Tellurium (Te) is an intrinsically p-type doped narrow bandgap semiconductor with excellent electrical conductivity and low thermal conductivity. Bulk trigonal Te has been theoretically predicted and experimentally demonstrated to be an outstanding thermoelectric material with high value of thermoelectric figure-of-merit ZT. In view of the recent progress in developing synthesis route of two-dimensional (2D) tellurium thin films as well as the growing trend of exploiting nanostructures as thermoelectric devices, here for the first time we report excellent thermoelectric performance of tellurium nanofilms, with room temperature power factor of 31.7 μW/cm•K 2 and ZT value of 0.63. To further enhance the efficiency of harvesting thermoelectric power in nanofilm devices, thermoelectrical current mapping was performed with a laser as a heating source, and we found high work function metals such as palladium can form rare accumulationtype metal-to-semiconductor contacts to 2D Te, which allows thermoelectrically generated carriers to be collected more efficiently. High-performance thermoelectric 2D Te devices have broad applications as energy harvesting devices or nanoscale Peltier coolers in microsystems.Thermoelectricity emerges as one of the most promising solutions to the energy crisis we are facing in 21 st century. It generates electricity by harvesting thermal energy from ambient or wasted heat, which is a sustainable and environmental-friendly route compared to consuming fossil fuels 1,2 . The efficiency of converting heat to electricity is evaluated by the key thermoelectrical figure of merit:= 2 , where is the Seebeck coefficient defined as = , and are electrical and thermal conductivity, V is the measured thermal voltage, and is the operating temperature. However the ZT value has not been significantly enhanced since 1960's 3 and so far the most state-of-the-art bulk materials can merely surpass 1 at room temperature 4,5 . This is because the parameters in defining ZT, Seebeck coefficient, electrical conductivity and thermal conductivity are usually correlated through the Wiedemann-Franz law 6-8 and by engineering one parameter, generally other parameters will compensate the change, which poses a dilemma for drastically improving ZT.For the past decades enormous efforts have been made to increase thermoelectric efficiency along two major pathways: either by developing new high-efficiency thermoelectric bulk materials, or by developing novel nano-structured thermoelectric materials 9 . From material perspective, the paradigm of an excellent thermoelectric material should be a heavily doped narrow-bandgap semiconductor with good conductivity meanwhile because of the existence of a finite bandgap, the separation of electrons and holes can avoid opposite contributions to the Seebeck coefficient.Also, heavy elements are preferred for thermoelectrical applications since they can enhance the ZT values by providing more effective phonon scattering centers and reducing the thermal conductivity 1,10 . Furthermore, vall...

High ZT 2D Thermoelectrics by Design: Strong Interlayer Vibration and Complete Band‐Extrema Alignment

“…However, because of the lower κ L, it shows better TE performance than KAgSe monolayer. The p‐type ZT at 700 K reaches an ultrahigh value of 2.08, which is significantly higher than those of recently reported promising nanoscale TE materials (0.025, 0.45, and 0.63 for SnSe nanosheets, single‐layer Bi 2 Se 3 , and Tellurium nanofilms) [ 36,37,39 ] and Ag‐based bulk TE materials (0.7, 0.85, and 0.9 for CsAg 5 Te 3 , Ag 8 SnSe 6 , and AgBi 3 S 5 , respectively) [ 40–44 ] (Figure 5g). More importantly, such a high ZT, only realized in bulk SnSe (2.6 ± 0.3) [ 45 ] and microscale Ge‐alloyed SnSe (≈2.1), [ 46 ] will be of important practical significance for nanoscale TE applications.…”

Two-Dimensional Tellurium: Progress, Challenges, and Prospects

“…In general, two solutions have been proposed to improve thermoelectric generation efficiency: striving to develop high-efficiency thermoelectric bulk materials or low-dimension thermoelectric materials. As previously mentioned, a large body of theoretical and experimental investigations has proved that 2D Te possesses extraordinary thermoelectric properties, even among the other 2D materials [185,[201][202][203][204][205]. Thus, 2D…”

In-plane anisotropic electronics based on low-symmetry 2D materials: progress and prospects

“…Tellurene, therefore, is expected to rival black phosphorus in many applications. 15,60,[69][70][71][72][73][74]…”

“…[1][2][3][4][5][6] Even though graphene has extremely large mobility and outstanding electron-transport properties, the absence of a band gap restricts its applications in (opto) electronic devices. Beyond graphene, 2D layered materials have become more and more popular among researchers due to their unique structural, 7,8 mechanical, 9 electrical, 10,11 thermoelectric, [12][13][14][15] optical, [16][17][18][19][20][21][22] catalytic, 23,24 and sensing properties,. [25][26][27][28][29][30] Transition metal dichalcogenides (TMDCs) with tunable band gap fully exert the advantages in low-cost, exible, and highperformance logic and optoelectronic devices, such as eldeffect transistors (FETs), photodetectors, photonic devices and solar cells.…”