Violation of the Wiedemann-Franz law in quasi-one-dimensional organic crystals

Casian, A.

doi:10.1103/physrevb.81.155415

Cited by 43 publications

(24 citation statements)

References 20 publications

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“…Zintl compounds [13] and skutterudites [14] , have been evaluated as good thermoelectric 3 candidates due to reduced lattice thermal conductivity and electronic band structure tunability. These optimization strategies, together with the ability for low-cost production and low-temperature processibility, have recently raised interest in organic polymers [15] , such as PEDOT:Tos, reaching = 0.25 at room temperature (RT) [4] and thus advancing the value of = 1.2 obtained for Bi2Te3 (the best RT thermoelectric material to date [7] ). Herein, quasi-1D organic conductors based on small molecules constitute a new, sustainable approach towards organic thermoelectrics that provide many of the desired electrical and thermal properties described above.…”

Section: Low-cost and Sustainable Organic Thermoelectrics Based On Lomentioning

confidence: 99%

Low‐Cost and Sustainable Organic Thermoelectrics Based on Low‐Dimensional Molecular Metals

et al. 2017

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A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription.For more information, please contact eprints@nottingham.ac.uk 1 DOI: 10.1002/((please add manuscript number)) Article type: Communication Low-Cost and Sustainable Organic Thermoelectrics Based on LowDimensional Molecular MetalsBy Florian Huewe*, Alexander Steeger*, Kalina Kostova, Laurence Burroughs, Irene Bauer, Peter Strohriegl, Vladimir Dimitrov, Simon Woodward and Jens Pflaum* F. Huewe [ †] , A. Steeger [ †] The dimensionless figure of merit measures a material's thermoelectric performancewhere electrical conductivity (resistivity ), Seebeck coefficient/thermopower , and thermal conductivity provide the power factor = 2 . Materials with high electrical conductivity and thermopower but low thermal conductivity are desirable to maximize and hence, the thermoelectric conversion efficiency. Approximately, is inversely proportional to which in turn is related to the electronic thermal conductivity el = via the Wiedemann-Franz (WF) law.Advances in have been achieved by tuning the doping of semiconductors to maximize the [6] together with reducing the phononic contribution to thermal conduction by means of nanostructured superlattice architectures [7,8] . To overcome the inherent limitations of ordinary materials, a dimensionality reduction of the electronic system has been proposed [9] . This can lead to a violation of the WF law [10,11] and to phonon drag contributions to the thermopower [12] . Complex crystal structures, e.g. Zintl compounds [13] and skutterudites [14] , have been evaluated as good thermoelectric 3 candidates due to reduced lattice thermal conductivity and electronic band structure tunability. These optimization strategies, together with the ability for low-cost production and low-temperature processibility, have recently raised interest in organic polymers [15] , such as PEDOT:Tos, reaching = 0.25 at room temperature (RT) [4] and thus advancing the value of = 1.2 obtained for Bi2Te3 (the best RT thermoelectric material to date [7] ). Herein, quasi-1D organic conductors based on small molecules constitute a new, sustainable approach towards organic thermoelectrics that provide many of the desired electrical and thermal properties described above. Additionally, they are lightweight and thermodynamically stable allowing for portable device manufacturing and long-term usage. In comparison to organic polymers the availability of electrically high-performing p-and ntype organic conductors facilitates the construction of all-organic thermoelectric devices.As a starting point we chose two of the best p-and n-type conducting radical ion salts, TTT2I3 (TTT = Tetrathiotetracene) and (DMe-DCNQI)2Cu (DMe-DCNQI = Dimethyl-Dicyanoquinonediimine).They form macroscopic needle-like sin...

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Section: Low-cost and Sustainable Organic Thermoelectrics Based On Lomentioning

confidence: 99%

Low‐Cost and Sustainable Organic Thermoelectrics Based on Low‐Dimensional Molecular Metals

et al. 2017

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“…confined dimensions 12,13 such as nano-wires, [14][15][16] quasi-1D systems, [17][18][19] and effective 0-D systems such as quantum dots, [20][21][22] , single molecule [23][24][25] and single atom 26 systems; under conditions of quantum criticality; [27][28][29][30][31] in superconductors; 16,[32][33][34][35][36][37][38] in superlattices and granular metals; [39][40][41][42][43] and in the presence of disorder.…”

mentioning

confidence: 99%

On the Lorenz number of multiband materials

2017

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There are many exotic scenarios where the Lorenz number of the Wiedemann-Franz law is known to deviate from expected values. However, in conventional semiconductor systems, it is assumed to vary between the values of ∼1.49 × 10 −8 W Ω K −2 for non-degenerate semiconductors and ∼2.45 × 10 −8 W Ω K −2 for degenerate semiconductors or metals. Knowledge of the Lorenz number is important in many situations, such as in the design of thermoelectric materials and in the experimental determination of the lattice thermal conductivity. Here we show that, even in the simple case of two and three band semiconductors, it is possible to obtain substantial deviations of a factor of two (or in the case of a bipolar system with a Fermi level near the midgap, even orders of magnitude) from expectation. In addition to identifying the sources of deviation in unipolar and bipolar two-band systems, a number of analytical expressions useful for quantifying the size of the effect are derived. As representative case-studies, a three-band model of the materials of lead telluride (PbTe) and tin sellenide (SnSe), which are important thermoelectric materials, is also developed and the size of possible Lorenz number variations in these materials explored. Thus, the consequence of multi-band effects on the Lorenz number of real systems is demonstrated.

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“…The TTT crystal spacing was so large ( Figure 3) that attempted deposition of the top (Al) electrode lead only to short circuiting through penetration to the basal electrode. In the case of needle-shaped organic crystals electrical conductivity measured longitudinally can be several orders of magnitude higher than transversal conductivity [9]. Hilti et al reported the anisotropy of conductivity in (TTT) 2 I 3 crystals is between 100 and 1000 [21].…”

Section: Resultsmentioning

confidence: 99%

“…One class of candidates for TE devices are radical cation salts attained by oxidation of tetrathiotetracene (TTT, Figure 1) [6][7][8], such as ditetrathiotetracene triiodide [9]. The TE performance of these salts is often compromised if non pristine TTT starting material is used and (low) electrical conductivity of the initial TTT is frequently the best indicator of its purity [9]. Large, good quality organic crystals with low impurity/defect concentrations often have higher electrical conductivity than polycrystalline films, but are challenging to grow.…”

Section: Introductionmentioning

confidence: 99%