Activated hopping transport in anisotropic systems at low temperatures

Ihnatsenka, S.

doi:10.1103/physrevb.94.195202

Cited by 8 publications

(13 citation statements)

References 32 publications

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“…Due to the lamellar nature of typical PEDOT:PSS morphologies, conductivities tend to be highly anisotropic, which can also be understood in a VRH framework. [103][104][105] As no reliable data are available regarding anisotropy in thermopower, this topic will not be discussed and we will focus on in-plane geometries. It should, moreover, be kept in mind that there exist large differences in formulations and associated morphologies of PEDOT:PSS and one can therefore not automatically generalize individual results to the whole material system.…”

Section: Pedot:pssmentioning

confidence: 99%

Conjugated Polymer Blends for Organic Thermoelectrics

Zuo

Abdalla

Kemerink

2019

Adv Elect Materials

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A major attraction of organic conjugated semiconductors is that materials with new, emergent functionality can be designed and made by simple blending, as is extensively used in e.g. bulk heterojunction organic solar cells. Here, we critically review doped blends based on organic semiconductors (OSC) for thermoelectric applications. Several experimental strategies to improve thermoelectric performance, measured in terms of power factor (PF) or figure-ofmerit ZT, have been demonstrated in recent literature. Specifically, density-of-states design in blends of 2 OSCs can be used to obtain electronic Seebeck coefficients up to ∼2000 µV/K. Alternatively, blending with (high-dielectric constant) insulating polymers can improve doping efficiency and thereby conductivity, as well as induce more favorable morphologies that improve conductivity while hardly affecting thermopower. In the PEDOT:PSS blend system, processing schemes to either improve conductivity via morphology or via (partial) removal of the electronically isolating PSS, or both, have been demonstrated. Although a range of experiments have at least quasi-quantitatively been explained by analytical or numerical models, a comprehensive model for organic thermoelectrics is lacking so far.Strategies to increase thermoelectric performance of doped organic semiconductors by blending are reviewed. Experimental results are, where possible, compared to analytical and numerical models. Several promising strategies to increase conductivity and/or thermopower are experimentally identified in recent literature. In contrast, formal understanding, especially of the role of morphology, is somewhat lagging behind.

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Section: Pedot:pssmentioning

confidence: 99%

Conjugated Polymer Blends for Organic Thermoelectrics

Zuo

Abdalla

Kemerink

2019

Adv Elect Materials

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“…3(c), then the electrons adjust their path further in the perpendicular direction to find a site to hop in that is closer in energy. 15 The average hopping length might be estimated from the length of individual current segments, which is 2.12l and 2.07l in Figs. 3(b) and (c), respectively.…”

Section: Resultsmentioning

confidence: 99%

“…10 The method to find conductivity σ and current densities I is described in Ref. 15. The system is assumed to be in a linear Ohmic regime.…”

Section: Modelmentioning

confidence: 99%

“…Furthermore, the density of states (DOS) was taken exponential, 5,6 which contradicts an overwhelming number of studies, which have pointed out that Gaussian DOS is more accurate for disordered organic semiconductors, [11][12][13][14] including P3TH. 13 For anisotropic organic semiconductors, the charge hoping theory has been previously applied to study Mott's exponents, 15,16 hopping length 17 and polaron effects on mobility. 18 A typical organic semiconductor contains a blend of conducting polymer molecules, dopants and insulating host molecules.…”

Section: Introductionmentioning

confidence: 99%

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Model of the thermoelectric properties of anisotropic organic semiconductors

Ihnatsenka

2021

Preprint

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A model of hopping charge transport that accounts for anisotropy of localized states is proposed. For the localized states that are highly anisotropic in space, the degree of orientation relates exponentially to the ratio of conductivities in parallel and perpendicular directions, while the ratio of Seebeck coefficients stays nearly unaffected. Coulomb interaction preserves these dependencies. However, the ratio of Seebeck coefficients can increase if Coulomb interaction is screened more strongly in a direction parallel to the predominant orientation of the localized states. The relationship to experimental data on tensile drawn and ribbed polymer films is also discussed.

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“…In addition to the largely studied black phosphorus [6], a vast number of anisotropic 2D materials have been explored recently, including for instance group-IV monochalcogenide (e.g., GeS [7]), low-symmetry transition-metal dichalcogenides (e.g., ReS 2 [8]), low-symmetry metal chalcogenide(s) (e.g., GaTe [9]), and the most recently discovered group-IV−V compounds (e.g., GeAs [10,11], GeP [12]). Due to their ultrathin nature, the physical properties of anisotropic 2D materials are expected to be highly sensitive to inevitable structural defects and extrinsic charged impurities [13] as well as to many other factors, e.g., substrates, environment, and surface roughness [14]. In particular, it is reasonable to believe that these extrinsic elements will significantly alter the intrinsic electrical anisotropic conduction in these materials.…”

Section: Introductionmentioning

confidence: 99%

Impact of Impurities on the Electrical Conduction of Anisotropic Two-Dimensional Materials

et al. 2020

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Anisotropic two-dimensional materials possess intrinsic angle-dependent physical properties that originate from their low crystal symmetry. Yet, how these properties are affected by external impurities or structural defects in the material is still wholly unclear. Here, we address this question by investigating the electrical transport in the anisotropic layered model system germanium arsenide. First, we show that the ratio of conductivities along the armchair and zigzag crystallographic directions exhibits an intriguing dependence with respect to both temperature and carrier density. Then, by using a conceptually simple model, we demonstrate that this unexpected behavior is directly related to the presence of impurityinduced localized states in the band gap that introduce isotropic hopping conduction. The presence of this conduction mechanism in addition to the intrinsic band conduction significantly influences the anisotropic electrical properties of the material, especially at room temperature, i.e., at application-relevant conditions.

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Activated hopping transport in anisotropic systems at low temperatures

Cited by 8 publications

References 32 publications

Conjugated Polymer Blends for Organic Thermoelectrics

Conjugated Polymer Blends for Organic Thermoelectrics

Model of the thermoelectric properties of anisotropic organic semiconductors

Impact of Impurities on the Electrical Conduction of Anisotropic Two-Dimensional Materials

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