Non-conventional charge transport in organic semiconductors: magnetoresistance and thermoelectricity

Fenwick, Oliver; Orgiu, Emanuele

doi:10.1039/c6me00079g

Cited by 3 publications

(5 citation statements)

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“…Since the response of OMAR devices to a magnetic field originates from hyperfine field ( B hf )-induced spin-selective routes through a spin-mixing effect, the magnetic sensitivity should be directly related to the shape of the magnetoresistance (MR) curves. The OMAR ratio has been defined as , where R (0) is the resistance at magnetic field B = 0 . MR curves of organic OMAR devices should fit well with either a Lorentz function for saturated line shape (where B 0 is the half-width at half-maximum) or with a non-Lorentz empirical law without clear saturation (where B 1 is the half-width at quarter-maximum) .…”

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confidence: 99%

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Organic Single-Crystal Spintronics: Magnetoresistance Devices with High Magnetic-Field Sensitivity

Ding

Tian

et al. 2019

ACS Nano

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Organic spintronics is a new emerging field that deals with the spin-related phenomena of organic materials under the influence of a magnetic field. However, there remain some challenges in organic spintronics including (i) low conductivity and massive disorders of organic thin films blocking the way to controllable spin transport, (ii) relatively low magnetic-field sensitivity of organic magnetoresistance (OMAR) devices with tangled working mechanisms and short of methods for sensitivity improvement. Here, we report the realization of OMAR devices based on organic single crystals. The lesser amount of impurities and defects in crystals guarantees a reduction in spin and charge scatterings, so that the OMAR devices exhibit both a small Lorentz function fitting parameter B 0 of 2.3 mT and a non-Lorentz function fitting parameter B 1 of 0.86 mT in the strictly limited bipolaron model. Moreover, we demonstrate the effect of aggregation and intrinsic trap states, pointing out a way for the improvement of the sensitivity.

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confidence: 99%

“…, where R(0) is the resistance at magnetic field B = 0. 16 MR curves of organic OMAR devices should fit well with either a Lorentz function…”

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confidence: 99%

Organic Single-Crystal Spintronics: Magnetoresistance Devices with High Magnetic-Field Sensitivity

Ding

Tian

et al. 2019

ACS Nano

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“…Electrostatic modeling of the interface energetics suggests that bipolarons are generally expected to be significant (i.e., >1% of the polaron concentration) for energetically broad interface DOS distributions at contacts in the Fermi level pinning regime. In this context, bipolarons may also be significant at other interfaces that sustain high charge density in a broadened interfacial DOS, such as the channel of organic thin film transistors 19 , 33 , which might be exploited to create devices with new magnetic functionality.…”

Section: Discussionmentioning

confidence: 99%

Large bipolaron density at organic semiconductor/electrode interfaces

et al. 2017

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Bipolaron states, in which two electrons or two holes occupy a single molecule or conjugated polymer segment, are typically considered to be negligible in organic semiconductor devices due to Coulomb repulsion between the two charges. Here we use charge modulation spectroscopy to reveal a bipolaron sheet density >1010 cm−2 at the interface between an indium tin oxide anode and the common small molecule organic semiconductor N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine. We find that the magnetocurrent response of hole-only devices correlates closely with changes in the bipolaron concentration, supporting the bipolaron model of unipolar organic magnetoresistance and suggesting that it may be more of an interface than a bulk phenomenon. These results are understood on the basis of a quantitative interface energy level alignment model, which indicates that bipolarons are generally expected to be significant near contacts in the Fermi level pinning regime and thus may be more prevalent in organic electronic devices than previously thought.

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“…[ 52–56 ] Over the past years, scientists have managed to increase the ZT values of organic thermoelectric materials via molecular design, phonon, and electron transport decoupling, and production of hybrid composites incorporating high thermoelectric particles. [ 57–69 ]…”

Section: Introductionmentioning

confidence: 99%

“…[52][53][54][55][56] Over the past years, scientists have managed to increase the ZT values of organic thermoelectric materials via molecular design, phonon, and electron transport decoupling, and production of hybrid composites incorporating high thermoelectric particles. [57][58][59][60][61][62][63][64][65][66][67][68][69] In this review, the thermoelectric performances of the organic single-component materials, hybrid composites, and novel ionogels developed over the last several years are discussed separately in terms of the respective parameter tuning and pathway optimization. The current state of the art of organic thermoelectric materials is primarily highlighted based on their structure-property relationship.…”

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confidence: 99%

Soft Organic Thermoelectric Materials: Principles, Current State of the Art and Applications

Zhang

Wang

Zhang

et al. 2021

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heat engines and transforming the asgenerated mechanical energy into electricity. [2][3][4][5] Compared with traditional unsustainable method, thermoelectric materials, which can transform the temperature gradient from waste heat or solar thermal energy into electricity through the Seebeck effect, have triggered great interest in the development of wearable cooling/heating devices and low-temperature energy generators. [6][7][8][9][10][11][12][13][14][15][16][17] Inorganic thermoelectric materials exhibit superior thermoelectric figure of merit than the organic ones, but their low abundance, high-cost, heaviness, and brittleness usually prevents their applications for flexible and/or nontoxic devices. [18][19][20][21][22][23][24] In contrast, organic thermoelectric materials present intrinsically low thermal conductivity and high mechanical flexibility, making them versatile in green energy harvesting and thermoelectric refrigeration (Figure 1). [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] The energy conversion efficiency of the thermoelectric materials can be estimated by the dimensionless figure of merit ZT = S 2 σT/κ, where S is the thermopower or Seebeck coefficient, σ is electrical conductivity of materials, T is the absolute temperature, and κ represents the thermal conductivity. [43][44][45][46][47][48][49][50][51] Superficially, increasing S and σ, and decreasing κ can infinitely raise the value of ZT. However, the strong interdependence among these three parameters is extremely challenging. [52][53][54][55][56] Over the past years, scientists have managed to increase the ZT values of organic thermoelectric materials via molecular design, phonon, and electron transport decoupling, and production of hybrid composites incorporating high thermoelectric particles. [57][58][59][60][61][62][63][64][65][66][67][68][69] In this review, the thermoelectric performances of the organic single-component materials, hybrid composites, and novel ionogels developed over the last several years are discussed separately in terms of the respective parameter tuning and pathway optimization. The current state of the art of organic thermoelectric materials is primarily highlighted based on their structure-property relationship. In particular, the marvelous progress that has allowed organic thermoelectric materials to compete with traditional inorganic compounds is described. Finally, organic thermoelectric generators containing different legs with variousoutput powers and their multiple applications are briefly summarized.The enormous demand for waste heat utilization and burgeoning ecofriendly wearable materials has triggered huge interest in the development of thermoelectric materials that can harvest low-cost energy resources by converting waste heat to electricity efficiently. In particular, due to their high flexibility, nontoxicity, cost-effectivity, and promising applicability in various fields, organic thermoelectric materials are drawing more attention compared with their toxic, expensive, he...

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Non-conventional charge transport in organic semiconductors: magnetoresistance and thermoelectricity

Abstract: Magnetoresistance and thermoelectricity require additional properties of materials beyond their ability to transport charge, namely a large resistive response to a magnetic field, or in the case of thermoelectrics a large Seebeck coefficient combined with low thermal conductivity.

Cited by 3 publications

References 133 publications

Organic Single-Crystal Spintronics: Magnetoresistance Devices with High Magnetic-Field Sensitivity

Organic Single-Crystal Spintronics: Magnetoresistance Devices with High Magnetic-Field Sensitivity

Large bipolaron density at organic semiconductor/electrode interfaces

Soft Organic Thermoelectric Materials: Principles, Current State of the Art and Applications

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