High Seebeck Coefficient in Mixtures of Conjugated Polymers

Zuo, Guangzheng; Liu, Xianjie; Fahlman, Mats; Kemerink, Martijn

doi:10.1002/adfm.201703280

Cited by 91 publications

(107 citation statements)

References 23 publications

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“…On the other hand, S is known to be proportional to the energy difference between the Fermi level ( E F ) and the transport level ( E t ) in the case of a hopping transport‐dominant system . Therefore, S of conjugated polymers generally shows a decreasing trend with doping since E F approaches E t because of increased carrier densities . It seems that in our system, doping saturation occurred at ϕ BCF of ≈40.5 mol%.…”

Section: Resultsmentioning

confidence: 76%

“…[42][43][44] Therefore, S of conjugated polymers generally shows a decreasing trend with doping since E F approaches E t because of increased carrier densities. [43][44][45][46] It seems that in our system, doping saturation occurred at φ BCF of ≈40.5 mol%. A further increase in φ BCF beyond 40.5 mol% led to the growth of BCF crystals in the composite films (see the optical Adv.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Self‐Healable and Stretchable Organic Thermoelectric Materials: Electrically Percolated Polymer Nanowires Embedded in Thermoplastic Elastomer Matrix

Jeong

Jung

Suh

et al. 2019

Adv Funct Materials

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Self‐healable and stretchable energy‐harvesting materials can provide a new avenue for the realization of self‐powered wearable electronics, including electronic skins, whose main materials are required to be robust to and stable under external damage and severe mechanical stresses. However, thermoelectric (TE) materials showing both self‐healing properties and stretchability have not yet been demonstrated despite their great potential to harvest thermal energy in the human body. As most existing TE materials are either mechanically brittle or unrecoverable after being subjected to damage, a novel approach is necessary for designing such materials. Herein, self‐healable and stretchable TE materials based on all‐organic composite system wherein polymer semiconductor nanowires are p‐doped with a molecular dopant and embedded in a thermoplastic elastomer matrix are reported. The polymer nanowires are electrically percolated in the matrix, and the resulting composite materials exhibit good TE performance. The composites also exhibit both excellent self‐healing properties under mild heat and pressure conditions and good stretchability. It is believed that this work can be a cornerstone for the design of self‐healable and stretchable energy‐harvesting materials as it provides useful guidelines for imparting electrical conductivity to insulating thermoplastic elastomers, which typically possess versatile and useful mechanical properties.

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Section: Resultsmentioning

confidence: 76%

Section: Resultsmentioning

confidence: 99%

Self‐Healable and Stretchable Organic Thermoelectric Materials: Electrically Percolated Polymer Nanowires Embedded in Thermoplastic Elastomer Matrix

Jeong

Jung

Suh

et al. 2019

Adv Funct Materials

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“…This leads to a strong increase in S, albeit at the cost of a lower conductivity. [18] Indeed, we observe an overall decrease in conductivity with increasing NDI-CN fraction in Figure 2a,b that is accompanied by an obvious peak in S for inverse-sequential doping at 1 wt% NDI-CN. Surprisingly, a negligible increase in S occurs at the same concentrations for bulk doping.…”

Section: High Seebeck Coefficient and Power Factor In N-type Organic mentioning

confidence: 95%

“…[18] This is relevant to low-power, low-cost systems, where voltage and price are more important than power, for example, in thermometry or to supply an autonomous sensor or a reflective LCD display with electricity. [18][19][20] Specifically, we add lower-LUMO material, NDI-CN, [21] into the PCBM solution, causing the formation of a second "trap" maximum in the electron density of states, cf. Figure 1.…”

Section: High Seebeck Coefficient and Power Factor In N-type Organic mentioning

confidence: 99%

High Seebeck Coefficient and Power Factor in n‐Type Organic Thermoelectrics

Zuo

Wang

et al. 2017

Adv Elect Materials

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be attributed to the absence of an n-type equivalent of PEDOT, the overall scarcity of n-type OSCs, and the inefficiency of most n-type dopants. Since most good OSCs that are used as n-type materials like [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) and N2200 have a lowest unoccupied molecular orbital (LUMO) around −4.0 eV, [7,8] it is very difficult to realize a stable dopant with a HOMO above −4.0 eV as would be required for efficient electron transfer. Fortunately, Wei et al. have reported a promising material, (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl) dimethylamine (N-DMBI), that can be used as stable n-type dopant due to a two-step thermally activated doping mechanism. [9] Very recently, Huang et al. used this dopant to achieve record values for PF = 105 µW m −1 K −2 and ZT = 0.11 at room temperature for the small molecule A-DCV-DPPTT. [10] Some reports also have demonstrated that dihydro-1H-benzoimidazol-2-yl (N-DBI) derivatives can improve the electrical conductivity by several orders of magnitude in n-type OTE by solution-processing. For example, Schlitz et al. have shown that solution mixtures of P(NDIOD-T2) with 9 mol% N-DBI derivatives can achieve σ ≈ 1 S m −1 and a PF over 0.6 µW m −1 K −2 . [11] Yuan et al. reported a small-molecule 2DQTT-o-OD that, with 10 wt% of a novel N-DBI derivative incorporated in solution, acquires a PF of 17.2 µW m −1 K −2 at room temperature. [12] Shi et al. achieved a high electron mobility in FBDPPV with σ ≈ 1400 S m −1 and PF ≈ 28 µW m −1 K −2 , when adding around 5 wt% N-DMBI in solution. [13] Despite the positive effect of N-DMBI and N-DBI derivatives on electrical conductivity, it probably fails to further increase σ and PF upon further increasing the volume fraction in solution mixtures due to degradation of the blend morphology. [14] Liu et al. demonstrated a modified fullerene derivative, PTEG-1, that shows an increased miscibility at the nanoscale level and thereby achieved a PF of 16.7 µW m −1 K −2 with σ ≈ 205 S m −1 at 40 mol% of N-DMBI. [15] For p-type OTE, most reported experimental data seem to follow an empirical quasi-universal power law relationship between the Seebeck coefficient S and conductivity as S ∝ σ − 1/4 . [2,3] In view of the limited number of reported data, it is still unclear whether n-type OTE also follow this power law, and different power law slopes have been reported. [15,16] Here, we introduce a novel, inverse-sequential doping procedure that mitigates the need for solvent orthogonality in conventional sequential doping to investigate the potential of deposited on a previously cast dopant 4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)-N,N-diphenylaniline film to achieve a very high power factor PF ≈ 35 µW m −1 K −2 with a conductivity σ ≈ 40 S m −1 is introduced. It is also shown that n-type organic semiconductors obey the −1/4 power law relation between Seebeck coefficient S and σ that are previously found for p-type materials. An analytical model on basis of variable range hopping unifies these results. Th...

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“…From equation , it is clear that both the electrical conductivity and the Seebeck coefficient are closely related to the DOS distribution. Recently, Kemerink et al, broadened the DOS distribution by mixing two donor polymers in order to obtain very high Seebeck coefficients (of over 1 mV K −1 ) at the expense of electrical conductivity . To the best of our knowledge, none of the previous works focused on improving the n‐type OTE from a perspective of DOS.…”

Section: Thermoelectric Properties Of Solution‐processed N‐type Conjumentioning

confidence: 99%

N‐Type Organic Thermoelectrics of Donor–Acceptor Copolymers: Improved Power Factor by Molecular Tailoring of the Density of States

et al. 2018

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It is demonstrated that the n-type thermoelectric performance of donor-acceptor (D-A) copolymers can be enhanced by a factor of >1000 by tailoring the density of states (DOS). The DOS distribution is tailored by embedding sp -nitrogen atoms into the donor moiety of the D-A backbone. Consequently, an electrical conductivity of 1.8 S cm and a power factor of 4.5 µW m K are achieved. Interestingly, an unusual sign switching (from negative to positive) of the Seebeck coefficient of the unmodified D-A copolymer at moderately high dopant loading is observed. A direct measurement of the DOS shows that the DOS distributions become less broad upon modifying the backbone in both pristine and doped states. Additionally, doping-induced charge transfer complexes (CTC) states, which are energetically located below the neutral band, are observed in DOS of the doped unmodified D-A copolymer. It is proposed that charge transport through these CTC states is responsible for the positive Seebeck coefficients in this n-doped system. This is supported by numerical simulation and temperature dependence of Seebeck coefficient. The work provides a unique insight into the fundamental understanding of molecular doping and sheds light on designing efficient n-type OTE materials from a perspective of tailoring the DOS.

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High Seebeck Coefficient in Mixtures of Conjugated Polymers

Cited by 91 publications

References 23 publications

Self‐Healable and Stretchable Organic Thermoelectric Materials: Electrically Percolated Polymer Nanowires Embedded in Thermoplastic Elastomer Matrix

Self‐Healable and Stretchable Organic Thermoelectric Materials: Electrically Percolated Polymer Nanowires Embedded in Thermoplastic Elastomer Matrix

High Seebeck Coefficient and Power Factor in n‐Type Organic Thermoelectrics

N‐Type Organic Thermoelectrics of Donor–Acceptor Copolymers: Improved Power Factor by Molecular Tailoring of the Density of States

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