Systematic Power Factor Enhancement in n‐Type NiETT/PVDF Composite Films

Menon, Akanksha K.; Wolfe, Rylan M. W.; Marder, Seth R.; Reynolds, John R.; Yee, Shannon K.

doi:10.1002/adfm.201801620

Cited by 35 publications

(45 citation statements)

References 23 publications

(36 reference statements)

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“…This indicates the need for studying NiETTs further, and developing an n‐type material that is both highly performing and solution processable. We have recently reported an optimized synthesis of Na[NiETT] that provides a reproducible material as validated by elemental analysis, X‐ray photoelectron spectroscopy, and consistent TE properties across batches . In that study, it was observed that thermal annealing composite films of ETT with PVDF/DMSO at ambient pressure resulted in a simultaneous increase in σ and S , thereby yielding power factors over 20 µW m −1 K −2 ; this represents a significant improvement (50 ×) over previous reports which had a power factor of 0.4 µW m −1 K −2 for these same blends .…”

Section: Introductionmentioning

confidence: 67%

“…This work investigates the use of an annealing post‐treatment process to enhance the performance of NiETT/PVDF thin films cast from DMSO. While we previously demonstrated the reproducibility between batches and batch sizes, nonetheless a single batch of Na(NiETT) was selected for all annealing studies to remove any possible differences in particle size or composition. The TE properties were simultaneously enhanced upon annealing composite films, and are attributed to i) improved film morphology and ii) compositional changes in the NiETT material.…”

Section: Resultsmentioning

confidence: 99%

“…Polymer Synthesis : A single batch of Na[Ni(ETT)], prepared according to our recent literature procedure, was used for all experiments . In a cool, dry roundbottom flask with magnetic stir bar, thiapendione (500 mg, 2.4 mmol, 1.0 equiv) was added against a positive flow of argon.…”

Section: Methodsmentioning

confidence: 99%

“…The source of this signal is potentially from unreacted carbonyl end groups or sulfonyl irregularities in the polymer backbone. Previous elemental analyses and X‐ray photoelectron spectroscopy (XPS) data support the presence of such impurities . Even in carefully controlled syntheses, impurities and deviations from the idealized structure are present and should be expected.…”

Section: Annealing Enhances Thermoelectric Propertiesmentioning

confidence: 99%

“…We refer the reader to our previous work on ETT optimization to obtain details on the synthesis parameters and reaction conditions (or see Experimental Section) . At the end of the synthesis, the reaction solution is vacuum filtered and the insoluble product dried under vacuum at room temperature for 24 hours to obtain NiETT particles in the form of a blue‐gray lustrous powder (elemental analyses are given in Table S1, Supporting Information).…”

Section: Annealing Enhances Thermoelectric Propertiesmentioning

confidence: 99%

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Simultaneous Enhancement in Electrical Conductivity and Thermopower of n‐Type NiETT/PVDF Composite Films by Annealing

Wolfe

Menon

Fletcher³

et al. 2018

Adv Funct Materials

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Nickel ethenetetrathiolate (NiETT) polymers are promising n-type thermoelectric (TE) materials, but their insolubility requires the use of an inert polymer matrix to form films, which is detrimental to the TE performance. In this work, the use of thermal annealing as a post-treatment process simultaneously enhances the electrical conductivity from 6 ± 2 to 23 ± 3 S cm −1 and thermopower from −28 ± 3 to −74 ± 4 µV K −1 for NiETT/PVDF composite films. Spectroscopic characterization reveals that the underlying mechanism involves removal of residual solvent and volatile impurities (carbonyl sulfide and water) in the NiETT polymer backbone. Additionally, microscopic characterization reveals morphological changes caused by a densification of the film that improves chain packing. These effects result in a 25 × improvement in power factor from 0.5 to 12.5 µW m −1 K −2 for NiETT/PVDF films and provide insight into the composition of these coordination polymers that maintain their stability under ambient conditions.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201803275.techniques. There has been considerable effort recently in the area of organic TEs; however, much of this has focused on derivatives of poly(3,4-ethylenedioxythiophene) [1][2][3][4] that have high electrical conductivities, σ, but often suffer from a low Seebeck coefficient or thermopower, S. In contrast, organic n-type materials tend to have high S and low σ values, [5][6][7] necessitating the use of doping, which often drastically reduces the thermopower and can render the materials air sensitive. These results illustrate the inherent inverse correlation between these TE properties, and these trade-offs have been well studied in inorganic TE materials [8] within the framework of band-like transport. [9] Polymers, however, are unique in that the material performance is strongly determined by the processing conditions that impact film morphology, [10,11] and transport is better described by thermally activated hopping conduction. [3,12,13] Metal-coordination compounds, specifically metal-dithiolene coordination polymers, consisting of bridging ethenetetrathiolate ligands and nickel metal centers (nickel ethenetetrathiolate, NiETT), are one of the best-performing n-type organic TE materials. Pressed pellets of poly[K(NiETT)] have demonstrated high TE properties with S = −120 µV K −1 and σ = 44 S cm −1 at room temperature, but the insoluble nature of the material limits its applicability. [14] One route to make NiETTs solution processable is by blending it with an inert matrix ( e.g., poly(vinylidene fluoride), PVDF) and casting from low vapor pressure solvents (e.g.. dimethyl sulfoxide, DMSO) albeit at the sacrifice of electrical conductivity. [15] Other strategies include fabricating composites with carbon nanotubes that yield high power factors, but the resulting material is often p-type. [16,17] This indicates the need for studying NiETTs further, and developing an n-type material that...

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Section: Introductionmentioning

confidence: 67%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Annealing Enhances Thermoelectric Propertiesmentioning

confidence: 99%

Section: Annealing Enhances Thermoelectric Propertiesmentioning

confidence: 99%

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