Thermoelectric Performance of n‐Type Poly(Ni‐tetrathiooxalate) as a Counterpart to Poly(Ni‐ethenetetrathiolate): NiTTO versus NiETT

Abstract

The synthesis of the metal-coordination polymer poly(nickel tetrathiooxalate) (NiTTO) is presented, which represents an alternative route to n-type thermoelectric materials similar in nature to nickel ethenetetrathiolate (NiETT) polymers. The TTO monomer is synthesized through an electrochemical reduction of carbon disulfide, followed by coordination polymerization with a nickel(II) salt to yield a coordination complex polymer with a neutral repeat unit. An alkali metal counterion exchange and polymerization optimization are performed, and a thermoelectric power factor of 6 µW/m-K 2 (electrical conductivity of over 10 S/cm) is achieved for NiTTO-PVDF composite films. This is significantly higher than other reported n-type polymers (and to within a factor of two of NiETT) and demonstrates the potential of NiTTO as a new thermoelectric material. Elemental analysis indicates a nearly neutral backbone structure in NiTTO with minimal charge balancing alkali ions, indicating that these polymers are more oxidized than NiETTs. XPS reveals a different coordination environment for NiTTO compared to NiETTs with the same alkali counterion, indicating that -despite their structural similarity in theory -these two materials are indeed different.

A thermally activated and highly miscible dopant for n-type organic thermoelectrics

“…4a). Air stability in one of the key issues in high-performance n-type thermoelectric materials 49,50 . The TAM-doped FBDPPV thick films are stable in air at room temperature.…”

Sequential Doping of Ladder-Type Conjugated Polymers for Thermally Stable n-Type Organic Conductors

“…Conjugated polymers have attracted a great deal of attention as a class of semiconducting materials that hold promise for the development of a wealth of traditional as well as unconventional low-cost and distributed technologies. − Their versatile chemical synthesis and inexpensive solution processability enable cost-efficient large-scale production of light, flexible, and even biocompatible electronic devices which would otherwise be difficult to realize using traditional inorganic semiconductors. − The electronic and electrical properties of π-conjugated polymers, and thus, the performance of the resulting (opto)­electronic devices, depend strongly on the charge carrier concentration, which can be tuned by the so-called electrical doping . Both p-doping and n-doping are needed to optimize various electronic devices, including organic solar cells, field-effect transistors, and thermoelectric generators. − This is typically achieved via an electron or proton/hydride transfer between the dopant molecule and the polymer backbone, a process that increases the charge carrier density and hence improves the electrical properties . Conjugated polymers and molecular dopant molecules can either be coprocessed using a common solvent or sequentially processed by exposing the polymer film to the dopant vapors − or the dopant dissolved in an orthogonal solvent. , The advantage of sequential doping over coprocessing doping is that the morphology of the doped films remains to a large extent undisturbed, thus yielding electrical conductivities that are superior to those commonly reached with coprocessing methods …”

A Printable Paste Based on a Stable n-Type Poly[Ni-tto] Semiconducting Polymer

“…It is noteworthy that, unlike individual poly[Ni-tto] [9], the composite film does not show noticeable degradation in its TE properties during two months of storage under ambient conditions. It should also be noted that poly [Ni-tto] with different counterions was synthesized earlier [24,25] and very recently by Wolfe et al [26], who obtained poly[Ni-tto] and its composite with PVDF. The authors obtained poly[Ni-tto] with various counterions: Li, Na and K. Nominally, a polymer with K as a counterion should be identical to the polymer we are considering in this paper.…”

“…The authors obtained poly[Ni-tto] with various counterions: Li, Na and K. Nominally, a polymer with K as a counterion should be identical to the polymer we are considering in this paper. However, these compounds have significant differences in terms of the ratio of elements (compare the data from [9] and [26]) and, as a result, different TE properties. The annealed polyK[Ni-tto]/PVDF composite described by Wolfe has an electrical conductivity of about 21 S/cm and a Seebeck coefficient of 60 µV/K.…”