Organic Thermoelectric Materials from n‐Type Polymer Semiconductors

Abstract

Organic thermoelectric (OTE) materials have garnered increasing attention due to their potential application in wearable/ flexible TE generator for energy harvesting. To meet the practical application of thermoelectric device, high-performance p-and n-type OTE materials are both necessary. In the past few years, improved n-type polymer semiconductors have developed rapidly in the OTE field; however, their thermoelectric performance is still lagging behind p-type counterparts. Therefore, more efforts should be made to enhance n-type polymer TE performance, including development of novel molecule structure, synthesis of new dopants and optimization of device engineering. In this Review, we highlight the effects of molecular structure and side chain length and polarity of n-type polymer semiconductors on the TE performance such as electron transport, electrical conductivity, and power factor. Finally, further perspectives and challenges are also discussed to provide useful guidelines for the design of high-performance n-type OTE materials.

Effect of a benzothiadiazole spacer on transport properties and N-doping of naphthalene-diimide-based copolymers

“…It corroborates with the higher mobility observed for undoped films in OFET. While the achieved conductivity values may not reach the level of the highest performing thermoelectric materials, 11,15 we have successfully demonstrated an enhancement in conductivity using N-DMBI without the requirement of post-deposition thermal annealing. Avoiding post-deposition annealing is particularly interesting for polymer films deposited on flexible substrates being more sensitive to high temperature.…”

“…Among these classes of electron deficient moieties, naphthalene diimide (commonly abbreviated to NDI) is probably the most studied. 14,15 Aromatic diimide species are known to undergo two reversible one-electron reductions. 16 The resulting anions and dianions are indeed stabilised by a mesomeric effect.…”

“…24 There is a plethora of n-type materials based on NDI or BTD in the literature, but the combination of these two electron-deficient units within a single structure has rarely been explored. 15,21,22 Although there are examples of polymers combining these two units, the effects of introducing the BTD unit as a third co-monomer on the transport properties and, in particular, the doping mechanisms of these materials have not been elucidated. In this study, we report on the synthesis of two NDI-based polymers, one of which contains a BTD unit, and we investigate in detail their optoelectronic and transport properties.…”

Dimensionality-Dependent Electronic Properties of the Highly Conducting n-Type Polymer, Poly(benzodifurandione)

“…Following a tandem polymerization/reductive doping process, the backbone ends up carrying excess negative charges (nearly 0.9 excess electron per BDF unit), with protons serving as counterions. n-PBDF displays the highest n-type electrical conductivity measured to date, up to 6000 S/cm. , Also, n-PBDF has been shown to exhibit both kinetic and thermodynamic stabilities, which makes it a promising candidate across a diverse range of applications, from electrochemical transistors to thermoelectric devices and transparent conducting electrodes. − These advances have stimulated considerable interest in the realm of organic electronics − and call for a comprehensive understanding of the electronic properties of this polymer.…”