Principles of Structural Design of Conjugated Polymers Showing Excellent Charge Transport toward Thermoelectrics and Bioelectronics Applications

Abstract

Conjugated polymers, especially their second generation with a donor–acceptor alternating structure, have promising properties. These are suitable for two emerging fields, thermoelectrics and bioelectronics, if appropriate structural designs are implemented. This review aims to give a perspective for the potential and challenges of novel conjugated polymers in such applications. In particular, the aspects of synthetic design and the consequences of modifications of the chemical structure on the charge transport in selected second‐generation conjugated polymers are reviewed. By understanding the effects of structural motifs on the overall material properties, polymers can be specifically tailored for the respective application. The basics of charge transport measurements are briefly summarized, as the charge transport plays an important role for thermoelectrics as well as for bioelectronics. In particular, the correlation between the reported charge carrier mobility values and the structural design of the polymers is reviewed. Examples of the application of second‐generation conducting polymers in thermoelectrics and bioelectronics are shown to demonstrate the current state of research. Finally, the prospect of a purposeful design of new materials for these two emerging fields is discussed.

Mixed Conduction in an N‐Type Organic Semiconductor in the Absence of Hydrophilic Side‐Chains

“…The latter necessitates high electrochemical biases to populate a sufficient number of carriers in the lowest unoccupied molecular orbital (LUMO). However, the electrochemical window of water (<1 V) limits the extent to which CPs can be biased before they suffer from harmful electrochemical side products, restricting the operating range [16,17,21,22] Synthesis of n-types with LUMOs deeper than −4 eV mitigates stability issues in ambient environment, [21,23,24] yet the design of such materials remains extremely challenging.…”

The Key Role of Side Chain Linkage in Structure Formation and Mixed Conduction of Ethylene Glycol Substituted Polythiophenes

“…10 In general, the mixed conductors are attractive materials for several applications, such as thermoelectric devices, electrochromic displays and bioelectronics. 8,9,11,12 The widely studied class of p-type semiconductors for bioelectronics still comprises of polythiophene derivatives, due to their high crystallinity, excellent charge carrier properties, high solubility and the feasibility of a controlled synthesis. The synthesis of substituted polythiophenes is of exceptional character, due to the quasi living polymerization character of the Kumada catalyst transfer polymerization, which was initially developed for poly-3-hexylthiophene (P3HT).…”

Polydiketopyrrolopyrroles Carrying Ethylene Glycol Substituents as Efficient Mixed Ion‐Electron Conductors for Biocompatible Organic Electrochemical Transistors

“…Conjugated polymers have become ubiquitous in many kinds of electronic applications, such as light emitting diodes, [ 1,2 ] solar cells, [ 3–5 ] field effect transistors, [ 6 ] and thermoelectrics, [ 7–10 ] and naturally they also found their way into the field of organic bioelectronics. [ 11 ] In bioelectronic devices, mixed ion‐electron conductors (MIECs) are required as the active materials to transport both electrical charges and ions.…”