Charge transport in high-mobility conjugated polymers and molecular semiconductors

Abstract

Conjugated polymers and molecular semiconductors are emerging as a viable semiconductor technology in industries such as displays, electronics, renewable energy, sensing and healthcare. A key enabling factor has been significant scientific progress in improving their charge transport properties and carrier mobilities, which has been made possible by a better understanding of the molecular structure-property relationships and the underpinning charge transport physics. Here we aim to present a coherent review of how we understand charge transport in these high-mobility van der Waals bonded semiconductors. Specific questions of interest include estimates for intrinsic limits to the carrier mobilities that might ultimately be achievable; a discussion of the coupling between charge and structural dynamics; the importance of molecular conformations and mesoscale structural features; how the transport physics of conjugated polymers and small molecule semiconductors are related; and how the incorporation of counterions in doped films-as used, for example, in bioelectronics and thermoelectric devices-affects the electronic structure and charge transport properties.

Ion Coordination and Chelation in a Glycolated Polymer Semiconductor: Molecular Dynamics and X-ray Fluorescence Study

“…At the heart of OECTs working principle is the active material, which is usually a π-conjugated polymer or polymer blend able to host or be chemically linked to charged groups. 10 The greatest challenges of developing organic mixed ionic-electronic conductors (OMIECs) is the need to optimize the seemingly contrasting processes of electronic and ionic charge transport: while the factors governing electronic charge transport in conjugated polymers is now fairly well understood, [11][12][13] little is known about how the presence of water and ions affects both the microstructure of the materials and its transport characteristics. On the other hand, although ion transport has been extensively studied in the context of capacitors and batteries, where it is one of the main governing processes, a systematic understanding of ion percolation in OMIECs is still in its infancy and limited to a few widespread materials.…”

Flickering Polarons Extending over Ten Nanometres Mediate Charge Transport in High‐Mobility Organic Crystals

“…It is now well established that the weak molecular interactions between the molecules of OSs give rise to slow intermolecular vibrations [6][7][8] that strongly impact charge carrier mobility and device performance. This (dynamical) disorder also places charge transport in a difficult regime where the relevant transport parameters (electronic coupling, reorganization energy, site energy and electronic coupling fluctuations, and thermal energy) are all on the same energy scale, typically 10-200 meV.…”

“…The theory was successfully used to show that charge transport in the high mobility planes of typical singlecrystalline OSs is enhanced if electronic couplings between the molecules within the plane are isotropic and are of specific sign combinations. [7,26,27] TLT has also recently been connected to the standard band transport description in the case of small disorder. [28] Yet, we note that TLT does not give information on how the charge carrier moves across the material in real time due to the assumptions of this theory with regards to the dynamics.…”

Organic Bioelectronics: From Functional Materials to Next‐Generation Devices and Power Sources

“…[45,56] The localization of charges limits the electronic conductivity of polymers, typically giving rise to traps in the presence of high disorder or in the absence of connectivity between the segments within the complex polymer microstructure. [56] A semiconducting polymer can become conducting (i.e., charged or doped) i) chemically, by exposing the polymer to a reducing or oxidizing solution that contains dopant acceptor or donor molecules, or ii) upon application of an electric field to the film interfacing an electrolyte that contains ionic species which electrostatically compensate for the electronic charges that are injected from a metal contact. [45,57] For bioelectronic devices where the CP film has an interface with an electrolyte, the latter summarizes the operation principle.…”