Efficient Charge Transport in Disordered Conjugated Polymer Microstructures

Abstract

A new class of conjugated polymers with high charge mobilities exhibits the apparently conflicting morphological features of increased order at the molecular scale while lacking long-range order and crystallinity. To exploit their unique properties, mechanistic insights for charge transport events taking place from the molecular to the device scale must be uncovered. Thus, a central contributor to the continued progress in conjugated optoelectronic materials will be the development of advanced characterization tools, particularly those targeted to measuring the charge-transfer processes in heterogeneous, anisotropic, and hierarchically structured materials. This feature article describes the morphological properties that make partially ordered polymers an intriguing materials system to explore connections between chemical identity, solid-phase microstructure, and hierarchical charge transport. To this end, recent directions in materials development and new opportunities for characterization are discussed.

The Polymer Physics of Multiscale Charge Transport in Conjugated Systems

“…At lengths comparable to the size of polymer aggregates or crystallites (typically 10's of nanometer), charge transport is dictated by interchain electronic coupling and requires multiple interchain hopping events, which is typically two or three orders of magnitude slower than intrachain charge transport. At longer yet length scales (above 100's of nanometer; typical transistor channel lengths are well above 1 μm), macroscopic charge transport is limited by transport in the amorphous regions where π‐stacking is disrupted, unless the ordered domains are sufficiently connected, in which case charge transport is then limited by the interchain hopping within the ordered regions …”

“…At longer yet length scales (above 100's of nanometer; typical transistor channel lengths are well above 1 μm), macroscopic charge transport is limited by transport in the amorphous regions where π-stacking is disrupted, unless the ordered domains are sufficiently connected, in which case charge transport is then limited by the interchain hopping within the ordered regions. 29,34,35 Bridging the gaps in our knowledge about microstructures across length scales and our interest in macroscopic charge transport and, ultimately device performance, will facilitate the deployment of morphologically heterogeneous conjugated polymers in large-scale opto-electronic applications. 15,36,37 FIGURE 2 Cartoon representation of typical microstructure of conjugated polymers.…”

Transport models in disordered organic semiconductors and their application to the simulation of thin‐film transistors

“…The MTR model was even claimed to model the transport properties of very high mobility polymers (up to 10 cm 2 V −1 s −1 ) . To explain the high mobilities, Noriega et al . argued that ordered and disordered regions coexist in these polymers.…”

“…The MTR model was even claimed to model the transport properties of very high mobility polymers (up to 10 cm 2 V −1 s −1 ). 42,44 To explain the high mobilities, Noriega et al 42,45 argued that ordered and disordered regions coexist in these polymers. Those authors explain the high mobility by the ability of some molecules to connect ordered regions between them like a wire.…”

Unexpectedly Large Couplings Between Orthogonal Units in Anthraquinone Polymers

“…The latter propertyi s essential for efficient charge transporta long the polymer chain, which is one of the main factors that determines bulk mobility. [7][8][9] Due to the nature of p orbitals, conjugation across monomers is optimal when they are coplanar. [1,3,10] Thec hargetransfer integral (electronic coupling) between neighboring monomers depends on the intermonomert orsion (dihedral angle) and decreases if the geometry deviates from planarity.…”