A general relationship between disorder, aggregation and charge transport in conjugated polymers

Abstract

Conjugated polymer chains have many degrees of conformational freedom and interact weakly with each other, resulting in complex microstructures in the solid state. Understanding charge transport in such systems, which have amorphous and ordered phases exhibiting varying degrees of order, has proved difficult owing to the contribution of electronic processes at various length scales. The growing technological appeal of these semiconductors makes such fundamental knowledge extremely important for materials and process design. We propose a unified model of how charge carriers travel in conjugated polymer films. We show that in high-molecular-weight semiconducting polymers the limiting charge transport step is trapping caused by lattice disorder, and that short-range intermolecular aggregation is sufficient for efficient long-range charge transport. This generalization explains the seemingly contradicting high performance of recently reported, poorly ordered polymers and suggests molecular design strategies to further improve the performance of future generations of organic electronic materials.

Developing accurate molecular mechanics force fields for conjugated molecular systems

“…70 For many amorphous polymers molecular simulations are the main tools to formulate hypotheses on the microscopic structure 3-7 and these are severely limited (among other things) by the lack of reliable force fields for the ever-increasing number of oligomers used. Thus, in this section we report the FF parameters for a DPP based polymer TT-DPP (Figures 6) constructed using our FM approach.…”

π-Conjugated polymer-layered structures: synthesis and self-assembly

“…[3][4][5][6][7][8][9][10][11] Because π-conjugated compounds tend to aggregate by π-π stacking, the introduction of non-covalent interactions at appropriate positions increases their association constants and facilitates the formation of higher-ordered structures. 12,13 For example, supramolecular gels can be formed through intermolecular interactions such as hydrogen bonds, 14,15 and multiple long alkyl chains facilitate columnar stacking along the π-stacking direction of supramolecular assemblies [16][17][18][19] (Figure 1a).…”

Recent Advances in Polymer Organic Light-Emitting Diodes (PLED) Using Non-conjugated Polymers as the Emitting Layer and Contrasting Them with Conjugated Counterparts

“…32 Conjugated polymers with higher molecular weight are shown to have better charge mobility because long polymer chains serve as interconnections between ordered phases of the polymer film. 124 In addition, high-molecular-weight alternating copolymer of fluorene and MeH-PPV showed a much higher U PL of 61.2% than the low molecular weight analogue (U PL : 26.8%) whose short polymer chains were more rod-like, which resulted in more pronounced p-p stacking and hence greater energy transfer to the quenching site. 123 Under certain circumstances, a high-molecularweight polymer is not necessarily superior to a low-molecular-weight one, but workers can make a wise use of their different physical properties.…”