Understanding morphology-mobility dependence in PEDOT:Tos

Abstract

The potential of conjugated polymers to compete with inorganic materials in the field of semiconductor is conditional on fine-tuning of the charge carriers mobility. The latter is closely related to the material morphology, and various studies have shown that the bottleneck for charge transport is the connectivity between well-ordered crystallites, with a high degree of π -π stacking, dispersed into a disordered matrix. However, at this time there is a lack of theoretical descriptions accounting for this link between morphology and mobility, hindering the development of systematic material designs. Here we propose a computational model to predict charge carriers mobility in conducting polymer PEDOT depending on the physicochemical properties of the system. We start by calculating the morphology using molecular dynamics simulations. Based on the calculated morphology we perform quantum mechanical calculation of the transfer integrals between states in polymer chains and calculate corresponding hopping rates using the Miller-Abrahams formalism. We then construct a transport resistive network, calculate the mobility using a mean-field approach, and analyze the calculated mobility in terms of transfer integrals distributions and percolation thresholds. Our results provide theoretical support for the recent study [Noriega et al., Nat. Mater. 12, 1038] explaining why the mobility in polymers rapidly increases as the chain length is increased and then saturates for sufficiently long chains. Our study also provides the answer to the long-standing question whether the enhancement of the crystallinity is the key to designing high-mobility polymers. We demonstrate, that it is the effective π -π stacking, not the long-range order that is essential for the material design for the enhanced electrical performance. This generic model can compare the mobility of a polymer thin film with different solvent contents, solvent additives, dopant species or polymer characteristics, providing a general framework to design new high mobility conjugated polymer materials.

Morphology and ion diffusion in PEDOT:Tos. A coarse grained molecular dynamics simulation

“…The ionic and electronic transport properties of PEDOT:Tos are strongly related to and determined by its complex morphology. 26 There are extensive experimental efforts to understand the morphology of PEDOT films. [2][3][4]27 At the same time, theoretical work addressing the morphology of PEDOT:PSS is practically missing.…”

Computational microscopy study of the granular structure and pH dependence of PEDOT:PSS

“…1(d 62 The conflicting reports on the morphological picture of PEDOT:PSS mentioned above can be attributed in part to a lack of theoretical understanding of its complex morphology. Note that various aspects of morphology and transport in PEDOT doped with molecular counterions (as opposed to PSS, which is a poly-anion) were recently studied by the present authors using all atomistic and coarse-grained molecular dynamics simulations (CG MD), addressing the effect of crystallite formation, 63 the chain length, 62 various counterions and oxidation levels, 18 ion diffusion, 64 and the effect of the substrate on the morphology and conductivity. 65 At the same time, theoretical studies of realistic PEDOT:PSS capturing the essential features of the PEDOT: PSS morphology such as p-p stacking and granular structure formation are practically missing.…”

“…At the same time, coarse grained approaches should be sufficiently detailed to be able to reproduce the p-p stacking and crystallite formation, which is essential for the formation of the percolative conductance paths through PEDOT. 62 (It should be noted that several all-atomistic MD studies of PEDOT:PSS have been reported recently. [66][67][68] They however did not address the morphological features discussed above such as p-p stacking formation and granular structure of PEDOT:PSS.…”

Recent advances in ion sensing with conducting polymers

“…Given the apparent link between the polymer structure and the resultant properties, Rolland et al [76] undertook a theoretical study to link the morphology and charge carrier mobility for poly(3,4-ethylenedioxythiophene) doped with tosylate. Central to this study was determining whether crystallinity was a sufficient enough criterion for good charge transport within the conducting polymer.…”