Substrate-Dependent Morphology and Its Effect on Electrical Mobility of Doped Poly(3,4-ethylenedioxythiophene) (PEDOT) Thin Films

Abstract

Deposition dynamics, crystallization, molecular packing, and electronic mobility of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films are affected by the nature of the substrate. Computational microscopy has been carried out to reveal the morphology-substrate dependence for PEDOT thin films doped with molecular tosylate deposited on different substrates including graphite, SiN, silicon, and amorphous SiO. It is shown that the substrate is instrumental in formation of the lamellar structure. PEDOT films on the ordered substrates (graphite, SiN, and silicon) exhibit preferential face-on orientation, with graphite showing the most ordered and pronounced face-on packing. In contrast, PEDOT on amorphous SiO exhibits the dominant edge-on orientation, except in the dry state where both packings are equally presented. The role of water and the porosity of the substrate in formation of the edge-on structure on SiO is outlined. On the basis of the calculated morphology, the multiscale calculations of the electronic transport and percolative analysis are performed outlining how the character of the substrate affects the electron mobility. It is demonstrated that good crystallinity (PEDOT on graphite substrate) and high content of edge-on (PEDOT on SiO substrate) are not enough to achieve the highest electrical in-plane mobility. Instead, the least ordered material with lower degree of the edge-on content (PEDOT on silicon substrate) provides the highest mobility because it exhibits an efficient network of π-π stacked chain extending throughout the entire sample.

The intrinsic volumetric capacitance of conducting polymers: pseudo-capacitors or double-layer supercapacitors?

“…For the choice of a counterion we follow previous computational studies of thiophene-based polymers 57 and use Cl À 3 , which is motivated by the computational efficiency as compared to the case of larger counterions such as tosylate. It is important to stress that results and conclusions presented in this paper are not related to a particular choice of counterions: our previous studies of the effect of different counterions shows that neither chemical bonds form nor electron transfer takes place for the case of other counterions such as tosylate, ClO 4 56,58 The results of the molecular dynamics simulations [52][53][54][55][56] are used as a guidance to distribute counterions around polymer chains and crystallites. In particular, the counterions are positioned randomly on the average distance of 4 A from the polymer chains as suggested by the distribution functions obtained from the MD simulations (see e.g.…”

“…[48][49][50][51] These ndings are also conrmed by molecular dynamics simulations. [52][53][54][55][56] We calculate the total energy of the system, E(N), using the DFT approach. Because of the computation limitations of the DFT approach we apparently cannot consider a system of size even comparable to a dimension of the polymeric thin lm (10-100 nm).…”

Reversible Electronic Solid–Gel Switching of a Conjugated Polymer

“…Note that the GAFF was successfully used for description of many morphological features experimentally observed in π-conjugated conducting polymers including the π-π stacking among the polymer chains, a crystallite size, a lamellar structure formation, effect of the substrate, and many others. [28][29][30] Bonds and angles of water are constrained by SHAKE algorithm. [31] The chain length of 20 repeating monomer units was taken where the triethylene glycol sidechains were connected to the alternate thiophene ring.…”

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

“…This way to reach the final dry film from the initial solution corresponds to the experimental procedure used by Palumbiny at al., 44 and was utilized in our previous studies. 18,[63][64][65]73 During evaporation we fix the x-and y-dimensions of the simulation box to mimic the drop-casting process used in the experimental fabrication of polymer thin films. The final size of the computational box is 30 nm  30 nm  5 nm for a dry film at Hy = 10%, see Fig.…”

“…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. This is remarkable, taking into account the fact that the number of experimental papers on PEDOT:PSS far exceeds 1000 per year and is growing.…”