Confinement highlights the different electrical transport mechanisms prevailing in conducting polymers

Sukanya Das, Anil Kumar, and K. S. Narayan

Phys. Rev. Materials 6, 025602 – Published 8 February 2022

Abstract

We study the differences in electrical charge transport dynamics of the conductivity enhancement of poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives under geometrical confinement. The results of polymer blend poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and a polymer-monomer blend, poly(3,4-ethylenedioxythiophene):tosylate, highlight the role of dopants and processing conditions of these systems under confinement. The prevailing transport length scales in confined geometry of characteristic dimensions originate from varying disorder in these polymer systems. These observable differences in two different PEDOTs introduced by molecular level reorganization can be utilized to tune conducting polymer systems for efficient electrical and thermoelectric properties. The electrical conductivity σ of the polymer system, which is a function of the electronic structure at molecular level and a connectivity parameter, has been probed in cylindrical-alumina nanoscaffolds of various channel diameters, at different frequencies ω and temperatures $T$ . The observations also emphasize the role of disorder in these conducting polymer systems.

Received 11 November 2020
Revised 19 December 2021
Accepted 18 January 2022

DOI:https://doi.org/10.1103/PhysRevMaterials.6.025602

Physics Subject Headings (PhySH)

Confinement Fluctuations & noise Organic electronics Polymer behavior

Polymers & Soft Matter

Authors & Affiliations

Sukanya Das ¹, Anil Kumar², and K. S. Narayan^1,*

¹Chemistry and Physics of Materials Unit and School of Advanced Materials, Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru 560064, India
²Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India

^*narayan@jncasr.ac.in

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Vol. 6, Iss. 2 — February 2022

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Images

Figure 1
Dc conduction of PEDOT:Tos: (a) Lateral dc conductivity, $σ_{lateral}$ of PEDOT:Tos films (of thickness 200 nm) for three different configurations of electrode contact on the film with four-probe method on a glass substrate with patterned ITO as bottom electrodes, thermally evaporated bottom Au electrodes, and Au as top electrodes. (b) $σ_{transverse}$ of PEDOT:Tos nanochannels between bottom ITO and top Au electrodes versus polymer filled alumina-nanochannel diameters. Temperature-dependent transverse dc conduction: (c) σ( $T$ ) of PEDOT:Tos and PEDOT:PSS nanochannels in the temperature range $10 K < T < 340 K$ for different channel dimensions and (d) $σ_{T} / σ_{300 K} (T)$ (with $y$ axis in log scale) for all PEDOT:Tos and PEDOT:PSS channels; inset shows $σ_{T} / σ_{300 K} (T)$ in linear $y$ axis for PEDOT:Tos nanochannel diameters with indication line of the transition temperature $T_{M}$ .
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Figure 2
Single nanochannel transport. (a) Surface morphology of PEDOT:Tos filled 50 nm AAO surface, a section of which is partially removed as indicated by a dotted square region. The resultant cross-sectional image of the interface shows the exposed PEDOT nanopillars, a few of which have color added as a guide. Partial removal of top PEDOT filled AAO surface shows evidence of PEDOT filling through the length of the channels: (b), (d) represents topography and phase, respectively, of the dotted square region which comprises exposed bare alumina and PEDOT filled nanochannels. The alternate bare AAO and PEDOT channels are also shown in the line scan of surface roughness (f) marked in brown. Line scan of surface roughness (f) marked in orange shows a minimum (top concave meniscus of PEDOT adhering to inner surface of nanocylinder formed on annealing) corresponding to each maximum of PEDOT (resultant convex meniscus of PEDOT formed midway of a nanocylinder due to peeling of top PEDOT film) in other line scan marked in brown. (c), (e) are the respective topography and phase images of the top surface of PEDOT filled 50 nm channels. Noncontact mode AFM imaging showing (g), (i) topography and (h), (j) phase across a 20 nm PEDOT:Tos AAO/ITO interface over a scan area of 1.2 μm × 1.8 μm and on a PEDOT:Tos filled 20 nm AAO surface over a scan area of 700 nm × 700 nm, respectively. Conductive AFM in contact mode showing (k) topography and (l) current profile of 80 nm PEDOT:Tos nanochannels.
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Figure 3
Ac conduction in (a) 20 nm and (b) 100 nm PEDOT:Tos channels for temperature range $80 K < T < 340 K$ . (c) represents the σ(ω, $T$ ) behavior for two polymer blends in 20 nm channels: $σ_{PEDOT : PSS}$ shows a wide dispersion over ω and $T$ scales in comparison to precisely unchanged $σ_{PEDOT : Tos}$ . (d) Normalized ac conductivity, $σ_{norm}$ of two polymer blends, PEDOT:PSS (increasingly dark shades of brown in accordance to increasing $T$ scales), and PEDOT:Tos (marked in blue); inset shows the onset frequency $ω_{0} (T)$ for PEDOT:PSS and PEDOT:Tos in the range $80 K < T < 340 K$ .
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Figure 4
Noise studies, $S_{I} (ω) / I^{2}$ in (a) 20 nm PEDOT:PSS nanochannels, and (b) 20 nm PEDOT:Tos nanochannels over a temperature range of $153 K < T < 340 K$ , respectively. Insets of (a), (b) show the respective normalized PSD with bias conditions. (c) Corner frequency $f_{c}$ versus $T$ for PEDOT:PSS and PEDOT:Tos channel dimensions. (d) Hooge's exponent, γ with different bias conditions at max $T ↑ = 340 K$ (red) and min $T ↓ = 153 K$ (blue) as parameters for 20, 50, and 100 nm PEDOT:PSS nanochannels, respectively.
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