Structural and Dynamic Disorder, Not Ionic Trapping, Controls Charge Transport in Highly Doped Conducting Polymers

Abstract

Doped organic semiconductors are critical to emerging device applications, including thermoelectrics, bioelectronics, and neuromorphic computing devices. It is commonly assumed that low conductivities in these materials result primarily from charge trapping by the Coulomb potentials of the dopant counterions. Here, we present a combined experimental and theoretical study rebutting this belief. Using a newly developed doping technique based on ion exchange, we prepare highly doped films with several counterions of varying size and shape and characterize their carrier density, electrical conductivity, and paracrystalline disorder. In this uniquely large data set composed of several classes of high-mobility conjugated polymers, each doped with at least five different ions, we find electrical conductivity to be strongly correlated with paracrystalline disorder but poorly correlated with ionic size, suggesting that Coulomb traps do not limit transport. A general model for interacting electrons in highly doped polymers is proposed and carefully parametrized against atomistic calculations, enabling the calculation of electrical conductivity within the framework of transient localization theory. Theoretical calculations are in excellent agreement with experimental data, providing insights into the disorder-limited nature of charge transport and suggesting new strategies to further improve conductivities.

Optimizing chain alignment and preserving the pristine structure of single-ether based PBTTT helps improve thermoelectric properties in sequentially doped thin films

“…Overall, these conclusions are in line with the recent work of Jacobs et al on the influence of para -crystallinity measured in the π-stacking direction on the charge transport properties in doped polymer semiconductors. 44 As a side remark, the polymorphism of PBTTT- 8 O evidenced in the pristine films seems to have little influence on the TE performances of doped films.…”

Fluorinated Alcohol-Processed N-Type Organic Electrochemical Transistor with High Performance and Enhanced Stability

“…Compared with an almost 1:1 ratio of edge-on and face-on orientations for gNR-CF , the films cast from FAs show crystallites with a very high ratio of edge-on orientations, 94.8, 86.3, and 84.2% for gNR-6FOH , gNR-3FOH , and gNR-9FOH , respectively. Therefore, the predominance of edge-on orientation and tighter molecular packing for FA cast films are conducive to the effective charge transport in the parallel direction of the device architecture. , To gain insight into the crystallinity difference of gNR in thin films, coherence lengths (CLs) and paracrystalline disorder ( g ) were calculated from the width of the π–π stacking diffraction peaks (CL = 2π K /FWHM, K = 0.9, ). , As shown in Figure S16c, the gNR thin films formed with FAs displayed further enhanced crystalline packing: the CL values of the (010) peaks along the IP direction increased from 47.9 Å for CF to 59.5 Å for 3FOH, 71.5 Å for 6FOH, and 54.9 Å for 9FOH. Meanwhile, the CLs of the emerging (020) peak were also calculated to be 60.8 Å for 3FOH, 93.0 Å for 6FOH, and 59.4 Å for 9FOH; the largest CLs of the films in both (010) and (020) peaks endow gNR-6FOH the highest electron mobility. ,, In addition, the lower paracrystalline disorder of π–π stacking for FA cast films (Figure S16d) also suggests the further structural ordering, which leads to a reduction of the number of structural trapping sites for the electron carriers and indicates a strong correlation with charge transport properties. , It is worth noting that the combination of edge orientation predominance, closer molecular stacking, and enhanced crystallinity always leads to a more effective electronic transport; i.e., gNR-6FOH possesses the highest 1.78 × 10 –2 cm 2 V –1 s –1 compared to 1.25 × 10 –2 cm 2 V –1 s –1 for gNR-CF , owing to its highest edge-on orientation ratio, closest distance and maximum coherence length, and lowest paracrystalline disorder for (020) π–π stacking .…”

“…). 59,60 As shown in Figure S16c, the gNR thin films formed with FAs displayed further enhanced crystalline packing: the CL values of the (010) peaks along the IP direction increased from 47.9 Å for CF to 59.5 Å for 3FOH, 71.5 Å for 6FOH, and 54.9 Å for 9FOH. Meanwhile, the CLs of the emerging (020) peak were also calculated to be 60.8 Å for 3FOH, 93.0 Å for 6FOH, and 59.4 Å for 9FOH; the largest CLs of the films in both ( 010) and (020) peaks endow gNR-6FOH the highest electron mobility.…”

“…16,17 Up to now, only three sets of n-type OECT small molecular semiconductors have been reported. One is 2-(2,3,4-tris(methoxtriglycol) phenyl) [60]fulleropyrrolidine (C60-TEG), which exhibits a μC* of 7 F cm −1 V −1 s −1 . 18 The other is the glycolated perylene diimide (PDI) series with a μC* value of 0. good operational stability.…”

Conformational Heterogeneity and Interchain Percolation Revealed in an Amorphous Conjugated Polymer

“…The effects of internal dihedral rotation upon the emission spectrum and efficiency of conjugated polymer thin films have been studied experimentally, 11 while in highly doped conjugated polymers, paracrystalline disorder, rather than the ionic size of the doping ions, has been shown to control charge transport. 12 Predicting crystal structures of different conjugated polymers and how this structure impacts their properties is a current area of research; 13 however, a higher degree of crystallinity has been shown to not necessarily lead to an increase in charge-carrier mobility. 14 Recently, cryogenic tunnelling electron microscopy has been used to study the nanoscale structure of CPNs.…”