Sequential Doping Reveals the Importance of Amorphous Chain Rigidity in Charge Transport of Semi-Crystalline Polymers

Chew, Annabel R.; Ghosh, Raja; Shang, Zhengrong; Spano, Frank C.; Salleo, Alberto

doi:10.1021/acs.jpclett.7b01989

Cited by 83 publications

(159 citation statements)

References 35 publications

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“…18 Similar ndings were made by Scholes et al 19 and Chew et al 20 who concluded that the ordered regions of P3HT give rise to a higher chargecarrier mobility and therefore lead to an increase in the electrical conductivity. Here, we explore how the crystallinity inuences the power factor of P3HT vapour-doped with F4TCNQ.…”

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confidence: 52%

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Influence of crystallinity on the thermoelectric power factor of P3HT vapour-doped with F4TCNQ

2018

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Doping of the conjugated polymer poly(3-hexylthiophene) (P3HT) with the p-dopant 2, 3,5,7,8, is a widely used model system for organic thermoelectrics.We here study how the crystalline order influences the Seebeck coefficient of P3HT films doped with F4TCNQ from the vapour phase, which leads to a similar number of F4TCNQ anions and hence (bound + mobile) charge carriers of about 2 Â 10 À4 mol cm À3. We find that the Seebeck coefficient first slightly increases with the degree of order, but then again decreases for the most crystalline P3HT films. We assign this behaviour to the introduction of new states in the bandgap due to planarisation of polymer chains, and an increase in the number of mobile charge carriers, respectively. Overall, the Seebeck coefficient varies between about 40 to 60 mV K À1. In contrast, the electrical conductivity steadily increases with the degree of order, reaching a value of more than 10 S cm À1, which we explain with the pronounced influence of the semi-crystalline nanostructure on the charge-carrier mobility. Overall, the thermoelectric power factor of F4TCNQ vapour-doped P3HT increases by one order of magnitude, and adopts a value of about 3 mW m À1 K À2 in the case of the highest degree of crystalline order.

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confidence: 52%

“…[18][19][20] By tuning the regioregularity and processing solvent the nanostructure of P3HT could be altered leading to a much higher electrical conductivity. For example, by changing the polymer processing solvent we were able to increase the electrical conductivity from 0.01 to 13 S cm…”

Section: 18mentioning

confidence: 99%

Influence of crystallinity on the thermoelectric power factor of P3HT vapour-doped with F4TCNQ

2018

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“…While the distribution of counterions in the active layer is straightforward to interpret from Figures and , the precise location of a charge carrier within semicrystalline polymer films remains to be a topic of debate . The lower ionization energy in a crystallite of P3HT has been shown to lead to increased doping efficiency and more delocalized polarons .…”

Section: Resultsmentioning

confidence: 99%

“…The lower ionization energy in a crystallite of P3HT has been shown to lead to increased doping efficiency and more delocalized polarons . Some suggest that a carrier should be in close proximity to its associated counterion, regardless of the carrier concentration . Previously, charge modulation spectroscopy, FTIR, and Raman spectroscopy have been used to study the local environment of polarons in conjugated polymers at low concentrations, typically to determine if holes exist as polarons or bipolarons .…”

Section: Resultsmentioning

confidence: 99%

X‐Ray Scattering Reveals Ion‐Induced Microstructural Changes During Electrochemical Gating of Poly(3‐Hexylthiophene)

Thomas

Brady

Nakayama

et al. 2018

Adv Funct Materials

153

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The heterogeneous microstructure of semicrystalline polymers complicates the relationship between their electrical conductivity and carrier concentration. Charge transport models typically describe conductivity with an assumption of uniform doping throughout the material. Here, the evolution in morphology and optoelectronic properties of poly(3-hexylthiophene) (P3HT) is reported as a function of carrier concentration in an organic electrochemical transistor using a polymeric ionic liquid (PIL) as the gate insulator. Operando grazing incidence X-ray scattering reveals that negatively charged ions from the dielectric first infiltrate the amorphous regions of the semiconductor, and then penetrate the crystalline regions at a critical carrier density of 4 × 10 20 cm −3 . Upon infiltration, the crystallites expand by 12% in the alkyl stacking direction and compress by 4% in the π-π stacking direction. The change in crystal structure of P3HT correlates with a sharply increasing effective carrier mobility. UV-visible spectroscopy reveals that holes induced in P3HT first reside in the crystalline regions of the polymer, which verifies that a charge carrier need not be in the same physical domain as its associated counterion. The dopant-induced morphological changes of P3HT rationalize the dependence of mobility on carrier concentration, suggesting a phase transition of crystalline regions at high carrier concentration.

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“…To provide further insight into the PIA spectrum, a modified Holstein Hamiltonian is used to simulate the polaron absorption as previously described, achieving a qualitative fit to the PIA spectrum ( Figure ). Details of the spectral line shape can be found elsewhere . From the simulated spectrum, the number of coherently connected thiophene units in the intrachain direction ( N intra ) can be calculated to be ≈3, consistent with the polaron being localized on single‐coiled chains.…”

Section: Resultsmentioning

confidence: 99%

Unraveling the Effect of Conformational and Electronic Disorder in the Charge Transport Processes of Semiconducting Polymers

Chew

Ghosh

Pakhnyuk

et al. 2018

Adv Funct Materials

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Charge transport in semiconducting polymers is inextricably linked to their microstructure, making the characterization of polymer morphology at all length-scales essential for understanding the factors that limit mobility in these materials. Indeed, charge transport depends both on the ability of polarons to delocalize at the approximately nanometer length-scale and navigate a complex energetic and morphological mesoscale landscape. While characterization of the mesoscale morphology of polymers is wellestablished, studies of the local chain packing and nanoscale disorder, which affect delocalization, can be significantly more difficult to carry out. Through infrared charge modulation spectroscopy and theoretical modeling, the effect of the local chain environment on polaron delocalization is directly measured and quantified. Using a series of polymers based on the model system, poly(3-hexylthiophene), the link between disorder and polaron localization is systematically explored. Polaron delocalization is correlated with known trends in mobility, revealing that while charge delocalization is always beneficial, the formation of tie-chains is necessary to reach the highest mobilities in semicrystalline polymers. The results provide direct evidence for the importance of both nanoscale (charge carrier delocalization) and mesoscale (tie-chains) orders, demonstrating the need to distinguish the key length-scale limiting charge transport in the design of new, high mobility polymers.

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Sequential Doping Reveals the Importance of Amorphous Chain Rigidity in Charge Transport of Semi-Crystalline Polymers

Cited by 83 publications

References 35 publications

Influence of crystallinity on the thermoelectric power factor of P3HT vapour-doped with F4TCNQ

Influence of crystallinity on the thermoelectric power factor of P3HT vapour-doped with F4TCNQ

X‐Ray Scattering Reveals Ion‐Induced Microstructural Changes During Electrochemical Gating of Poly(3‐Hexylthiophene)

Unraveling the Effect of Conformational and Electronic Disorder in the Charge Transport Processes of Semiconducting Polymers

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