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

Journal Article · Mon Sep 17 00:00:00 EDT 2018 · Advanced Functional Materials

DOI:https://doi.org/10.1002/adfm.201803687· OSTI ID:1472162

Thomas, Elayne M. ^[1]; Brady, Michael A. ^[2]; Nakayama, Hidenori ^[3]; Popere, Bhooshan C. ^[4]; Segalman, Rachel A. ^[5]; Chabinyc, Michael L. ^[1]

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1. Materials Department University of California, Santa Barbara Santa Barbara CA 93106 USA
2. The Advanced Light Source Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
3. Materials Department University of California, Santa Barbara Santa Barbara CA 93106 USA, Electronics Materials and New Energy Laboratory Mitsubishi Chemical Corporation Yokohama R&,D Center 1000 Kamoshida‐cho Aoba‐ku Yokohama 227–8502 Japan
4. Department of Chemical Engineering University of California, Santa Barbara Santa Barbara CA 93106 USA
5. Materials Department University of California, Santa Barbara Santa Barbara CA 93106 USA, Department of Chemical Engineering University of California, Santa Barbara Santa Barbara CA 93106 USA

Abstract

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.

• Sponsoring Organization: USDOE
• Grant/Contract Number: SC0016390; AC02-05CH11231
• OSTI ID: 1472162
• Journal Information: Advanced Functional Materials, Journal Name: Advanced Functional Materials Journal Issue: 44 Vol. 28; ISSN 1616-301X
• Publisher: Wiley Blackwell (John Wiley & Sons)
• Country of Publication: Germany
• Language: English