Microscopic signature of insulator-to-metal transition in highly doped semicrystalline conducting polymers in ionic-liquid-gated transistors

Journal Article · Mon Dec 14 04:00:00 EST 2015 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.4938137· OSTI ID:22486249

Tanaka, Hisaaki; Nishio, Satoshi; Ito, Hiroshi; Kuroda, Shin-ichi ^[1]

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1. Department of Applied Physics, Nagoya University, Chikusa, Nagoya 464-8603 (Japan)

Electronic state of charge carriers, in particular, in highly doped regions, in thin-film transistors of a semicrystalline conducting polymer poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene), has been studied by using field-induced electron spin resonance (ESR) spectroscopy. By adopting an ionic-liquid gate insulator, a gate-controlled reversible electrochemical hole-doping of the polymer backbone is achieved, as confirmed from the change of the optical absorption spectra. The edge-on molecular orientation in the pristine film is maintained even after the electrochemical doping, which is clarified from the angular dependence of the g value. As the doping level increases, spin 1/2 polarons transform into spinless bipolarons, which is demonstrated from the spin-charge relation showing a spin concentration peak around 1%, contrasting to the monotonic increase in the charge concentration. At high doping levels, a drastic change in the linewidth anisotropy due to the generation of conduction electrons is observed, indicating the onset of metallic state, which is also supported by the temperature dependence of the spin susceptibility and the ESR linewidth. Our results suggest that semicrystalline conducting polymers become metallic with retaining their molecular orientational order, when appropriate doping methods are chosen.

• OSTI ID: 22486249
• Journal Information: Applied Physics Letters, Journal Name: Applied Physics Letters Journal Issue: 24 Vol. 107; ISSN APPLAB; ISSN 0003-6951
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABSORPTION SPECTRA
ANISOTROPY
CHARGE CARRIERS
DOPED MATERIALS
ELECTROCHEMISTRY
ELECTRON SPIN RESONANCE
G VALUE
HOLES
LIQUIDS
METALS
POLYCYCLIC SULFUR HETEROCYCLES
POLYMERS
SPECTROSCOPY
SPIN
TEMPERATURE DEPENDENCE
THIN FILMS
THIOPHENE
TRANSISTORS