ESR and Transport Studies in Electrochemically Doped Polythiophene Film

Kaneto, Keiichi; Hayashi, Shigenori; Ura, Shogo; Yoshino, Katsumi

doi:10.1143/jpsj.54.1146

Cited by 162 publications

(51 citation statements)

References 9 publications

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“…This relaxation results in the appearance of new optical transitions in the absorption spectrum at energies beneath the maintransition upon charge injection. These transitions have been detected experimentally [6][7][8][9][10][11][12][13][14] and are in good agreement 15 with the quantum chemical calculations of Cornil et al [16][17][18][19] performed on isolated oligomers ͑see Fig. 2͒ and earlier tightbinding models of isolated, one-dimensional polymer chains developed by Su, Schrieffer, and Heeger ͑the SSH model͒ ͑Ref.…”

Section: Introductionsupporting

confidence: 84%

“…To our knowledge, such a pronounced vibrational structure in the bleaching signal has not been previously reported for a conjugated polymer using CMS or chemical doping of thin solid films. 10,11 The following experimental observations suggest that the charged species in high-mobility P3HT FET's is a singlycharged polaronic carrier, as opposed to a doubly charged bipolaronic species:…”

Section: Discussionmentioning

confidence: 99%

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Optical spectroscopy of field-induced charge in self-organized high mobility poly(3-hexylthiophene)

et al. 2001

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Charge modulation spectroscopy ͑CMS͒ is an electro-optical spectroscopic technique that allows the charge carriers present in the conducting channels of field-effect transistors ͑FET's͒ to be studied in situ. We use this technique to study the charge carriers present in regio-regular poly͑3-hexylthiophene͒ P3HT that has been shown to exhibit high field-effect mobilities of up to 0.1 cm 2 /Vs, similar to that observed for amorphous silicon. We demonstrate that the CMS spectra of charge carriers in high-mobility regio-regular P3HT FET's are independent of charge density, modulation frequency, and temperature. This is evidence for the presence of a single, intrinsic charge carrier that we identify as a singly charged polaronic species. The spectral features attributed to the charged species show a lack of vibronic structure that is in contrast to the vibronic structure present in the bleaching of the main -* absorption of the neutral chains. The transition energies observed in regio-regular P3HT cannot be understood as an extrapolation of charge-induced transitions in isolated short-chain oligomers to long conjugation lengths. Our results give evidence that interchain coupling in highly ordered P3HT is sufficiently strong so that the charge carriers cannot be considered to be confined to a single chain, rather, they now exhibit quasi-two-dimensional characteristics.

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Section: Introductionsupporting

confidence: 84%

Section: Discussionmentioning

confidence: 99%

Optical spectroscopy of field-induced charge in self-organized high mobility poly(3-hexylthiophene)

et al. 2001

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“…0.02 spins per meric unit, corresponding to 1 spin per 50 monomer units on average. This is a relatively high value compared with other undoped conjugated polymers like polythiophene (PT) or polypyrrole where the residual number of spins associated with polymer defects can be as low as 1 × 10 −4 [32] or 5 × 10 −3 [33] spins per mer accordingly. With increasing potential, concentration of spins changes little at first, however onward from −0.9 V a gradual increase is observed.…”

Section: Resultsmentioning

confidence: 98%

Quantitative in-situ EPR spectroelectrochemical studies of doping processes in poly(3,4-alkylenedioxythiophene)s

Domagała

Pilawa

Łapkowski

2008

Electrochimica Acta

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“…The polaron band red-shifts considerably with the doping level of the polymer, [23] and with the intermolecular interaction of the oligomers, [24] but its peak absorption cross-section s p Figure 2. FTIR spectra of a rr-P3HT film acquired sequentially after different in-situ exposure to cleanroom air.…”

mentioning

confidence: 99%

Direct Spectroscopic Evidence for a Photodoping Mechanism in Polythiophene and Poly(bithiophene‐alt‐thienothiophene) Organic Semiconductor Thin Films Involving Oxygen and Sorbed Moisture

et al. 2009

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Fourier-transform infrared spectroscopy of two prototypical high-mobility polymer organic semiconductors (OSCs), regioregular poly(3-hexylthiophene) (rr-P3HT) and poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno(3,2-b)thiophene] (PBTTT), reveals photoinduced doping that involves both oxygen and water dissolved in the polymer matrix when exposed to light. The equilibrium concentration of water at room temperature and 60% relative humidity in these films is $2 Â 10 19 cm À3, and exists primarily as monomers, with a small population of dimers and trimers. Photo-excitation in room light ultimately generates a polaron density of the order of a few 10 17 cm À3, which is sufficient to degrade the saturation and 'on-off' characteristics of organic field-effect transistors, and the dark current of organic photovoltaics. The dopant anion has been identified primarily to be hydroxide ion species. This process occurs to a smaller extent in wet nitrogen, but even less in dry oxygen, which points to a key role of the dissolved water. The relative stability of PBTTT over rr-P3HT is found to be largely kinetic in origin, attributed to its higher crystallinity (X-ray diffraction crystallinity 27% vs 21% in rr-P3HT), and shorter pÁÁÁp stacking distance (3.64 Å vs 3.78 Å in rr-P3HT), which gives better moisture exclusion from its thiophene backbone.Understanding the degradation mechanisms of polymer organic semiconductor (OSC) devices is an essential step to develop more robust OSC systems and their devices, whether in light-emitting diodes (LEDs), field-effect transistors (FETs), or photovoltaics (PVs). Despite decades of research, detailed spectroscopic studies have seldom been reported, [1,2] primarily because of the considerable challenges to identify chemical transformations that occur on sub-1-mol % of repeat units in the thin films. Yet changes at these levels can be electronically significant. The typical carrier density for LED operation [3] is $1 Â 10 18 cm À3 , which is approximately 0.05 mol % of repeat units, assuming a unit molecular weight of 300 g mol À1 and density of 1.1 g cm À3. For organic FETs, doping at this level can open a parallel source-drain conduction path in the bulk that degrades the shut 'off' and saturation characteristics. [4,5] A simple performance figure-of-merit is the 'on-off' ratio, which for long-channel FETs with a small drain voltage V d and an off-state defined at a gate voltage (V g ) of 0 V is given by i on / i off ¼ mC ox (V g À V th )/(sd), where m is the carrier mobility, C ox is the gate-dielectric capacitance, (V g À V th ) is the effective gate voltage, s is the shunt conductance, and d is the film thickness. For m $ 0.1 cm 2 V À1 s À1 , d $ 30 nm, and typical values for the other parameters, we require s < 10 À8 S cm À1 to give an i on /i off ratio > 10 6

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ESR and Transport Studies in Electrochemically Doped Polythiophene Film

Cited by 162 publications

References 9 publications

Optical spectroscopy of field-induced charge in self-organized high mobility poly(3-hexylthiophene)

Optical spectroscopy of field-induced charge in self-organized high mobility poly(3-hexylthiophene)

Quantitative in-situ EPR spectroelectrochemical studies of doping processes in poly(3,4-alkylenedioxythiophene)s

Direct Spectroscopic Evidence for a Photodoping Mechanism in Polythiophene and Poly(bithiophene‐alt‐thienothiophene) Organic Semiconductor Thin Films Involving Oxygen and Sorbed Moisture

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