Microscopic mechanisms behind the high mobility in rubrene single-crystal transistors as revealed by field-induced electron spin resonance

Marumoto, Kazuhiro; Arai, Norimichi; Goto, Hiromasa; Kijima, Masashi; Murakami, Kouichi; Tominari, Yukihiro; Takeya, Jun; Shimoi, Yukihiro; Tanaka, Hisaaki; Kuroda, Shin–ichi; Kaji, Tatsuru; Nishikawa, Takao; Takenobu, Taishi; Iwasa, Yoshihiro

doi:10.1103/physrevb.83.075302

Cited by 66 publications

(64 citation statements)

References 27 publications

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“…This may indicate that the gate voltage dependence of the mobility is negligible in the rubrene device, although the carrier concentration ratio is even smaller than the expected value in the case of β = 2. This result is supported by the transfer characteristics showing a linear I ds 1/2 -V gs dependence, 36 as well as the narrow and V gs -independent FI-ESR line width in the rubrene devices. 38 These facts may indicate that the rubrene single-crystal transistor, fabricated by the lamination technique, produces few deep trap states, resulting in the high charge carrier mobilities.…”

Section: A Fi-esr Measurements On Metal-insulator-semiconductor Confsupporting

confidence: 72%

“…26 So far, this method has been applied to various OFETs of poly(3-alkylthiophene), [26][27][28][29][30] pentacene, [31][32][33] thienothiophene-based high-mobility materials, 34,35 and rubrene single crystals, 36 etc., giving microscopic information such as spin-charge relation, carrier wave function, motional effect of charge carriers, and local molecular orientation at the device interface. In particular, direct determination of spin concentration within the channel during device operation played a crucial role in clarifying the operation mechanism of OFETs, as was demonstrated for P3HT transistors using top-contact geometry, 37 and subsequently, for rubrene single-crystal transistors with bottom-contact geometry; 38 the spin concentration exhibited a clear decrease by applying V ds together with V gs in the linear region, whereas no V ds dependence was observed for the saturation region.…”

Section: Introductionmentioning

confidence: 99%

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Electron spin resonance observation of charge carrier concentration in organic field-effect transistors during device operation

et al. 2013

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Charge carrier concentration in operating organic field-effect transistors (OFETs) reflects the electric potential within the channel, acting as a key quantity to clarify the operation mechanism of the device. Here, we demonstrate a direct determination of charge carrier concentration in the operating devices of pentacene and poly(3-hexylthiophene) (P3HT) by field-induced electron spin resonance (FI-ESR) spectroscopy. This method sensitively detects polarons induced by applying gate voltage, giving a clear FI-ESR signal around g = 2.003 in both devices. Upon applying drain-source voltage, carrier concentration decreases monotonically in the FET linear region, reaching about 70% of the initial value at the pinch-off point, and stayed constant in the saturation region. The observed results are reproduced well from the theoretical potential profile based on the gradual channel model. In particular, the carrier concentration at the pinch-off point is calculated to be β/(β + 1) of the initial value, where β is the power exponent in the gate voltage (V gs ) dependence of the mobility (μ), expressed as μ ∝ V β−2 gs , providing detailed information of charge transport. The present devices show β = 2.6 for the pentacene and β = 2.3 for the P3HT cases, consistent with those determined by transfer characteristics. The gate voltage dependence of the mobility, originating from the charge trapping at the device interface, is confirmed microscopically by the motional narrowing of the FI-ESR spectra.

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Section: A Fi-esr Measurements On Metal-insulator-semiconductor Confsupporting

confidence: 72%

Section: Introductionmentioning

confidence: 99%

Electron spin resonance observation of charge carrier concentration in organic field-effect transistors during device operation

et al. 2013

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“…[39,40,41] It is not clear however if the obtained lengths should be associated to the presence of intrinsic thermal disorder or to trapping by extrinsic sources of disorder. In any case, these findings provide strong indications that a true quantum localization process takes place in organic semiconductors.…”

Section: Experimental Overviewmentioning

confidence: 99%

The Transient Localization Scenario for Charge Transport in Crystalline Organic Materials

Fratini

Mayou

Ciuchi

2016

Adv Funct Materials

338

452

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Charge transport in crystalline organic semiconductors is intrinsically limited by the presence of large thermal molecular motions, which are a direct consequence of the weak van der Waals inter-molecular interactions. These lead to an original regime of transport called transient localization, sharing features of both localized and itinerant electron systems. After a brief review of experimental observations that pose a challenge to the theory, we concentrate on a commonly studied model which describes the interaction of the charge carriers with inter-molecular vibrations. We present different theoretical approaches that have been applied to the problem in the past, and then turn to more modern approaches that are able to capture the key microscopic phenomenon at the origin of the puzzling experimental observations, i.e. the quantum localization of the electronic wavefuntion at timescales shorter than the typical molecular motions. We describe in particular a relaxation time approximation which clarifies how the transient localization due to dynamical molecular motions relates to the Anderson localization realized for static disorder, and allows us to devise strategies to improve the mobility of actual compounds. The relevance of the transient localization scenario to other classes of systems is briefly discussed.

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“…In the case of motional narrowing, ¦H pp with broad Lorentzian line width is approximately proportional to trapping time of charge carriers¸t r , which is considered to be governed by thermal activation. 12 The inset of Figure 4 shows the Arrhenius plot of ¦H pp , and data above 200 K follows the activation formula [exp(¦/kT)] with the activation energy ¦ of 0.011 eV (the solid line in the inset).…”

Section: ¹3mentioning

confidence: 99%

Electron Spin Resonance of Thin Films of N,N′-Di(1-naphthyl)-N,N′-diphenylbenzidine (NPB) Doped by Iodine Vapor

et al. 2012

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We have successfully observed the ESR signals of radical cations in the thin films of N,N¤-di(1-naphthyl)-N,N¤-diphenylbenzidine (NPB), typical hole-transport material, for the first time to our best knowledge. In order to characterize the radical cation state, ESR spectra obtained upon chemical doping with iodine are analyzed combined with density functional theory (DFT) calculation. The ESR line width is inversely correlated with doping concentration.Organic light-emitting diodes (OLEDs) have been actively studied because of their excellent characteristics such as high efficiency, low cost productivity, and flexibility.1,2 Aromatic amines are widely used as hole-transport materials in the devices. Among them, N,N¤-di(1-naphthyl)-N,N¤-diphenylbenzidine (NPB) (Scheme 1) is a typical one with high thermal stability.3 Blue-color luminescence was also reported in an OLED containing NPB layer.4 In order to understand the holetransport properties, it is quite important to elucidate the nature of cationic state. Since cations are usually accompanied by radical spins, electron spin resonance (ESR) spectroscopy is a useful technique for this purpose. Although the thin films of NPB have been characterized by various methods like photoemission, 5 time-of-flight, 6 infrared, 7 and Raman spectroscopies, 8 the ESR study of NPB film has not been reported to our best knowledge. We have utilized this technique for other organic materials in thin films 9 and in organic devices. 1012 In the present letter, we carried out chemical doping by exposing the NPB films to iodine vapor and successfully observed ESR signals arising from the induced radical cations. We also performed density functional theory (DFT) calculations to obtain insights to the radical cation state.By thermal vacuum evaporation under the pressure of 4 © 10 ¹4 Pa, NPB was deposited on a quartz substrate cleaned with isopropyl alcohol and acetone. The NPB film is 80nm in thickness and 0.84 cm 2 in area. Subsequently, the film was doped using iodine vapor under vacuum of 1 © 10 ¹1 Pa for 1 h, then it was sealed in an ESR sample tube. The doping concentration was reduced by exhausting the sample tube using a diffusion pump and was controlled by the length of the exhaustion time. ESR measurements for the sample were performed with a JEOL JES-FA200 ESR spectrometer.13 DFT calculations of the B3LYP/6-31G(d) level were carried out for an isolated NPB cation.14 The molecular geometry was fully optimized. The principal values of g tensor were computed using the gauge-independent atomic orbital method. Figure 1 shows observed ESR spectra: (a) spectrum observed right after the iodine doping and (b) that measured after an exhausting time of five hours. As seen in this figure, clear ESR signals were observed in both cases. In Figure 1a, g value, peak-to-peak ESR line width ¦H pp , and spin concentration of the ESR spectrum are 2.0040, 0.676 mT, and 2.65 © 10 20 cm ¹3, respectively. Meanwhile, in Figure 1b, they are 2.0036, 1.06 mT, and 2.12 © 10 19 cm ¹3, respectively. The spi...

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Microscopic mechanisms behind the high mobility in rubrene single-crystal transistors as revealed by field-induced electron spin resonance

Cited by 66 publications

References 27 publications

Electron spin resonance observation of charge carrier concentration in organic field-effect transistors during device operation

Electron spin resonance observation of charge carrier concentration in organic field-effect transistors during device operation

The Transient Localization Scenario for Charge Transport in Crystalline Organic Materials

Electron Spin Resonance of Thin Films of N,N′-Di(1-naphthyl)-N,N′-diphenylbenzidine (NPB) Doped by Iodine Vapor

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