Charge Density and Film Morphology Dependence of Charge Mobility in Polymer Field‐Effect Transistors

Shaked, Sagi; Tal, Shay; Roichman, Yohai; Razin, Alexey; Xiao, Steven; Eichen, Yoav; Tessler, Nir

doi:10.1002/adma.200304653

Cited by 71 publications

(70 citation statements)

References 27 publications

(29 reference statements)

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“…The carrier mobility also depends on the drift field, the carrier density and temperature. [13][14][15][16][17][18][19][20] In field-effect transistors (FETs) operating in the linear regime, the dependence of the mobility on the drift field can be neglected since the geometry of the device generates small lateral fields (~ few 10 4 V/cm) for typical device geometries (channel length>5 µm). We use the dependence of the mobility on carrier density and temperature to determine the transport mechanism and other properties of the polymer, such as its free carrier mobility and the shape of the DOS.…”

Section: -Introductionmentioning

confidence: 99%

Intrinsic hole mobility and trapping in a regioregular poly(thiophene)

et al. 2004

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The transport properties of high-performance thin-film transistors (TFT) made with a regio-regular poly(thiophene) semiconductor (PQT-12) are reported. The roomtemperature field-effect mobility of the devices varied between 0.004 cm 2 /V s and 0.1 cm 2 /V s and was controlled through thermal processing of the material, which modified the structural order. The transport properties of TFTs were studied as a function of temperature. The field-effect mobility is thermally activated in all films at T<200 K and the activation energy depends on the charge density in the channel. The experimental data is compared to theoretical models for transport, and we argue that a model based on the existence of a mobility edge and an exponential distribution of traps provides the best interpretation of the data. The differences in room-temperature mobility are attributed to different widths of the shallow localized state distribution at the edge of the valence band due to structural disorder in the film. The free carrier mobility of the mobile states in the ordered regions of the film is the same in all structural modifications and is estimated to be between 1 and 4 cm 2 /V s.2 1-IntroductionThe carrier mobility of polymer semiconductors has improved tremendously over the past few years. Field-effect mobility as high as 0.1 cm 2 /V s has recently been measured in regio-regular poly(thiophenes). [1][2][3] Transport characteristics are strongly dependent on the degree of order of the polymer semiconductor at the dielectric interface. Because the structure of the polymer depends on the processing conditions, it is not uncommon to find in the literature widely differing mobility values obtained for nominally the same polymer. In particular, the energy of the dielectric surface prior to the deposition of the polymer, 4-7 the solvent evaporation rate, 2 the molecular weight of the polymer 8 and thermal post-processing of the film 9 all influence the carrier mobility.There is no general consensus on the mechanism of charge transport in these amorphous or poly-crystalline materials. A complete model of the electrical properties should include a description of the energy distribution of the carriers and how the conduction varies as a function of energy. Disorder-induced localized states are clearly important for the transport, and the essential question is the relation between atomic structure, electronic structure and the transport. Generally, charge transport in disordered materials is described either as hopping between localized states, or trapping and release from localized states into a higher energy mobile state. 10 The degree of structural order may change the mechanism even within the same class of polymer.Because the electronic structure of semiconducting polymer films is not known experimentally, a simplified model has to be assumed. The model proposed by Bässler 11 assumes that the energy distribution of the carriers is Gaussian due to the random disorder in the material. The standard deviation of the Gaussian (typicall...

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Section: -Introductionmentioning

confidence: 99%

Intrinsic hole mobility and trapping in a regioregular poly(thiophene)

et al. 2004

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“…The gate-voltage-dependent mobilities found in this study are not uncommon in the field of solution-processed OFETs. [15][16][17][18] This phenomenon was found to originate from charge-density-dependent mobilites 16 and has often been attributed to the existence of disorder 15 or the presence of traps. 17,18 For both materials, the ambipolar mobilities were most optimized on as-spun polymer films.…”

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confidence: 99%

Thieno[3,2-b]thiophene−Diketopyrrolopyrrole-Containing Polymers for High-Performance Organic Field-Effect Transistors and Organic Photovoltaic Devices

et al. 2011

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ABSTRACT:We report the synthesis and polymerization of a novel thieno[3,2-b]thiophene-diketopyrrolopyrrolebased monomer. Copolymerization with thiophene afforded a polymer with a maximum hole mobility of 1.95 cm 2 V -1 s -1 , which is the highest mobility from a polymer-based OFET reported to date. Bulk-heterojunction solar cells comprising this polymer and PC 71 BM gave a power conversion efficiency of 5.4%. T here is considerable interest in the synthesis of narrow-bandgap conjugated polymers for use in organic photovoltaic (OPV) and organic field-effect transistor (OFET) devices. Their solution processability and mechanical properties allow access to a new generation of cheap and flexible transistors and solar devices. Current state of the art polymeric materials have allowed for the fabrication of OFETs with mobilities of ∼1 cm 2 V -1 s -1 1 and OPV devices with power conversion efficiencies (PCEs) of over 7%.2 Diketopyrrolopyrrole (DPP)-based copolymers have emerged as extremely attractive materials for both thin-film transistors and solar cell devices in recent years. The DPP core's electrondeficient nature has been exploited for the synthesis of extremely narrow band gap donor-acceptor-type materials that are wellsuited for use in OPVs with high PCEs reported from both small molecules and polymers.3-6 Furthermore, the planarity of the DPP skeleton and its ability to accept hydrogen bonds (and other types of electrostatic interactions) result in copolymers that encourage π-π stacking. Typically, these DPP-based copolymers are prepared via either Suzuki or Stille coupling of the 3,6-bis(5-bromothiophen-2-yl)-2,5-dialkylpyrrolo[3,4-c]pyrrole-1,4-(2H,5H)-dione core with the desired comonomer, which as a result means that the electron-deficient DPP unit is always flanked by two thiophenes. Variation of the comonomer has yielded polymers with extremely attractive properties for both OPV and OFET devices. For instance, copolymerization with thiophene derivatives or benzothiadiazole resulted in polymers with impressive ambipolar charge-carrier mobilities. 7,8 Recently, a copolymer of 3,6-bis(5-bromothiophen-2-yl)-N,N 0 -bis(2-octyl-1-dodecyl)-1,4-dioxopyrrolo[3,4-c]pyrrole and 2,5-bis(trimethylstannyl)thieno[3,2-b]thiophene showed an impressive hole mobility of ∼0.9 cm 2 V -1 s -1 . 9 In terms of materials for OPVs, copolymerization of the same DPP monomer (albeit having a slightly different solubilizing alkyl chain) with phenylene-1,4-diboronic acid bispinacol ester afforded a polymer that was used to fabricate OPV devices with efficiencies of ∼5.5%. 10Despite the significant number of reports on DPP-based copolymers, there have been very few studies on the effect of modifying the 3,6-bis(5-bromothiophen-2-yl)-2,5-dialkylpyrrolo-[3,4-c]pyrrole-1,4-(2H,5H)-dione monomer. One very recent example was the replacement of the flanking thiophenes by furans, which resulted in polymers with high PCEs in solar cell devices. 11 We were interested in increasing the intermolecular association of DPP-based copolymers by repla...

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“…Increasing the degree of disorder in inorganic semiconductors reduces carrier mobility because carriers spend more of their time in localized states and transport occurs via hopping or tunneling between states leading to low effective mobilities. Similarly in polymers charge transport is by hopping in a disordered system [13] with a mobility that seems to be related in a complicated and unresolved manner to charge density and film morphology [14]. A low carrier mobility is therefore a basic property of hopping transport, and there is not very much we can do about it.…”

Section: Disordered and Poor-quality Semiconductorsmentioning

confidence: 99%

High-Performance Thin-Film Transistors in Disordered and Poor-Quality Semiconductors

Shannon

Balon

2007

IEEE Trans. Electron Devices

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Abstract-In general, the range of applications for large-area electronics or macroelectronics is limited by the quality of the semiconductor used to make the electronic devices and circuits. Here, we address the question of how to make high-performance transistors using semiconductors that are defective, have low carrier mobilities, and are unstable. It is proposed that we need to engineer and operate a transistor that minimizes the excess carrier concentration throughout the device combined with high internal fields over small dimensions. Compared with the fieldeffect transistor, a source-gated transistor more nearly meets these requirements. Using the unstable and defective semiconductor, hydrogenated amorphous silicon, it is shown that high-performance thin-film transistors can indeed be made using the source-gated concept.

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Charge Density and Film Morphology Dependence of Charge Mobility in Polymer Field‐Effect Transistors

Cited by 71 publications

References 27 publications

Intrinsic hole mobility and trapping in a regioregular poly(thiophene)

Intrinsic hole mobility and trapping in a regioregular poly(thiophene)

Thieno[3,2-b]thiophene−Diketopyrrolopyrrole-Containing Polymers for High-Performance Organic Field-Effect Transistors and Organic Photovoltaic Devices

High-Performance Thin-Film Transistors in Disordered and Poor-Quality Semiconductors

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