Size- and Temperature-Dependent Charge Transport in PbSe Nanocrystal Thin Films

Kang, Moon Sung; Sahu, Ayaskanta; Norris, David J.; Frisbie, C. Daniel

doi:10.1021/nl2020153

Cited by 116 publications

(180 citation statements)

References 37 publications

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“…43,44 The transients are also thermally activated (Supporting Information Figures S5 and S6). Activated I D transients in PbX QD FETs have been observed by others and attributed to a barrier to trapping, 42 thermally activated ligand rearrangements, 43 or QD motion. Below ∼150 K, the transients were greatly suppressed for FETs without ALD and often completely eliminated for infilled FETs.…”

mentioning

confidence: 63%

“…The hole mobility increases by about a factor of 4 over the same range of sweep rate, which is caused by persistent I D transients for holes, even at low temperatures. 42,43 Together, these control experiments firmly establish that the change in dominant carrier type and mobility is a consequence of alumina infilling of the sulfide-capped QD films; that is, it is a property of the PbSe/Al 2 O 3 nanocomposite film itself, rather than a result of modifications to the gate dielectric, film heating, film annealing, or artifacts stemming from time-dependent drain currents.…”

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confidence: 73%

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PbSe Quantum Dot Field-Effect Transistors with Air-Stable Electron Mobilities above 7 cm² V^–1 s^–1

Liu¹,

Tolentino²,

Gibbs³

et al. 2013

Nano Lett.

226

322

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PbSe quantum dot (QD) field effect transistors (FETs) with air-stable electron mobilities above 7 cm 2 V −1 s −1 are made by infilling sulfide-capped QD films with amorphous alumina using lowtemperature atomic layer deposition (ALD). This high mobility is achieved by combining strong electronic coupling (from the ultrasmall sulfide ligands) with passivation of surface states by the ALD coating. A series of control experiments rule out alternative explanations. Partial infilling tunes the electrical characteristics of the FETs. KEYWORDS: Quantum dots, nanocrystals, lead selenide, field-effect transistors, solar cells T he recent introduction of metal chalcogenide complexes (MCCs) as ligands for colloidal quantum dots (QDs) 1 has triggered a flurry of research into inorganic ligands for fabricating high-performance all-inorganic QD solids for optoelectronic applications. 2−4 In addition to several demonstrations of MCC efficacy by Talapin and co-workers, 5−8 a variety of metal-free inorganic ions including chalcogenides, 9,10 halides, 11 thiocyanate, 12−14 and trialkyl oxonium 15 have been shown in initial studies to provide generally better performance in CdX and PbX (X = S, Se, Te) QD field-effect transistors (FETs) 6,7,12−14 and solar cells 11 than the small molecules, such as hydrazine 16 and 1,2-ethanedithiol (EDT), 17,18 traditionally used to replace the long-chain insulating organic ligands inherited from QD synthesis. Ionic inorganic ligands offer several key advantages over neutral molecular ligands. First, many inorganic ligands are ultrasmall and enable strong electronic coupling between QDs in films, which favors highmobility transport. Second, inorganic ions can quantitatively replace native long-chain ligands on the QD surface to produce charge-stabilized colloidal QD suspensions in polar media, in principle allowing the direct formation of conductive QD films from solution without the need for postassembly chemical or thermal treatments that can inhibit charge transport by increasing spatial and energetic disorder in the films. In practice, however, thermal treatments (150−300°C) are typically needed to achieve good transport in all-inorganic QD solids. Also, solution-phase exchange has so far failed to yield stable all-inorganic PbX QD colloids except with select hydrazine-free MCCs or mixed chalcogenide ions, 5,13 so postassembly ("solid state") ligand exchange has been employed instead to make PbX QD devices. 10−13,15 A third advantage of inorganic ligands is that they decompose, evaporate, or assimilate into the QDs at relatively low temperatures to create functional inorganic matrices (e.g., with MCCs) or direct QD−QD contact and partial QD necking/fusion (e.g., with S 2− and SCN − ). Despite the large site energy disorder induced by such annealing, 7,14,19 the electronic properties of films made with this approach may be adequate for many applications, including high-efficiency solar energy conversion. Recent reports of record mobilities for electrons in CdSe, 7,14 holes in PbX, 12,1...

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mentioning

confidence: 63%

mentioning

confidence: 73%

PbSe Quantum Dot Field-Effect Transistors with Air-Stable Electron Mobilities above 7 cm² V^–1 s^–1

Liu¹,

Tolentino²,

Gibbs³

et al. 2013

Nano Lett.

226

322

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“…Transport through a QDS is determined by the interplay between electronic coupling and the activation energy for interparticle hopping. 19 We consider three explanations for the greater hole mobilities observed for MeO À capping vs EDT capping: (1) a decrease of the activation energy due to an increase of the effective static dielectric constant of the ligand matrix, (2) an increase of electronic coupling, and (3) a smaller surface trap state density.…”

Section: Discussionmentioning

confidence: 99%

“…Assuming the same static dielectric constant of the ligand (ε L ), we calculate comparable values for the charging energy of EDT-and MeO À -capped particles, despite the differences in interparticle spacing (2À3 vs 5 Å). 19 In contrast, large differences in E C are observed when changing the static dielectric constant. For a 5.7 nm PbSe particle for instance, E C decreases from 9.3 meV to 2.1 meV upon changing ε L from 2.6 (as in Pb(EDT) 2 capping) to 10.…”

mentioning

confidence: 97%

Nonmonotonic Size Dependence in the Hole Mobility of Methoxide-Stabilized PbSe Quantum Dot Solids

et al. 2013

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We present a facile procedure to fabricate p-type PbSe-based quantum dot solids with mobilities as large as 0.3 cm2 V–1 s–1. Upon partial ligand exchange of oleate-capped PbSe quantum dots with the methoxide ion, we observe a pronounced red shift in the excitonic transition in conjunction with a large increase in conductivity. We show that there is little correlation between these two phenomena and that the electronic coupling energy in PbSe quantum dot solids is much smaller than often assumed. However, we observe for the first time a nonmonotonic size dependence of the hole mobility, illustrating that coupling can nonetheless be dominant in determining the transport characteristics. We attribute these effects to a decrease in charging energy and interparticle spacing, leading to enhanced electronic coupling on one hand and enhanced dipole interactions on the other hand, which is held responsible for the majority of the red shift.

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“…is usually seen to be positive with values around 0.25 (Mott variable-range hopping), 0.5 (Efros Shklovskii variable-range hopping) or 1.0 (Arrhenius-like nearest neighbor hopping) [15]. For this reason, a negative is often taken as an unambiguous sign for the occurrence of band-like transport.…”

Section: Temperature-dependent Carrier Mobilitymentioning

confidence: 99%

To Be or not to Be: Band-Like Transport in Quantum Dot Solids

Scheele¹

2014

Zeitschrift Für Physikalische Chemie

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Recent experimental data on charge carrier transport in quantum dot solids is analyzed in light of the question whether band-like transport is the most plausible mechanism to account for the observed behavior. Upon reviewing some physical fundamentals of temperature-activated hopping, small polaron hopping and band-like transport, it is established that a combined approach of different experimental methods is required to achieve a satisfactory degree of unambiguousness to address this question. In doing so, at least one example is identified for which a high degree of supporting evidence exists that transport is in fact diffusive. It is highlighted that temperature-dependent Hall Effect measurements play an important role in this respect.

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Size- and Temperature-Dependent Charge Transport in PbSe Nanocrystal Thin Films

Cited by 116 publications

References 37 publications

PbSe Quantum Dot Field-Effect Transistors with Air-Stable Electron Mobilities above 7 cm² V^–1 s^–1

PbSe Quantum Dot Field-Effect Transistors with Air-Stable Electron Mobilities above 7 cm² V^–1 s^–1

Nonmonotonic Size Dependence in the Hole Mobility of Methoxide-Stabilized PbSe Quantum Dot Solids

To Be or not to Be: Band-Like Transport in Quantum Dot Solids

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Size- and Temperature-Dependent Charge Transport in PbSe Nanocrystal Thin Films

Cited by 116 publications

References 37 publications

PbSe Quantum Dot Field-Effect Transistors with Air-Stable Electron Mobilities above 7 cm2 V–1 s–1

PbSe Quantum Dot Field-Effect Transistors with Air-Stable Electron Mobilities above 7 cm2 V–1 s–1

Nonmonotonic Size Dependence in the Hole Mobility of Methoxide-Stabilized PbSe Quantum Dot Solids

To Be or not to Be: Band-Like Transport in Quantum Dot Solids

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Product

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PbSe Quantum Dot Field-Effect Transistors with Air-Stable Electron Mobilities above 7 cm² V^–1 s^–1

PbSe Quantum Dot Field-Effect Transistors with Air-Stable Electron Mobilities above 7 cm² V^–1 s^–1