PbS Nanoparticles Capped with Tetrathiafulvalenetetracarboxylate: Utilizing Energy Level Alignment for Efficient Carrier Transport

Scheele, Marcus; Hanifi, David; Zherebetskyy, Danylo; Chourou, Slim; Axnanda, Stephanus; Rancatore, Benjamin J.; Thorkelsson, Kari; Xu, Ting; Liu, Zhi; Wang, Lin‐Wang; Liu, Yi; Alivisatos, A. Paul

doi:10.1021/nn406127s

Cited by 45 publications

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“…34 Since the optoelectronic properties of PbS NC ensembles bear many opportunities for applications in solar cells or photodetectors, a number of ligand exchange procedures with small organic or inorganic molecules as well as single atom passivation strategies have been developed, all of which greatly increase the carrier mobilities within the SL of NCs. 28,33,[35][36][37][38][39][40][41][42][43][44] Due to the short interparticle spacing imposed by these ligands, structural coherence is mostly lost in such superlattices, but in rare cases it has been demonstrated that significant long-range order and even mesocrystallinity can be preserved. 25,35,45 However, a persisting problem of these protocols is that they are prone to introduce defects in the superlattice structure with some degree of granularity and significantly smaller grain sizes, which poses difficulties in determining the angular correlation with a meaningful statistical distribution.…”

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confidence: 99%

Quantifying Angular Correlations between the Atomic Lattice and the Superlattice of Nanocrystals Assembled with Directional Linking

et al. 2017

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We show that the combination of X-ray scattering with a nanofocused beam and X-ray cross correlation analysis is an efficient means for the full structural characterization of mesocrystalline nanoparticle assemblies with a single experiment. We analyze several hundred diffraction patterns of individual sample locations, i.e. individual grains, to obtain a meaningful statistical distribution of the superlattice and atomic lattice ordering. Simultaneous small-and wide-angle X-ray scattering of the same sample location allows us to determine the structure and orientation of the superlattice as well as the angular correlation of the first two Bragg peaks of the atomic lattices, their orientation with respect to the superlattice, and the average orientational misfit due to local structural disorder. This experiment is particularly advantageous for synthetic mesocrystals made by the simultaneous self-assembly of colloidal nanocrystals and surfacefunctionalization with conductive ligands. While the structural characterization of such materials has been challenging so far, the present method now allows correlating mesocrystalline structure with optoelectronic properties. Mesocrystals (MC) are three-dimensional arrays of iso-oriented single-crystalline particles with an individual size between 1 -1000 nm. [1][2][3][4][5] Their physical properties are largely determined by structural coherence, for which the angular correlation between their individual atomic lattices and the underlying superlattice of nanocrystals (NC) is a key ingredient. 1,2 Colloidal NCs stabilized by organic surfactants have been shown to pose excellent building blocks for the design of synthetic MCs with tailored structural properties which are conveniently obtained by self-assembly of NCs from solution on a solid or liquid substrate by exploiting ligand-ligand 3 interactions. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Typically, the utilized ligands consist of wide-gap, bulky hydrocarbons which render the MCs insulating. [26][27][28][29][30][31][32][33] MCs obtained in this way exhibit average grain sizes of ~150 µm 2 , which enables a detailed characterization by electron and/or X-ray microscopy. 34 Since the optoelectronic properties of PbS NC ensembles bear many opportunities for applications in solar cells or photodetectors, a number of ligand exchange procedures with small organic or inorganic molecules as well as single atom passivation strategies have been developed, all of which greatly increase the carrier mobilities within the SL of NCs. 28,33,[35][36][37][38][39][40][41][42][43][44] Due to the short interparticle spacing imposed by these ligands, structural coherence is mostly lost in such superlattices, but in rare cases it has been demonstrated that significant long-range order and even mesocrystallinity can be preserved. 25,35,45 However, a persisting problem of these protocols is that they are prone to introduce defects in the superlattice structure with some degree of granularity and signifi...

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Quantifying Angular Correlations between the Atomic Lattice and the Superlattice of Nanocrystals Assembled with Directional Linking

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“…Similar works on mixtures of DTCP with P3HT or Au nanoparticles indicate that this conversion can indeed be achieved [5,26]. Since significantly coupled PbS QDs exhibit much higher carrier mobilities than P3HT, establishing a similar photoswitchability in this material is expected to give rise to optically addressable transistors or even memory elements with high efficiencies [27,28].…”

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confidence: 73%

Towards Photo-Switchable Transport in Quantum Dot Solids

Schedel

Thalwitzer

Khoshkhoo

et al. 2016

Zeitschrift Für Physikalische Chemie

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Abstract:We use the photochromic organic semiconductor 1,2-Bis(5′-carboxy-2′-methylthien-3′-yl)-cyclopentene (DTCP) to cross-link PbS quantum dots assembled into thin films. The ligand exchange is monitored by means of vibrational spectroscopy (FT-IR) and core-level X-ray photoemission spectroscopy (XPS). Transport measurements in a field-effect transistor (FET) set-up reveal ambipolar behavior with hole and electron mobilities on the order of 10 −4 cm 2 /Vs and 10 −5 cm 2 /Vs, respectively. Exposure to UV light from a 4 W UV lamp does not significantly change the transport properties, indicating that switching of DTCP is hindered in the hybrid film. We find a pronounced photo-conductance with rapid and reversible photo-response on the order of few seconds, which we attribute to (de-)filling of QD trap states. Our results indicate that hybrid, nanostructured networks of PbS QDs cross-linked with DTCP can be obtained by the presented procedure but that switching of the QD-bound DTCP appears to be hindered compared to the pure, unbound molecular species. We discuss future means to address this problem.

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“…Moreover, organic molecules (both ligands and additives) in CQD films can affect the electronic coupling between the adjacent dots. Tuning the (mis)alignment of the HOMO or LUMO of the molecule with the matching states in the CQDs allows for suppressing or enhancing the coupling for one of the carriers, and determining changes in the apparent device polarity . Addition of ligands can also modify the density of states of the single CQDs, as observed from the increased absorbance of CQDs capped with arene‐thiolates, and the effect can be fine‐tuned with functional side groups attached to the aromatic ring …”

Section: Surface‐based Control Of the Electronic Propertiesmentioning

confidence: 99%

Lead‐Chalcogenide Colloidal‐Quantum‐Dot Solids: Novel Assembly Methods, Electronic Structure Control, and Application Prospects

Balazs

Loi

2018

Advanced Materials

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Colloidal particles are formed and stabilized by surrounding the core with a surfactant shell that keeps the CQDs isolated and prevents charge transport though the arrays. [6] Replacing this shell by shorter molecules, so-called ligands, decreases the interparticle distance and increases the electronic coupling. This is thus a crucial step in forming conductive, practically relevant assemblies.Most early studies relied on a repetitive, layer-by-layer deposition and ligand exchange of CQDs to achieve thick conductive films, a method that resulted in the demonstration of field effect transistors and solar cells of noteworthy performances. [7][8][9][10][11][12][13][14][15] However, this technique only allows for limited control of the nanostructure and is not suitable for upscaling. The last few years brought several improvements in controlling the properties of CQD thin films with focus on both applications and the underlying science. [16,17] Current solar cells and transistors based on CQD arrays are on par with or better than the semiconducting polymer-based devices, showing the true prospects of these materials. [18][19][20] The most interesting feature of CQD solids is their enormous specific surface area; around one third of the atoms of a few nanometer CQDs are located at the surface, experiencing lower coordination than in bulk. Changing the dielectric or chemical environment thus has a significant effect on the overall properties. Much research has been conducted into this direction as well, leading to the ability to design the properties for applications.Here, we aim to show the most recent developments, put these results in perspective, and identify the limiting factors that limit further improvement in device performance. We focus on lead chalcogenides as they have been the subject of a variety of approaches to form solids, mainly because of their prospects in solar cell applications. However, the fundamental findings reported are valid for CQDs in general, and most methods can be used for other types of semiconductor nanocrystals as well. Although, numerous studies discuss the unique optical properties of CQDs, we have chosen to avoid their discussion here to be able to focus on the fabrication, electronic properties, and applications of CQD assemblies. In Section 2, two novel directions in sample fabrication of lead-chalcogenide CQD assemblies are discussed. The first one, the solution-phase ligand exchange, is relevant for mass production of devices, while the other, the self-assembly, is important for creating arrays with controlled nanostructure and order. Related to the difference in The quest for novel semiconductors with easy, cheap fabrication and tailorable properties has led to the development of several classes of materials, such as semiconducting polymers, carbon nanotubes, hybrid perovskites, and colloidal quantum dots. All these candidates can be processed from the liquid phase, enabling easy fabrication, and are suitable for different electronic and optoelectronic applications. Here, rece...

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PbS Nanoparticles Capped with Tetrathiafulvalenetetracarboxylate: Utilizing Energy Level Alignment for Efficient Carrier Transport

Cited by 45 publications

References 66 publications

Quantifying Angular Correlations between the Atomic Lattice and the Superlattice of Nanocrystals Assembled with Directional Linking

Quantifying Angular Correlations between the Atomic Lattice and the Superlattice of Nanocrystals Assembled with Directional Linking

Towards Photo-Switchable Transport in Quantum Dot Solids

Lead‐Chalcogenide Colloidal‐Quantum‐Dot Solids: Novel Assembly Methods, Electronic Structure Control, and Application Prospects

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