Charge transport and localization in atomically coherent quantum dot solids

Whitham, Kevin; Yang, Jun; Savitzky, Benjamin H.; Kourkoutis, Lena F.; Wise, Frank W.; Hanrath, Tobias

doi:10.1038/nmat4576

Cited by 267 publications

(423 citation statements)

References 36 publications

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“…[17][18][19][20][21][22][23] The inherent large surface-to-volume ratio of QD materials results in unsaturated dangling bonds, creating undesired electronic trap states within the bandgap of QD solids. The ligand exchange procedure itself is prone to create new, rather than passivate existing, dangling bonds.…”

mentioning

confidence: 99%

10.6% Certified Colloidal Quantum Dot Solar Cells via Solvent-Polarity-Engineered Halide Passivation

et al. 2016

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Colloidal quantum dot (CQD) solar cells are solution-processed photovoltaics with broad spectral absorption tunability. Major advances in their efficiency have been made via improved CQD surface passivation and device architectures with enhanced charge carrier collection. Herein, we demonstrate a new strategy to improve further the passivation of CQDs starting from the solution phase. A cosolvent system is employed to tune the solvent polarity in order to achieve the solvation of methylammonium iodide (MAI) and the dispersion of hydrophobic PbS CQDs simultaneously in a homogeneous phase, otherwise not achieved in a single solvent. This process enables MAI to access the CQDs to confer improved passivation. This, in turn, allows for efficient charge extraction from a thicker photoactive layer device, leading to a certified solar cell power conversion efficiency of 10.6%, a new certified record in CQD photovoltaics.

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confidence: 99%

10.6% Certified Colloidal Quantum Dot Solar Cells via Solvent-Polarity-Engineered Halide Passivation

et al. 2016

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“…In the n-channel operation, the drain current remarkably increases with the temperature, indicating that electron transport in PbSe NR assemblies is thermally activated (hopping transport). [33] Negligible hysteresis is observed between forward and reverse scan in the n-channel transfer characteristics at temperatures between 240 and 60 K, while a distinct hysteresis appears above 240 K and a small hysteresis is reappearing below 60 K (Figure 4 and Figure S7, Supporting Information). In the p-channel operation, the drain current also increases with increasing temperature with some fluctuation, but the large hysteretic behavior remains over the whole temperature range showing a decrease at low temperature.…”

Section: Resultsmentioning

confidence: 99%

“…[27] Moreover, the presence of trap states, which may stem from (i) the synthetic process; (ii) the ligand-exchange during fabrication; (iii) adsorption of molecules (e.g., water and oxygen) at the interface between the active layer and gate dielectric, [28] is responsible for not ideal transport properties. Again, while a large number of papers discuss results on PbS and PbSe spherical QDs, [12,[29][30][31][32][33] very little is known on PbSe rods charge transport properties.…”

Section: Introductionmentioning

confidence: 99%

PbSe Nanorod Field‐Effect Transistors: Room‐ and Low‐Temperature Performance

Han

Balazs

Shulga

et al. 2018

Adv Elect Materials

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Bohr radius, quantum confinement effects emerge, the bandgap energy increases, and discrete energy levels appear in the density of states spectrum. From this point of view, PbSe is of particular interest for its large exciton Bohr radius (46 nm) and equal electron and hole effective masses, [7] which allows to achieve strong confinement even in relatively large particles. Moreover, PbSe has a narrow bandgap (0.28 eV in bulk), [8] with consequent optical activity in the near infrared spectral range [9] and displays a high dielectric constant (ε m = 23). [10] These versatile characteristics make PbSe QDs promising semiconductor building blocks for photovoltaic devices, [11] electronic circuits, [12] and mid-and near-infrared sensing. [13] Moreover, it has been demonstrated that the dimensionality of the nanostructure, in practice the aspect ratio, allows for tuning the physical properties. For example, quasi-1D PbSe nanorods (NRs) have been reported to exhibit more efficient electron transport, [14] enhanced multiple exciton generation, [15,16] reduced Auger recombination rates, [17] higher absorption coefficient, [18] and longer biexciton lifetime [19] relative to PbSe QDs. More recently, a maximum external quantum efficiency of 122% has been reported in PbSe NR solar cells. [15] Despite the prospects for high-performance PbSe NR solar cells, [15,20] there is still a lack of studies about their transport properties. This is especially surprising as due to their 1D confinement higher mobilities than in QDs can be expected. The fabrication of thinfilm FETs is a useful method for studying charge transport properties in solution-processed semiconductors, such as QDs.During synthesis colloidal QDs are capped with long-alkyl chain ligands, which provide solubility and stability in solution but also suppress charge carrier transport when the QDs are assembled in films. Ligand exchange with short molecules that can decrease the inter-QD spacing and passivate surface traps is essential for the fabrication of high performing devices. The choice of ligands largely depends on the desired QD properties. In early works, amines (especially hydrazine) were used for PbSe QD and nanowire-based transistors. [21,22] To cross-link PbSe QD films, a series of short-chain bifunctional molecules (e.g., 1,2-ethanedithiol, [23] 1,3-benzenedithiol, [24] 3-mercaptopropionic acid [25] etc.) were introduced in device fabrication. Most recently, the use of halide ions (Cl − , Br− ) have led to rapid improvements in PbS/PbSe QD solar cell power conversion efficiencies (up to 11.3%) and long-term stability in air. [1,26] The proposed

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“…Recently, Whitham et al . [151] demonstrated that charge localization can be greatly suppressed by reducing the level of disorder in CQD films, by epitaxially connecting ordered PbSe nanocrystals.…”

Section: Quantum Dots For Photovoltaic Applicationmentioning

confidence: 99%

Understanding chemically processed solar cells based on quantum dots

Malgras

Nattestad

Kim

et al. 2017

Science and Technology of Advanced Materials

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Photovoltaic energy conversion is one of the best alternatives to fossil fuel combustion. Petroleum resources are now close to depletion and their combustion is known to be responsible for the release of a considerable amount of greenhouse gases and carcinogenic airborne particles. Novel third-generation solar cells include a vast range of device designs and materials aiming to overcome the factors limiting the current technologies. Among them, quantum dot-based devices showed promising potential both as sensitizers and as colloidal nanoparticle films. A good example is the p-type PbS colloidal quantum dots (CQDs) forming a heterojunction with a n-type wide-band-gap semiconductor such as TiO2 or ZnO. The confinement in these nanostructures is also expected to result in marginal mechanisms, such as the collection of hot carriers and generation of multiple excitons, which would increase the theoretical conversion efficiency limit. Ultimately, this technology could also lead to the assembly of a tandem-type cell with CQD films absorbing in different regions of the solar spectrum.

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Charge transport and localization in atomically coherent quantum dot solids

Cited by 267 publications

References 36 publications

10.6% Certified Colloidal Quantum Dot Solar Cells via Solvent-Polarity-Engineered Halide Passivation

10.6% Certified Colloidal Quantum Dot Solar Cells via Solvent-Polarity-Engineered Halide Passivation

PbSe Nanorod Field‐Effect Transistors: Room‐ and Low‐Temperature Performance

Understanding chemically processed solar cells based on quantum dots

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