Challenge to the deep-trap model of the surface in semiconductor nanocrystals

Mooney, Jonathan; Krause, Michael; Saari, Jonathan I.; Kambhampati, Patanjali

doi:10.1103/physrevb.87.081201

Cited by 139 publications

(253 citation statements)

References 37 publications

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“…3(a) and 3(b) [52]. Observations of such radiative trap states confirm previous reports [53,54]. Using both time-resolved photoluminescence (TRPL) and transient absorption (TA) measurements we further quantified the lifetime of the trap states as being longer than microseconds (Figs.…”

Section: Origins Of Hole Trapssupporting

confidence: 77%

Ultrafast photoinduced dynamics in quantum dot-based systems for light harvesting

et al. 2015

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KEYWORDScolloidal quantum dots, electron transfer, energy transfer, core shell quantum dots, quantum dot solar cell ABSTRACT Colloidal semiconductor nanocrystals, referred to as quantum dots, offer simple low-temperature solution-based methods for constructing optoelectronic devices such as light emitting diodes and solar cells. We review recent progress in the understanding of photoinduced processes in key components of a certain type of quantum dot solar cells where the dots sensitize a suitable metal oxide, such as ZnO or TiO 2 , for electron injection, and NiO for hole injection. The electron and hole injection dynamics are discussed in detail as a function of the quantum dot size and core-shell structure, the linker molecule type, and the morphology of the accepting metal oxide. Hole trapping is identified as a major factor limiting the performance of quantum dot-based devices. We review possible strategies for improvement that use core-shell structures and directed excitation energy transfer between quantum dots. Finally, the generation and injection of multiple excitons are revisited. We show that the assumption of a linear relationship between the intensity of transient absorption signal and the number of excitons does not generally hold, and this observation can partially explain highly disparate results for the efficiency of generating multiple excitons. A consistent calculation procedure for studies of multiple exciton generation is provided. Finally, we offer a brief personal outlook on the topic.

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Section: Origins Of Hole Trapssupporting

confidence: 77%

Ultrafast photoinduced dynamics in quantum dot-based systems for light harvesting

et al. 2015

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“…According to the literature, [25][26]29 we refer to carrier trapping as a charge-transfer process, resulting in localized charges whose excess energy is slowly and non-radiatively released via coupling to ligand vibrations. Nevertheless, the effect of carrier trapping on PLQY is twofold.…”

Section: Figure 2 -Scheme Representing the Evolution Of Excited Statementioning

confidence: 99%

“…Only few works have hitherto focused on the interplay between charge trapping at the different interfaces and their effect on QDs optical properties. [25][26][27] Recently, our group reported on the effect of trapping on PL dynamics in core/shell CdSe/CdxZn1-xS QDs. 28 We interpreted transient PL (TRPL) data formulating a phenomenological model, comprising the balance between charge trapping and de-trapping processes.…”

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confidence: 99%

Bridging Energetics and Dynamics of Exciton Trapping in Core–Shell Quantum Dots

2016

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The widespread application of quantum dots greatly profits from their broad absorption band.However, the variable nature of excitations within these bands is expected to result in undesired excitation energy dependence of steady state emission properties. We demonstrate the different role played by hot and cold carrier trapping in determining fluorescence quantum yields. Our analysis relates the energetic parameters with the available knowledge on the dynamics of charge trapping. It turns out that de-trapping processes play a pivotal role in determining steady state emission properties. We studied excitation dependent photoluminescence quantum yields (PLQY) in different CdSe/CdxZn1-xS (x = 0, 0.5, 1) quantum dots to identify best performing heterostructures, in terms of shell thickness and composition. Our rationalization of the observed behavior is focused on the modulation of trapping and de-trapping rates. The combination of experimental results and PLQY kinetics modeling reveals the need to consider hot-carrier trapping, supporting recent 2 dynamics observations. This work provides a deeper insight into trapping process in quantum dots, relating its energetics and dynamics.

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“…[1][2][3][4][5][6][7][8][9][10] However, due to high surface-to-volume ratio of these NCs, the large number of unpassivated atoms on their surfaces lead to the formation of highly dense trap states, which serve as undesirable, non-radiative deactivation channels for photo-generated charge carriers. [11][12][13][14][15] This often acts as a bottleneck in the use of these NCs for photoactive applications. Typically, multinary metal chalcogenides possess many desirable attributes, such as high absorption coefficient and high photo-stability for optoelectronic applications, [16][17][18][19][20][21] and a record power conversion efficiency of 21.7% has been obtained in the bulk form following physical deposition techniques, 22 which is close to the efficiency of polycrystalline silicon solar cells.…”

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confidence: 99%

Real-Space Mapping of Surface Trap States in CIGSe Nanocrystals Using 4D Electron Microscopy

et al. 2016

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Surface trap states in copper indium gallium selenide semiconductor nanocrystals (NCs), which serve as undesirable channels for nonradiative carrier recombination, remain a great challenge impeding the development of solar and optoelectronics devices based on these NCs. In order to design efficient passivation techniques to minimize these trap states, a precise knowledge about the charge carrier dynamics on the NCs surface is essential. However, selective mapping of surface traps requires capabilities beyond the reach of conventional laser spectroscopy and static electron microscopy; it can only be accessed by using a one-of-a-kind, second-generation four-dimensional scanning ultrafast electron microscope (4D S-UEM) with subpicosecond temporal and nanometer spatial resolutions. Here, we precisely map the collective surface charge carrier dynamics of copper indium gallium selenide NCs as a function of the surface trap states before and after surface passivation in real space and time using S-UEM. The time-resolved snapshots clearly demonstrate that the density of the trap states is significantly reduced after zinc sulfide (ZnS) shelling. Furthermore, the removal of trap states and elongation of carrier lifetime are confirmed by the increased photocurrent of the self-biased photodetector fabricated using the shelled NCs.

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Challenge to the deep-trap model of the surface in semiconductor nanocrystals

Cited by 139 publications

References 37 publications

Ultrafast photoinduced dynamics in quantum dot-based systems for light harvesting

Ultrafast photoinduced dynamics in quantum dot-based systems for light harvesting

Bridging Energetics and Dynamics of Exciton Trapping in Core–Shell Quantum Dots

Real-Space Mapping of Surface Trap States in CIGSe Nanocrystals Using 4D Electron Microscopy

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