Tuning exciton diffusion, mobility and emission line width in CdSe nanoplatelets <i>via</i> lateral size

Achtstein, Alexander W.; Ayari, Sabrine; Helmrich, Sophia; Quick, Michael T.; Owschimikow, Nina; Jaziri, S.; Woggon, U.

doi:10.1039/d0nr04745g

Cited by 13 publications

(15 citation statements)

References 73 publications

(88 reference statements)

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“…While e, h and T undergo true movement, the relative displacement of a bound e and h within the exciton can not transport charge to a similar extent. The excitonic mobility shape is broad as low-frequency transitions (near the intraexcitonic transition continuum) overlap at a dephasing rate of Γ X = 35 ps –1 . However, it is not constant in a typical 0–3 THz observation window, as often claimed.…”

Section: Results and Discussionmentioning

confidence: 85%

Quantum Nature of THz Conductivity: Excitons, Charges, and Trions in 2D Semiconductor Nanoplatelets and Implications for THz Imaging and Solar Hydrogen Generation

Quick

Ayari

Owschimikow

et al. 2022

ACS Appl. Nano Mater.

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As for many technological applications, excitation transport determines their performance, we investigate the THz conductivity of electrons, holes, excitons, and trions in 2D semiconductor nanoparticles. While the non-Drude-like frequency response of charge carriers in these systems has been established recently, the responses of excitons and trions remain not fully understood. We show that the exciton polarizability is related to intraexcitonic transitions between different states of relative motion and independent of the center-of-mass motion of an exciton. In contrast to simplifying models, a thermal distribution among those states leads to a considerable alteration of the resultant polarizability. To understand experimental data, we develop a quantum mechanical model for the mobility of trions and describe a linear-response-based formalism for the polarizability of excitons with a thermal distribution. Discussing the size- and aspect ratio dependent mobility of these species, we show that the particle manifold can be tuned. While for small nanoplatelets and a high number of background electrons signatures of negative trions dominate the THz response, in contrast, for extended 2D systems, excitons prevail. Like the conductance for charge carriers, the polarizability of excitons as well as mobility of trions is altered by quantization effects. Our results give basic insights to the understanding of the THz spectra of colloidal, epitaxial, and free-standing 2D semiconductors, for instance, monolayer perovskites and TMDCs, materials of current interest for solar energy harvesting, photocatalysis, or high bandwidth and low-noise nanoelectronics or THz detection in imaging systems for security applications. We provide a toolbox for the analysis of experiments and improved microscopic understanding, which in reverse allows optimization of technological applications.

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Section: Results and Discussionmentioning

confidence: 85%

Quantum Nature of THz Conductivity: Excitons, Charges, and Trions in 2D Semiconductor Nanoplatelets and Implications for THz Imaging and Solar Hydrogen Generation

Quick

Ayari

Owschimikow

et al. 2022

ACS Appl. Nano Mater.

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“…For Γ we chose typical dephasing rates of 8•10 11 s −1 at 10 K and 5•10 13 s −1 at 300 K in CdSe. 24 The frequency range of 0 -3 THz reflects typical settings of Terahertz Time Domain Spectroscopy (THz-TDS). 25,26 Due to the similar effective masses there are no considerable differences in the electron (continuous lines) and hole (dotted lines) mobilities.…”

Section: Resultsmentioning

confidence: 99%

Population dependence of THz charge carrier mobility and non-Drude-like behavior in short semiconductor nanowires

2022

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“…To investigate how the different hopping rates and interparticle distances affect the overall exciton diffusion, we look at the basics of the FRET process, according to which an increased temperature should enhance the hopping rate. 9,33 Therefore, we constructed a simple stage with a coupled Peltier device to control the temperature of the films and study the effect on the diffusion parameters. The accessible temperature range is limited to 15−55 °C, as at lower temperatures, the moisture from the ambient air condenses on the samples, while at higher temperatures, the NC films begin to degrade irreversibly.…”

Section: Resultsmentioning

confidence: 99%

Electron–Hole Binding Governs Carrier Transport in Halide Perovskite Nanocrystal Thin Films

et al. 2022

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Two-dimensional halide perovskite nanoplatelets (NPLs) have exceptional light-emitting properties, including wide spectral tunability, ultrafast radiative decays, high quantum yields (QY), and oriented emission. To realize efficient devices, it is imperative to understand how exciton 2 transport progresses in NPL thin films. Due to the high binding energies of electron-hole pairs, excitons are generally considered the dominant species responsible for carrier transfer. We employ spatially and temporally resolved optical microscopy to map exciton diffusion in perovskite nanocrystal (NC) thin films between 15 °𝐶 and 50 °𝐶. At room temperature (RT), we find the diffusion length to be inversely correlated to the thickness of the nanocrystals (NCs). With increasing temperatures, exciton diffusion declines for all NC films, but at different rates. This leads to specific temperature turnover points, at which thinner NPLs exhibit higher diffusion lengths. We attribute this anomalous diffusion behavior to the coexistence of excitons and free electron hole-pairs inside the individual NCs within our temperature range. The organic ligand shell surrounding the NCs prevents charge transfer. Accordingly, any time an electron-hole pair spends in the unbound state reduces the FRET-mediated inter-NC transfer rates and consequently the overall diffusion. These results clarify how exciton diffusion progresses in strongly confined halide perovskite NC films, emphasizing critical considerations for optoelectronic devices.

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Tuning exciton diffusion, mobility and emission line width in CdSe nanoplatelets via lateral size

Abstract: We investigate the lateral size tunability of the exciton diffusion coefficient and mobility in colloidal quantum wells by the means of line width analysis and theoretical modeling. We show that...

Cited by 13 publications

References 73 publications

Quantum Nature of THz Conductivity: Excitons, Charges, and Trions in 2D Semiconductor Nanoplatelets and Implications for THz Imaging and Solar Hydrogen Generation

Quantum Nature of THz Conductivity: Excitons, Charges, and Trions in 2D Semiconductor Nanoplatelets and Implications for THz Imaging and Solar Hydrogen Generation

Population dependence of THz charge carrier mobility and non-Drude-like behavior in short semiconductor nanowires

Electron–Hole Binding Governs Carrier Transport in Halide Perovskite Nanocrystal Thin Films

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