Enhanced Hot-Carrier Cooling and Ultrafast Spectral Diffusion in Strongly Coupled PbSe Quantum-Dot Solids

Gao, Yunan; Talgorn, Elise; Aerts, Michiel; Trinh, M. Tuan; Schins, Juleon M.; Houtepen, Arjan J.; Siebbeles, Laurens D. A.

doi:10.1021/nl203235u

Cited by 72 publications

(105 citation statements)

References 37 publications

(64 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Both are likely to occur simultaneously in NC solids (e.g., trapmediated recombination). Here, we assume that the decrease in photoconductivity is well-modeled by the recombination of electronÀhole pairs because carrier relaxation is rapid 21,52 and both recombination and trapping of charge carriers ; removal from highmobility states ; have similar results on the effective carrier concentration and the terahertz transmission.…”

Section: Resultsmentioning

confidence: 99%

Lifetime, Mobility, and Diffusion of Photoexcited Carriers in Ligand-Exchanged Lead Selenide Nanocrystal Films Measured by Time-Resolved Terahertz Spectroscopy

et al. 2015

View full text Add to dashboard Cite

Colloidal semiconductor nanocrystals have been used as building blocks for electronic and optoelectronic devices ranging from field-effect transistors to solar cells. Properties of the nanocrystal films depend sensitively on the choice of capping ligand to replace the insulating synthesis ligands. Thus far, ligands leading to the best performance in transistors result in poor solar cell performance, and vice versa. To gain insight into the nature of this dichotomy, we used time-resolved terahertz spectroscopy measurements to study the mobility and lifetime of PbSe nanocrystal films prepared with five common ligand-exchange reagents. Noncontact terahertz spectroscopy measurements of conductivity were corroborated by contacted van der Pauw measurements of the same samples. The films treated with different displacing ligands show more than an order of magnitude difference in the peak conductivities and a bifurcation of time dynamics. Inorganic chalcogenide ligand exchanges with sodium sulfide (Na2S) or ammonium thiocyanate (NH4SCN) show high mobilities but nearly complete decay of transient photocurrent in 1.4 ns. In contrast, ligand exchanges with 1,2-ethylenediamine (EDA), 1,2-ethanedithiol (EDT), and tetrabutylammonium iodide (TBAI) show lower mobilities but longer carrier lifetimes, resulting in longer diffusion lengths. This bifurcated behavior may explain the divergent performance of field-effect transistors and photovoltaics constructed from nanocrystal building blocks with different ligand exchanges.

show abstract

Section: Resultsmentioning

confidence: 99%

Lifetime, Mobility, and Diffusion of Photoexcited Carriers in Ligand-Exchanged Lead Selenide Nanocrystal Films Measured by Time-Resolved Terahertz Spectroscopy

et al. 2015

View full text Add to dashboard Cite

show abstract

“…Figure 5a depicts the quantity S(t) = Φ e (t)μ e + Φ h (t)μ h , as a function of time, t, after photoexcitation, which is the sum of the product of the quantum yield of electrons, Φ e (t) and holes, Φ h (t), and the real mobility component of their mobility, (μ e and μ h ). At early times, the real THz conductivity exhibits a fast decay at times ≤ 4 ps, which is assigned to relaxation of highly mobile hot charges to the band edge, where the mobility is lower [7,[22][23][24]. After 4 ps, S(t) is as high as 20 ± 2 cm 2 /Vs.…”

Section: Terahertz (Thz) Spectroscopy/conductivitymentioning

confidence: 99%

Ultrafast Transient Absorption and Terahertz Spectroscopy as Tools to Probe Photoexcited States and Dynamics in Colloidal 2D Nanostructures

Lauth

Kinge

Siebbeles

2016

Zeitschrift Für Physikalische Chemie

View full text Add to dashboard Cite

Two-dimensional (2D) semiconductors hold high potential for the implementation of efficient ultrathin electronics (e.g. field-effect transistors, light emitting diodes and solar cell devices). In recent years, colloidal methods to synthesize ultrathin 2D materials have been developed that offer alternatives (like the production of non-layered 2D materials and upscaling) to mechanical exfoliation methods. By focusing on optoelectronic applications, it is important to characterize the nature and dynamics of photoexcited states in these materials. In this paper, we use ultrafast transient absorption (TA) and terahertz (THz) spectroscopy as optimal tools for such a characterization. We choose recently synthesized ultrathin colloidal 2D InSe nanosheets (inorganic layer thickness 0.8-1.7 nm; ≤ 5 nm including ligands) for discussing TA and THz spectroscopic studies and elucidate their charge carrier dynamics under photoexcitation with TA. THz spectroscopy is then used to extract contactless AC mobilities as high as 20 ± 2 cm 2 /Vs in single InSe layers. The obtained results underpin the general applicability of TA and THz spectroscopy for characterizing photoexcited states in 2D semiconductors.

show abstract

“…For example, the increased interparticle coupling and greater electrical conductivity previously demonstrated in these SCN exchanged samples 13 likely increase exciton and charge carrier diffusion to lower energy QDs. 27 Recent room temperature studies of QD solids demonstrated that excitons can become concentrated at low energy "hotspots", enabling multiexciton phenomena when excitation densities surpass a rather low threshold of 10 À3 excitons per quantum dot. 66 Under these conditions, which are met in this study, Auger processes can produce fast, radiationless recombination as well as hot carrier generation that enhances the likelihood of carrier trapping.…”

Section: Resultsmentioning

confidence: 99%

Ultrafast Electron Trapping in Ligand-Exchanged Quantum Dot Assemblies

et al. 2015

View full text Add to dashboard Cite

We use time-integrated and time-resolved photoluminescence and absorption to characterize the low-temperature optical properties of CdSe quantum dot solids after exchanging native aliphatic ligands for thiocyanate and subsequent thermal annealing. In contrast to trends established at room temperature, our data show that at low temperature the band-edge absorptive bleach is dominated by 1S3/2h hole occupation in the quantum dot interior. We find that our ligand treatments, which bring enhanced interparticle coupling, lead to faster surface state electron trapping, a greater proportion of surface-related photoluminescence, and decreased band-edge photoluminescence lifetimes.

show abstract

Enhanced Hot-Carrier Cooling and Ultrafast Spectral Diffusion in Strongly Coupled PbSe Quantum-Dot Solids

Cited by 72 publications

References 37 publications

Lifetime, Mobility, and Diffusion of Photoexcited Carriers in Ligand-Exchanged Lead Selenide Nanocrystal Films Measured by Time-Resolved Terahertz Spectroscopy

Lifetime, Mobility, and Diffusion of Photoexcited Carriers in Ligand-Exchanged Lead Selenide Nanocrystal Films Measured by Time-Resolved Terahertz Spectroscopy

Ultrafast Transient Absorption and Terahertz Spectroscopy as Tools to Probe Photoexcited States and Dynamics in Colloidal 2D Nanostructures

Ultrafast Electron Trapping in Ligand-Exchanged Quantum Dot Assemblies

Contact Info

Product

Resources

About