Extremely Slow Spontaneous Electron Trapping in Photodoped <i>n</i>-Type CdSe Nanocrystals

Tsui, Emily Y.; Carroll, Gerard M.; Miller, B.J.; Marchioro, Arianna; Gamelin, Daniel R.

doi:10.1021/acs.chemmater.7b00839

Cited by 32 publications

(79 citation statements)

References 59 publications

(161 reference statements)

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“…21,28 We have also shown that even though midgap electron traps below the Fermi level are filled by photodoping, new midgap traps appear spontaneously on long time scales because of trap-state fluctuations. 21 Following these observations, the trend of increasing 〈 /01 〉 with CdS shell growth is attributed to (1) reduction of the number of midgap surface electron traps through physical passivation, and (2) shifting of the conduction-band edge to more positive redox potentials relative to the electron-trap-state distribution through relaxation of electron quantum confinement. 21 19,21 This slow trapping is manifested as an extremely slow recovery of excitonic absorption after photodoping.…”

Section: Results and Analysismentioning

confidence: 87%

Electron Stability and Negative-Tetron Luminescence in Free-Standing Colloidal n-Type CdSe/CdS Quantum Dots

et al. 2017

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We examine the effects of CdS shell growth on photochemical reduction of colloidal CdSe quantum dots (QDs) and describe the spectroscopic properties of the resulting n-type CdSe/CdS QDs. CdS shell growth greatly slows electron trapping. Because of this improvement, complete two-electron occupancy of the 1S conduction-band orbital is achieved in CdSe/CdS QDs and found to be much more stable than in past experiments. Simultaneous photoluminescence at two different energies is now observed from QDs possessing two excess conduction-band electrons, reflecting competing recombination of discretized 1S and 1P conduction-band electrons within photogenerated four-carrier negative tetrons (three electrons and one hole). Stable occupancy of the 1P level is not achievable under these conditions, and possible reasons are discussed. The stability and accessibility of these multielectron configurations, and the facile spectroscopic detection of negative tetrons, both make photodoped core/shell QDs attractive for exploring the physical properties of free-standing heavily n-doped colloidal CdSe-based QDs.

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Section: Results and Analysismentioning

confidence: 87%

Electron Stability and Negative-Tetron Luminescence in Free-Standing Colloidal n-Type CdSe/CdS Quantum Dots

et al. 2017

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“…When the reduction potential for the anion sublattice is reached (−1.0 V vs Ag PRE), a much larger current density is observed, which we attribute to the reduction of the disulfide bridges in the covellite crystal structure (number of injected electrons: 4.0 × 10 22 cm –3 , see Supporting Information Figure S4). For these hole carrier density calculations, we assume a one-to-one relationship between the number of injected electrons and the hole carrier density, since we do not observe side reactions like reducible defects, 33 as mentioned above. The reduction of the disulfide bridges corresponds to complete filling of their antibonding orbitals making the bonds unstable and causing a change in the overall crystal structure, as shown below.…”

Section: Resultsmentioning

confidence: 99%

Switching between Plasmonic and Fluorescent Copper Sulfide Nanocrystals

et al. 2017

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Control over the doping density in copper sulfide nanocrystals is of great importance and determines its use in optoelectronic applications such as NIR optical switches and photovoltaic devices. Here, we demonstrate that we can reversibly control the hole carrier density (varying from >1022 cm–3 to intrinsic) in copper sulfide nanocrystals by electrochemical methods. We can control the type of charge injection, i.e., capacitive charging or ion intercalation, via the choice of the charge compensating cation (e.g., ammonium salts vs Li+). Further, the type of intercalating ion determines whether the charge injection is fully reversible (for Li+) or leads to permanent changes in doping density (for Cu+). Using fully reversible lithium intercalation allows us to switch between thin films of covellite CuS NCs (Eg = 2.0 eV, hole density 1022 cm–3, strong localized surface plasmon resonance) and low-chalcocite CuLiS NCs (Eg = 1.2 eV, intrinsic, no localized surface plasmon resonance), and back. Electrochemical Cu+ ion intercalation leads to a permanent phase transition to intrinsic low-chalcocite Cu2S nanocrystals that display air stable fluorescence, centered around 1050 nm (fwhm ∼145 meV, PLQY ca. 1.8%), which is the first observation of narrow near-infrared fluorescence for copper sulfide nanocrystals. The dynamic control over the hole doping density and fluorescence of copper sulfide nanocrystals presented in this work and the ability to switch between plasmonic and fluorescent semiconductor nanocrystals might lead to their successful implementation into photovoltaic devices, NIR optical switches and smart windows.

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“…This work shows the importance of NC surface stoichiometry in applications involving tuned NC redox potentials, band‐edge alignment, or electron‐transfer driving forces. Furthermore, Fermi levels and NC redox potentials were measured using this method . The average number of conduction‐band electrons (e CB − ) per NC was also assessed using the absorbance.…”

Section: Advantages In Usementioning

confidence: 99%

“…Furthermore, Fermi levels and NC redox potentials were measured using this method. [112] The average number of conduction-band electrons (e CB À ) per NC was also assessed using the absorbance. Authors reported extremely slow trapping of e CB À in free-standing photodoped colloidal ntype CdSe NCs.…”

Section: Advantages In Usementioning

confidence: 99%

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Spectroelectrochemistry of Quantum Dots

Garoz‐Ruiz

Perales-Rondón

Heras

et al. 2019

Israel Journal of Chemistry

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Spectroelectrochemistry (SEC) is a set of techniques with many advantages in the study and characterization of materials. Although SEC has not yet been widely used to study quantum dots (QDs), the information extracted from SEC experiments about these nanostructures is very useful. Most of the works that use SEC to study QDs are high‐quality pieces of research. This review intends to show how to perform SEC in an easy way and what information can be obtained using these techniques. Most of the examples shown in this review are related to semiconductor and carbon QDs. After a brief introduction, some optoelectronic properties of QDs and the main SEC techniques are described. The capabilities of SEC for the study of QDs are illustrated with examples extracted from literature. Finally, the needs of SEC to become a user‐friendly technique and its evolution to become more powerful are commented in the last section of the review.

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Extremely Slow Spontaneous Electron Trapping in Photodoped n-Type CdSe Nanocrystals

Cited by 32 publications

References 59 publications

Electron Stability and Negative-Tetron Luminescence in Free-Standing Colloidal n-Type CdSe/CdS Quantum Dots

Electron Stability and Negative-Tetron Luminescence in Free-Standing Colloidal n-Type CdSe/CdS Quantum Dots

Switching between Plasmonic and Fluorescent Copper Sulfide Nanocrystals

Spectroelectrochemistry of Quantum Dots

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