Picosecond Time Resolved Electron Injection from Excited Cresyl Violet Monomers and Cd3P2 Quantum Dots into TiO2

Kietzmann, R.; Willig, F.; Weller, Horst; Vogel, R.; Nath, Dilip C.; Eichberger, Rainer; Liska, Paul; Lehnert, J.

doi:10.1080/00268949108041162

Cited by 44 publications

(39 citation statements)

References 23 publications

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“…The first study was reported in 1991 [12], i.e., shortly after the discovery of dye-sensitized solar cells, which inspired the idea of using QD-MO heterojunctions. Naturally, electron injection in such heterojunctions has since been extensively studied.…”

Section: Electron Injection From Qd To Momentioning

confidence: 98%

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: Electron Injection From Qd To Momentioning

confidence: 98%

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

et al. 2015

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“…The metal oxides differ significantly in their band gaps (TiO 2 % 3.2 eV and Al 2 O 3 % 8-9.9 eV) and in the position of their conduction band edge [2,[39][40][41] Therefore, ET should only be possible when alizarin is coupled to a TiO 2 mesoporous film, while the alizarin/Al 2 O 3 coupled system can serve as a nonreactive reference. In previous studies [18,19,22,23,42,43] the Al 2 O 3 insulator was used as a nonreactive reference system for the investigation of interfacial ET in dye/semiconductor couples. However, despite its huge band gap, ET from the longlived metal-to-ligand charge-transfer state of RuN3 to surface states in the band gap of an Al 2 O 3 thin film was observed by Lian and co-workers.…”

Section: Introductionmentioning

confidence: 99%

“…However, despite its huge band gap, ET from the longlived metal-to-ligand charge-transfer state of RuN3 to surface states in the band gap of an Al 2 O 3 thin film was observed by Lian and co-workers. [19,42] Herein, time-resolved femtosecond absorbance spectroscopy was used to study the dynamics in the alizarin/metal oxide systems. Interestingly, the observed interfacial ET dynamics vary significantly from the dynamics for the alizarin/TiO 2 coupled system in solution obtained in earlier investigations.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast Photoinduced Processes in Alizarin‐Sensitized Metal Oxide Mesoporous Films

2009

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Close to the edge: Photoexcitation of alizarin coupled to the surface of mesoporous TiO(2) films leads to ultrafast electron transfer to the TiO(2) conduction band (see picture). Complex kinetics after photoexcitation depend on the excitation energy, and indicate a position of the alizarin excited state close to the TiO(2) conduction band edge, where the density of acceptor states is reduced. The photoinduced dynamics in Al(2)O(3) and TiO(2) mesoporous films sensitized by the strongly coupled alizarin dye is investigated by femtosecond transient absorption spectroscopy in the spectral range from UV to mid-IR. Alizarin/Al(2)O(3) acts as a nonreactive reference system, in which no electron transfer is observed. For comparison, the photoexcitation of the alizarin dye coupled to the surface of TiO(2) films leads to ultrafast electron transfer from the dye to the TiO(2) conduction band on the sub-100-fs timescale. We observe a fast relaxation of the alizarin excited state as well as a fast recombination of injected electrons with the alizarin cation on the picosecond timescale, which gives rise to very complex kinetics at short delay times. The infrared measurements clearly indicate that trapping of injected electrons is the main mechanism responsible for the observed long-lived charge separation in TiO(2) mesoporous films. The experimental findings can be explained by a position of the dye excited state close to the conduction band edge.

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“…31 Therefore, this long lifetime observed in Cd 3 As 2 QDs permits an increased possibility of charge carrier extraction in solar cells or optoelectronic applications lending it a wide potential applicability. 32 …”

Section: ■ Results and Discussionmentioning

confidence: 97%

Band-Emission Evolutions from Magic-sized Clusters to Nanosized Quantum Dots of Cd₃As₂ in the Hot-Bubbling Synthesis

et al. 2015

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In this work, the band-emissions of both the magic-sized clusters (MSCs) and nanosized quantum dots (QDs) of cadmium arsenide (Cd 3 As 2 ) are studied versus time during the hot-bubbling synthesis. The syntheses are performed by introducing the ex-situ produced H 3 As into the hot-surfactant solutions dissolved with cadmium oleate and ligand molecules. It is found that the MSCs are produced within 4.0 min because of the color change of the solution. However, these clusters are not stable, and the peak of the photoabsorption shifts from 528 to 540 nm with the growth time. Across a shallow energy barrier, the MSCs grow into nanosized quantum dots whose photoluminescence wavelengths are found to extend into the NIR region (λ > 1480 nm) after a growth period of ∼45.0 min. The quantum yield of the band emissions ranges 2.5−8.0% during the growth of Cd 3 As 2 QDs. Analyses from the time-resolved fluorescence decay profiles suggest that the ultrafast exciton radiative decays are the dominant recombination in the Cd 3 As 2 MSCs, and the lifetime is about 0.69 ns. Longer lifetime emissions (200−300 ns) are found in the nanosized QDs, which is ascribed to the delocalized excitons in the lowest QD state after thermalization. This research highlights the origin and evolution of band-emissions in Cd 3 As 2 QDs, which gives an indepth understanding of the electronic structures of Cd 3 As 2 QDs, and thus lending them wider potential applicability. ■ INTRODUCTIONAlthough Cd 3 As 2 is one of the most dangerous compounds, yet it has many promising properties especially in applications as the near-infrared (NIR) photoresponse materials because it has a narrow band gap (∼0.14 eV), 1−3 relatively high dielectric constant (16−36), 4 large Bohr radius of excitons (∼47 nm), large effective mass difference between that of the electron and the hole, 5 and a widely tunable electronic structure. 6 It has been discovered that nanosized Cd 3 As 2 crystals (NCs) or the socalled quantum dots (QDs) exhibit prominent quantum confinement effects as the size decreases. 7 Due to the huge difference in the effective mass of the electron (m n * = 0.035− 0.076m o , m o = 9.31 × 10 −31 kg) and hole (m h * = 0.12m o ), one may tune the conduction band position of Cd 3 As 2 QDs easier than that of the valence band, which makes Cd 3 As 2 an ideal candidate as used in the full-band spectral response photovoltaics 8 and telecommunication devices (λ = 1.3−1.5 μm). 9,10

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Picosecond Time Resolved Electron Injection from Excited Cresyl Violet Monomers and Cd₃P₂ Quantum Dots into TiO₂

Cited by 44 publications

References 23 publications

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

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

Ultrafast Photoinduced Processes in Alizarin‐Sensitized Metal Oxide Mesoporous Films

Band-Emission Evolutions from Magic-sized Clusters to Nanosized Quantum Dots of Cd₃As₂ in the Hot-Bubbling Synthesis

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Picosecond Time Resolved Electron Injection from Excited Cresyl Violet Monomers and Cd3P2 Quantum Dots into TiO2

Cited by 44 publications

References 23 publications

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

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

Ultrafast Photoinduced Processes in Alizarin‐Sensitized Metal Oxide Mesoporous Films

Band-Emission Evolutions from Magic-sized Clusters to Nanosized Quantum Dots of Cd3As2 in the Hot-Bubbling Synthesis

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Product

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Picosecond Time Resolved Electron Injection from Excited Cresyl Violet Monomers and Cd₃P₂ Quantum Dots into TiO₂

Band-Emission Evolutions from Magic-sized Clusters to Nanosized Quantum Dots of Cd₃As₂ in the Hot-Bubbling Synthesis