Light-Driven and Phonon-Assisted Dynamics in Organic and Semiconductor Nanostructures

Kilina, Svetlana; Kilin, Dmitri S.; Tretiak, Sergei

doi:10.1021/acs.chemrev.5b00012

Cited by 169 publications

(212 citation statements)

References 527 publications

(699 reference statements)

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“…[65][66][67] Shown in Figure 7, the FTs indicate that many more modes contribute to dephasing in bare Cd 33 Se 33 compared to that in passivated 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60…”

Section: Phonon Modesmentioning

confidence: 99%

Ligands Slow Down Pure-Dephasing in Semiconductor Quantum Dots

et al. 2015

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It is well-known experimentally and theoretically that surface ligands provide additional pathways for energy relaxation in colloidal semiconductor quantum dots (QDs). They increase the rate of inelastic charge-phonon scattering and provide trap sites for the charges. We show that, surprisingly, ligands have the opposite effect on elastic electron-phonon scattering. Our simulations demonstrate that elastic scattering slows down in CdSe QDs passivated with ligands compared to that in bare QDs. As a result, the pure-dephasing time is increased, and the homogeneous luminescence line width is decreased in the presence of ligands. The lifetime of quantum superpositions of single and multiple excitons increases as well, providing favorable conditions for multiple excitons generation (MEG). Ligands reduce the pure-dephasing rates by decreasing phonon-induced fluctuations of the electronic energy levels. Surface atoms are most mobile in QDs, and therefore, they contribute greatly to the electronic energy fluctuations. The mobility is reduced by interaction with ligands. A simple analytical model suggests that the differences between the bare and passivated QDs persist for up to 5 nm diameters. Both low-frequency acoustic and high-frequency optical phonons participate in the dephasing processes in bare QDs, while low-frequency acoustic modes dominate in passivated QDs. The theoretical predictions regarding the pure-dephasing time, luminescence line width, and MEG can be verified experimentally by studying QDs with different surface passivation.

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Section: Phonon Modesmentioning

confidence: 99%

Ligands Slow Down Pure-Dephasing in Semiconductor Quantum Dots

et al. 2015

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“…Such organic π-conjugated semiconductors have striking and rather complex optical properties. Their optical excitation not only results in the formation of excitons, Coulomb bound electron-hole pairs, but—in contrast to, for example, inorganic semiconductors—also in the creation of a wealth of other quasiparticles, namely polaron pairs, polarons, biexcitons and others91011. Polaron pairs, sometimes also called spatially indirect or charge-transfer excitons, are charge-neutral excitations in which spatially separated electrons and holes weakly interact via their Coulomb attraction and are each coupled to their own lattice distortion.…”

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confidence: 99%

Tracking the coherent generation of polaron pairs in conjugated polymers

et al. 2016

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The optical excitation of organic semiconductors not only generates charge-neutral electron-hole pairs (excitons), but also charge-separated polaron pairs with high yield. The microscopic mechanisms underlying this charge separation have been debated for many years. Here we use ultrafast two-dimensional electronic spectroscopy to study the dynamics of polaron pair formation in a prototypical polymer thin film on a sub-20-fs time scale. We observe multi-period peak oscillations persisting for up to about 1 ps as distinct signatures of vibronic quantum coherence at room temperature. The measured two-dimensional spectra show pronounced peak splittings revealing that the elementary optical excitations of this polymer are hybridized exciton-polaron-pairs, strongly coupled to a dominant underdamped vibrational mode. Coherent vibronic coupling induces ultrafast polaron pair formation, accelerates the charge separation dynamics and makes it insensitive to disorder. These findings open up new perspectives for tailoring light-to-current conversion in organic materials.

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“…So, additionally one needs to compute exciton relaxation times due to phonon emission, and, then, contributions to R 1 , R 2 from decays of a photon into low-energy excitons. At the atomistic level, this task can be achieved by employing the finite temperature/real time technique of perturbative many-body quantum mechanics [102][103][104], or the reduced density matrix method [76,[105][106][107].…”

Section: Discussionmentioning

confidence: 99%

Enhanced multiple exciton generation in amorphous silicon nanowires and films

Kryjevski

Kilin

2015

Molecular Physics

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KEYWORDSMultiple exciton generation; density functional theory; silicon nanowire; amorphous silicon nanoparticle; silicon quantum dot ABSTRACT Multiple exciton generation (MEG) in nanometer-sized hydrogen-passivated silicon nanowires (NWs), and quasi two-dimensional nanofilms depends strongly on the degree of the core structural disorder as shown by the perturbative many-body quantum mechanics calculations based on the density functional theory simulations. Working to the second order in the electron-photon coupling and in the screened Coulomb interaction, we calculate quantum efficiency (QE), the average number of excitons created by a single absorbed photon, in the Si 29 H 36 quantum dots (QDs) with crystalline and amorphous core structures, simple cubic three-dimensional arrays constructed from these QDs, crystalline and amorphous NWs, and quasi two-dimensional silicon nanofilms, also both crystalline and amorphous. Efficient MEG with QE ranging from 1.3 up to 1.8 at the photon energy of about 3E g , where E g is the electronic gap, is predicted in these nanoparticles except for the crystalline NW and crystalline film where QE 1. MEG in the amorphous nanoparticles is enhanced by the electron localisation due to structural disorder. Combined with the lower gaps, the nanometer-sized amorphous silicon NWs and films are predicted to have effective carrier multiplication within the solar spectrum range..

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Light-Driven and Phonon-Assisted Dynamics in Organic and Semiconductor Nanostructures

Cited by 169 publications

References 527 publications

Ligands Slow Down Pure-Dephasing in Semiconductor Quantum Dots

Ligands Slow Down Pure-Dephasing in Semiconductor Quantum Dots

Tracking the coherent generation of polaron pairs in conjugated polymers

Enhanced multiple exciton generation in amorphous silicon nanowires and films

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