| 1. |
- Finkelstein-Shapiro, Daniel, et al.
(författare)
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Non-Hermitian Hamiltonians for linear and nonlinear optical response : A model for plexcitons
- 2023
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 158:10
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Tidskriftsartikel (refereegranskat)abstract
- In polaritons, the properties of matter are modified by mixing the molecular transitions with light modes inside a cavity. Resultant hybrid light-matter states exhibit energy level shifts, are delocalized over many molecular units, and have a different excited-state potential energy landscape, which leads to modified exciton dynamics. Previously, non-Hermitian Hamiltonians have been derived to describe the excited states of molecules coupled to surface plasmons (i.e., plexcitons), and these operators have been successfully used in the description of linear and third order optical response. In this article, we rigorously derive non-Hermitian Hamiltonians in the response function formalism of nonlinear spectroscopy by means of Feshbach operators and apply them to explore spectroscopic signatures of plexcitons. In particular, we analyze the optical response below and above the exceptional point that arises for matching transition energies for plasmon and molecular components and study their decomposition using double-sided Feynman diagrams. We find a clear distinction between interference and Rabi splitting in linear spectroscopy and a qualitative change in the symmetry of the line shape of the nonlinear signal when crossing the exceptional point. This change corresponds to one in the symmetry of the eigenvalues of the Hamiltonian. Our work presents an approach for simulating the optical response of sublevels within an electronic system and opens new applications of nonlinear spectroscopy to examine the different regimes of the spectrum of non-Hermitian Hamiltonians.
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| 2. |
- Fresch, Elisa, et al.
(författare)
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Two-dimensional electronic spectroscopy
- 2023
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Ingår i: Nature Reviews Methods Primers. - 2662-8449. ; 3:1
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Forskningsöversikt (refereegranskat)abstract
- Two-dimensional electronic spectroscopy (2DES) is a popular technique that can track ultrafast coherent and incoherent processes in real time. Since its development in the late 1990s, 2DES has become a powerful tool for investigating ultrafast dynamics in a range of systems, including nanomaterials and optoelectronic devices. This Primer explains the underlying physical principles of 2DES and how it can be applied to study dynamic photophysical processes. The article discusses how to collect, process and analyse data, with a summary of currently available experimental configurations. Common issues and challenges are considered, focusing on the limitations and reproducibility of the technique, finishing with an exploration of potential future advances and applications.
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| 3. |
- Ghosh, Supriya, et al.
(författare)
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Slower Auger Recombination in 12-Faceted Dodecahedron CsPbBr3 Nanocrystals
- 2023
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 14:4, s. 1066-1072
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Tidskriftsartikel (refereegranskat)abstract
- Over the past two decades, intensive research efforts have been devoted to suppressions of Auger recombination in metal-chalcogenide and perovskite nanocrystals (PNCs) for the application of photovoltaics and light emitting devices (LEDs). Here, we have explored dodecahedron cesium lead bromide perovskite nanocrystals (DNCs), which show slower Auger recombination time compared to hexahedron nanocrystals (HNCs). We investigate many-body interactions that are manifested under high excitation flux density in both NCs using ultrafast spectroscopic pump-probe measurements. We demonstrate that the Auger recombination rate due to multiexciton recombinations are lower in DNCs than in HNCs. At low and intermediate excitation density, the majority of carriers recombine through biexcitonic recombination. However, at high excitation density (>1018 cm-3) a higher number of many-body Auger process dominates over biexcitonic recombination. Compared to HNCs, high PLQY and slower Auger recombinations in DNCs are likely to be significant for the fabrication of highly efficient perovskite-based photonics and LEDs.
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| 4. |
- Hedse, Albin, et al.
(författare)
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Pulse overlap artifacts and double quantum coherence spectroscopy
- 2023
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 158:14
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Tidskriftsartikel (refereegranskat)abstract
- The double quantum coherence (DQC) signal in nonlinear spectroscopy gives information about the many-body correlation effects not easily available by other methods. The signal is short-lived, consequently, a significant part of it is generated during the pulse overlap. Since the signal is at two times the laser frequency, one may intuitively expect that the pulse overlap-related artifacts are filtered out by the Fourier transform. Here, we show that this is not the case. We perform explicit calculations of phase-modulated two-pulse experiments of a two-level system where the DQC is impossible. Still, we obtain a significant signal at the modulation frequency, which corresponds to the DQC, while the Fourier transform over the pulse delay shows a double frequency. We repeat the calculations with a three-level system where the true DQC signal occurs. We conclude that with realistic dephasing times, the pulse-overlap artifact can be significantly stronger than the DQC signal. Our results call for great care when analyzing such experiments. As a rule of thumb, we recommend that only delays larger than 1.5 times the pulse length should be used.
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| 5. |
- Li, Guohui, et al.
(författare)
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Localized Bound Multiexcitons in Engineered Quasi-2D Perovskites Grains at Room Temperature for Efficient Lasers
- 2023
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 35:20
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Tidskriftsartikel (refereegranskat)abstract
- Reducing the excitation threshold to minimize the Joule heating is critical for the realization of perovskite laser diodes. Although bound excitons are promising for low threshold laser, how to generate them at room temperature for laser applications is still unclear in quasi-2D perovskite-based devices. In this work, via engineering quasi-2D perovskite PEA2(CH3NH3)n-1PbnBr3n+1 microscopic grains by the anti-solvent method, room-temperature multiexciton radiative recombination is successfully demonstrated at a remarkably low pump density of 0.97 µJ cm−2, which is only one-fourth of that required in 2D CdSe nanosheets. In addition, the well-defined translational momentum in quasi-2D perovskite grains can restrict the Auger recombination which is detrimental to radiative emission. Furthermore, the quasi-2D perovskite grains are favorable for increasing binding energies of excitons and biexcitons and so as the related radiative recombination. Consequently, the prepared phase quasi-2D perovskite film renders a threshold of room-temperature stimulated emission as low as 13.7 µJ cm−2, reduced by 58.6% relative to the amorphous counterpart with larger grains. The findings in this work are expected to facilitate the development of solution-processable perovskite multiexcitonic laser diodes.
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| 6. |
- Wang, Xinyue, et al.
(författare)
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Charge-Separated States Determined Photoinduced Electron Transfer Efficiency in a D-D-A System in an External Electric Field
- 2023
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455.
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Tidskriftsartikel (refereegranskat)abstract
- Focusing on the photoinduced electron transfer properties of the D-D-A molecule ((TPA-TT)-BODIPY-C60) in an external electric field (Fext), the excited-state properties in which the double-donor molecule is excited to form three charge-separated states were simulated. The charge-Transfer processes of these three charge-separated states were investigated by considering the two donors as a whole ((TPA-TT-BODIPY)·+-C60·-) as a comparison object. The electronic coupling (VDA), reorganization energy (λ), and free energy (δG) of the different charge-separated states in Fext were calculated and simulated. The calculated results show that the λ of (TPA-TT-BODIPY)·+-C60·- ranges from 0.576 to 0.51 eV, and the calculated δG of exciton dissociation ranges from-1.402 to-1.143 eV, indicating that exciton dissociation occurs in the Marcus inverted region. In the range of Fext =-10 × 10-5 to 10 × 10-5 au, the trend of the charge-Transfer rate is gradually increasing, and the rate increase is mainly from the VDA and δG changes. Moreover, the rapid formation of the (TPA-TT)-BODIPY·+-C60·- charge-separated state and the formation of the long-lived (TPA-TT)·+-BODIPY-C60·- are indicated by the exciton dissociation rate. By studying the charge-Transfer parameters under different electric field directions, it is found that the regulation of electric field strength on the charge-Transfer rate is consistent. These results provide a feasible method for the rational design of a new type of electron transfer process with high efficiency of the D-D-A system.
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| 7. |
- Wang, Xinyue, et al.
(författare)
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Exploring the effect of electric field on charge-transfer states at non-fullerene D/A interface
- 2023
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Ingår i: Journal of Molecular Liquids. - 0167-7322. ; 390
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Tidskriftsartikel (refereegranskat)abstract
- Using Marcus theory, the electric-field-dependent charge-separation dynamics of non-fullerene acceptors D/A heterojunctions are simulated. On the D/A interface, the excited-state characteristics show obvious differences under different electric field intensities, providing microscopic details of the non-fullerene D/A interface at the atomic level. For different electric field conditions, so the calculated reorganization energy ranges from 0.97 to 1 eV. By comparing other charge transfer parameters of this system, it was found that the reorganization energy mainly determines the charge-transfer rate. The results show that the charge transfer rate does exhibit a variation that depends on the electric field intensity and is consistent with the variation in the Marcus inverted region. By evaluating the rate of charge separation/recombination, it is judged that its charge separation shows significant advantages, and the trifurcated structure of the molecule also provides multiple charge transfer paths for charge separation, which contributes to the charge generation mechanism.
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| 8. |
- Wang, Xinyue, et al.
(författare)
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External electric field-dependent photoinduced charge transfer in non-fullerene organic solar cells
- 2023
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Ingår i: Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425. ; 284
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Tidskriftsartikel (refereegranskat)abstract
- Based on Marcus theory, the photoinduced electron transfer properties of D-A type non-fullerene acceptor organic solar cells (OSCs) under the dependence of external electric field (Fext) were investigated. The research results shown that the charge transfer mode under different Fext intensities changes with certain regularity. Focusing on the important parameters (ΔG, λ, and VDA) that affect the charge transfer rate, it was found that both charge separation (|ΔGCS|>λ(1.3019 vs 0.8275 eV at Fext = 0) and charge recombiation (|ΔGCR|>λ, (1.9633 vs 0.8275 eV)) processes occur in the Marcus inverted region. The ΔGCS is relatively sensitive to Fext, and the calculated ΔGCS at different Fext intensities yields an increment of 0.0073 eV, which is also the main reason for the increase in the rate of charge separation. The ΔGCR ranges between −1.9633 and −1.9637 eV, is insensitive to Fext, and ΔGCR is significantly smaller than ΔGCS, which makes the charge recombination rate significantly smaller than the charge separation rate. For VDA, it is found that VDA will transition to a new level only when the Fext intensity reaches a certain intensity, which also enables to obtain a faster charge separation rate. By studying the charge transfer parameters in different polar solvents, it is found that polar solvents can indeed increase the charge transfer rate. To a certain extent, our results also demonstrate that the addition of Fext can further improve the performance of non-fullerene acceptor OSCs.
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