Topic
Exciton
About: Exciton is a research topic. Over the lifetime, 31603 publications have been published within this topic receiving 810642 citations.
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TL;DR: It is demonstrated, through a combination of optical spectroscopy and multiscale modeling as a function of the degree of polycrystallinity and temperature, that the electron-hole interaction is sensitive to the microstructure of the material.
Abstract: Solar cells based on hybrid inorganic-organic halide perovskites have demonstrated high power conversion efficiencies in a range of architectures. The existence and stability of bound electron-hole pairs in these materials, and their role in the exceptional performance of optoelectronic devices, remains a controversial issue. Here we demonstrate, through a combination of optical spectroscopy and multiscale modeling as a function of the degree of polycrystallinity and temperature, that the electron-hole interaction is sensitive to the microstructure of the material. The long-range order is disrupted by polycrystalline disorder and the variations in electrostatic potential found for smaller crystals suppress exciton formation, while larger crystals of the same composition demonstrate an unambiguous excitonic state. We conclude that fabrication procedures and morphology strongly influence perovskite behaviour, with both free carrier and excitonic regimes possible, with strong implications for optoelectronic devices.
236 citations
TL;DR: It is demonstrated that the MEG efficiency in PbSe does not decrease when the QDs are treated with hydrazine, which has been shown to greatly enhance carrier transport in P bSe QD films by decreasing the interdot distance.
Abstract: We study multiple exciton generation (MEG) in electronically coupled films of PbSe quantum dots (QDs) employing ultrafast time-resolved transient absorption spectroscopy. We demonstrate that the MEG efficiency in PbSe does not decrease when the QDs are treated with hydrazine, which has been shown to greatly enhance carrier transport in PbSe QD films by decreasing the interdot distance. The quantum yield is measured and compared to previously reported values for electronically isolated QDs suspended in organic solvents at ∼4 and 4.5 times the effective band gap. A slightly modified analysis is applied to extract the MEG efficiency and the absorption cross section of each sample at the pump wavelength. We compare the absorption cross sections of our samples to that of bulk PbSe. We find that both the biexciton lifetime and the absorption cross section increase in films relative to isolated QDs in solution.
236 citations
TL;DR: The spectral shape, temperature dependence, and radiative lifetime are consistent with a short-lived superradiant exciton delocalized over approximately 10 tetracene molecules.
Abstract: The structure and dynamics of luminescent excitons in tetracene thin films and nanoaggregates are investigated using time-resolved spectroscopy and theoretical calculations. The orientation of tetracene's transition dipole moment along its short molecular axis leads to properties qualitatively different from those observed in aggregates of phenylene-vinylene and thiophene oligomers, despite similar crystal structures. The spectral shape, temperature dependence, and radiative lifetime are consistent with a short-lived superradiant exciton delocalized over approximately 10 tetracene molecules.
235 citations
TL;DR: A theory for polarized absorption in crystalline oligoacenes is presented, which includes Frenkel exciton coupling, the coupling between Frenkel and charge-transfer (CT) excitons, and the coupling of all neutral and ionic excited states to the dominant ring-breathing vibrational mode.
Abstract: A theory for polarized absorption in crystalline oligoacenes is presented, which includes Frenkel exciton coupling, the coupling between Frenkel and charge-transfer (CT) excitons, and the coupling of all neutral and ionic excited states to the dominant ring-breathing vibrational mode. For tetracene, spectra calculated using all Frenkel couplings among the five lowest energy molecular singlet states predict a Davydov splitting (DS) of the lowest energy (0–0) vibronic band of only −32 cm−1, far smaller than the measured value of 631 cm−1 and of the wrong sign—a negative sign indicating that the polarizations of the lower and upper Davydov components are reversed from experiment. Inclusion of Frenkel-CT coupling dramatically improves the agreement with experiment, yielding a 0–0 DS of 601 cm−1 and a nearly quantitative reproduction of the relative spectral intensities of the 0–n vibronic components. Our analysis also shows that CT mixing increases with the size of the oligoacenes. We discuss the implications...
235 citations
TL;DR: In this article, multiexciton dynamics in monolayer WSe2 using nonlinear photoluminescence (PL) spectroscopy and Monte Carlo simulations were studied and demonstrated that the diffusion-assisted exciton-exciton annihilation (EEA) model accounts for the observed nonlinear PL behavior.
Abstract: We studied multiexciton dynamics in monolayer WSe2 using nonlinear photoluminescence (PL) spectroscopy and Monte Carlo simulations. We observed strong nonlinear saturation behavior of exciton PL with increasing excitation power density and long-distance exciton diffusion, reaching several micrometers. We demonstrated that the diffusion-assisted exciton-exciton annihilation (EEA) model accounts for the observed nonlinear PL behavior. The long-distance exciton diffusion and subsequent efficient EEA process determined the unusual multiexciton dynamics in atomically thin layered transition metal dichalcogenides.
234 citations