6 research outputs found
Recommended from our members
On exciton-vibration and exciton-photon interactions in organic semiconductors
Organic semiconductors are materials that are promising for novel optoelectronic applications, such as more efficient solar cells and LEDs. The optoelectronic response of these materials is dominated by bound electron-hole pairs called excitons, which are often strongly affected by hundreds of possible molecular vibrations. Although quantum theory contains all the ingredients to describe these complex phenomena, in practice it is only possible to solve the corresponding equations in small systems with few vibrations. As a result, it has been common to assume weak exciton-vibration interactions and to employ perturbative approaches. Similarly, exciton-photon interactions have almost universally been treated in the so-called weak coupling regime. However, in recent years it has become increasingly clear that these approximations can break down in organic semiconductors, placing an important roadblock towards the novel energy-harvesting technologies that could be based on these materials.
In this thesis we address this issue by developing methods to treat exciton-photon and exciton-vibration interactions, without relying on any approximation regarding their magnitude. We propose a first principles description of hybrid exciton-light (polariton) states that result from strong exciton-photon interactions. We discuss a method to treat strong exciton-vibration interactions, showing that the spatial extent of exciton states controls their magnitude. Subsequently, we present a beyond Born-Oppenheimer method based on tensor networks to study real-time exciton dynamics. By using these methods, we show how selective excitation of vibrational modes can enhance charge transfer. Moreover, through rigorous comparison to experiments, we highlight that tensor network methods are highly accurate, and we generate a `movie' of the photophysical process of singlet fission, which occurs during early light-harvesting by organic molecules and has the potential to increase solar cell efficiencies. Finally, we construct a singlet fission model including the effects of excess energy, vibrations and the solvent of molecules concurrently, demonstrating that the fission mechanism can be qualitatively changed in a controlled manner, allowing for its acceleration by an order of magnitude.Winton Programme for the Physics of Sustainabilit
Recommended from our members
Data supporting "Non-equilibrium relaxation of hot states in organic semiconductors: Impact of mode-selective excitation on charge transfer"
This data set contains all data necessary to generate the figures that contain computational data in the manuscript. Detailed information on how the data was obtained may be found in the open access manuscript which has been deposited in this repository. Figure 6 - Exciton populations for no excess energy present. Figure 7 - displacement of vibrational modes over the course of the dynamics without excess energy. Figure 8 - Exciton population for the case of adding excess energy to a vibrational mode incoherently. Figure 9 - Exciton population for the case of adding excess energy to a vibrational mode coherently. Figure 10 - Closer view of the early-time dynamics of Figure 9. Figure 11 - Yield of charge transfer vs excess energy, for the cases of exciting a high- vs a low-frequency mode. Figure 12 - Coherence of the quantum dynamics for the cases of no excess energy and excess energy added coherently. Figure 13 - Time-dependent vibrational displacement, indicating vibrational relaxation towards low-frequency modes
Recommended from our members
Research data underlying "Systematic improvement of molecular excited state calculations by inclusion of nuclear quantum motion: a mode-resolved picture and the effect of molecular size"
This dataset contains all the raw data for reproducing the results and figures of the associated publication. See README files for more information
Recommended from our members
Data associated with: Exciton Diffusion in Highly-Ordered One Dimensional Conjugated Polymers: Effects of Back- Bone Torsion, Electronic Symmetry, Phonons and Annihilation
Origin work book containing absorption spectra, transient absorption data, transient absorption microscopy (TAM) data and associated mean-square displacement plots. Fluence dependent data is also included as well as modelling
Recommended from our members
Data Supporting "Switching between coherent and incoherent singlet fission via solvent-induced symmetry-breaking"
This data set contains all data necessary to generate the figures in the manuscript. Detailed information on how the data was obtained may be found in the open access manuscript which has been deposited in this repository. Figure 1 - structure and general photo physics of the DT-Mes molecule. Figure 2 - determination of the energy levels of DT-Mes and multiple emissive species. Figure 3 - Transient absorption spectroscopy and excited state evolution. Figure 4 - Transient absorption spectroscopy and varying TT/CT balance. Figure 5 - TT and CT action spectra. Figure 6 - switching between coherent and incoherent singlet fission Figure 7 - multidimensional plot of the surfaces participating in the last part of singlet fission. Figure 8 - summary of singlet fission mechanism
Recommended from our members
Data Supporting "First principles modeling of exciton-polaritons in polydiacetylene chains"
The compressed directory data.tar.gz contains different folders that correspond to the various Figures of the article "First principles modeling of exciton-polaritons in polydiacetylene chains" (apart from Figures 1,2,4,6,9 which are schematics). These folders contain plan text .dat files with all the data necessary to reproduce the figures. The x-axis values are given in the first column of the .dat files, while the y-axis values are generally given in the 2nd column. Each figure subdirectory contains a README file with more information on the units of the physical quantities, and a more detailed description.
Briefly, the figure contents are as follows:
Figure 3: Experimental reflectivity and absorption spectra of the two variants of polydiacetylene crystals.
Figure 5: Theoretical estimate of the imaginary part of the dielectric response of two real and two model PDA systems, obtained from GW-BSE calculations.
Figure 7: (a) Polariton dispersion of the model blue PDA system, as obtained from our presented methodology. (b) The associated reflectance of this systems.
Figure 8: Group velocity of the lower polariton band of the model blue PDA system, for different incident photon energies.
Figure 10: Dependence of the exciton energy and the stop-band width on the number of diacetylene monomers of a polymer chain.
Figure 11: The effect of vibrations on the (a) imaginary and (b) real parts of the dielectric response of the model blue PDA system. The associated reflectance is given in Figure (c).
Figure 12: Dependence of Delta_vib on the exciton coherence length for the two model PDA systems.
Figure 13: Dependence of Delta_vib on the width gamma of the exciton and vibronic peaks in the absorption spectrum