Higher-Energy Charge Transfer States Facilitate Charge Separation in Donor–Acceptor Molecular Dyads

Lee, Dong-Hyun; Forsuelo, Michael A.; Kocherzhenko, Aleksey A.; Whaley, K. Birgitta

doi:10.1021/acs.jpcc.7b03197

Cited by 15 publications

(16 citation statements)

References 43 publications

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“…However, in some cases intermolecular charge transfer states may significantly affect the optoelectronic properties of molecular materials 46 . In principle, such charge transfer can be incorporated into exciton models 27,28 , albeit at a considerably increased computational cost compared to the case when only Frenkel excitons are accounted for.…”

Section: Discussionmentioning

confidence: 99%

“…, where the electron and the hole are localized on the same molecule. Charge transfer excitons, where the electron and the hole are localized on different molecules, may need to be included in some cases (e.g., when modeling charge separation in donor-acceptor systems) 27,28 . Although exciton models are multiscale models that can be parametrized using only first-principle calculations on individual molecules, they still account for intermolecular interactions.…”

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confidence: 99%

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Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids

Kocherzhenko

Shedge

Germaux

et al. 2020

JoVE

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Rational design of disordered molecular aggregates and solids for optoelectronic applications relies on our ability to predict the properties of such materials using theoretical and computational methods. However, large molecular systems where disorder is too significant to be considered in the perturbative limit cannot be described using either first principles quantum chemistry or band theory. Multiscale modeling is a promising approach to understanding and optimizing the optoelectronic properties of such systems. It uses first-principles quantum chemical methods to calculate the properties of individual molecules, then constructs model Hamiltonians of molecular aggregates or bulk materials based on these calculations. In this paper, we present a protocol for constructing a tight-binding Hamiltonian that represents the excited states of a molecular material in the basis of Frenckel excitons: electron-hole pairs that are localized on individual molecules that make up the material. The Hamiltonian parametrization proposed here accounts for excitonic couplings between molecules, as well as for electrostatic polarization of the electron density on a molecule by the charge distribution on surrounding molecules. Such model Hamiltonians can be used to calculate optical absorption spectra and other optoelectronic properties of molecular aggregates and solids. Video Link The video component of this article can be found at https://www.jove.com/video/60598/ 13,14 and time-dependent density functional theory (TD-DFT) 15,16. Organic molecules with applications in optoelectronics typically have relatively large π-conjugated systems; many also have donor and acceptor groups. Capturing the correct charge-transfer behavior in such molecules is essential to calculating their optoelectronic properties, but it can only be accomplished using long-range corrected hybrid functionals in TD-DFT 17,18,19,20. Calculations that use such functionals scale super linearly with the size of the system and, at present, they are only practical for modeling the optoelectronic properties of individual organic molecules or small molecular aggregates that can be described using no more thañ 10 4 atomic basis functions. A simulation method that could describe disordered materials that consist of large numbers of chromophores would be very useful for modeling these systems.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids

Kocherzhenko

Shedge

Germaux

et al. 2020

JoVE

Self Cite

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“… 105 Within this method, we calculate the excitonic couplings between all nonequivalent pairs of molecules in van der Waals contact, 106 e.g., molecules such that at least one distance between any two atoms i and j is shorter than 1.2 × ( r i + r j ) with r i and r j being the van der Waals radii from ref. 107 and also those for which the distance between their mass centers is shorter than 10 Å. Diagonalizing the Hamiltonian enables one to compute the oscillator strength f i for each transition from the ground to the i th excited state of the molecular aggregate as, 108 with μ being the transition dipole moment of the isolated molecule, N the total number of molecules, E i the excitation energies of the aggregate, and c i the eigenstate expansion coefficients. We consider supercells of size 20 × 20 × 20 (with periodic boundary conditions applied for the supercells) to compute the electronic absorption spectrum as which is normalized by the total number of molecules in the supercell to yield the absorption per molecule.…”

Section: Methods and Computational Detailsmentioning

confidence: 99%

Bright Frenkel Excitons in Molecular Crystals: A Survey

2021

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We computed the optical properties of a large set of molecular crystals (∼2200 structures) composed of molecules whose lowest excited states are strongly coupled and generate wide excitonic bands. Such bands are classified in terms of their dimensionality (1-, 2-, and 3-dimensional), the position of the optically allowed state in relation with the excitonic density of states, and the presence of Davydov splitting. The survey confirms that one-dimensional aggregates are rare in molecular crystals highlighting the need to go beyond the simple low-dimensional models. Furthermore, this large set of data is used to search for technologically interesting and less common properties. For instance, we considered the largest excitonic bandwidth that is achievable within known molecular crystals and identified materials with strong super-radiant states. Finally, we explored the possibility that strong excitonic coupling can be used to generate emissive states in the near-infrared region in materials formed by molecules with bright visible absorption and we could identify the maximum allowable red shift in this material class. These insights with the associated searchable database provide practical guidelines for designing materials with interesting optical properties.

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“…Therefore, we examine the photovoltaic behavior of the new D-π-A derivatives mixed whith PCBM (see Fig. 1), as a widely used electron-acceptor in solar cell devices [65][66][67][68][69] . We evaluated the power conversion efficiency (P CE) as the most commonly used parameter to compare the performance of many solar cells, as well as some important parameters such as the short-circuit current density (J sc ), the open circuit voltage (V oc ), and the fill factor (F F ).…”

Section: F Photovoltaic Propertiesmentioning

confidence: 99%

Photophysical Properties of BODIPY-derivatives for the Implementation of Organic Solar Cells: A Computational Approach

Madrid-Usuga,

Ortiz,

Reina

2021

Preprint

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Solar cells based on organic compounds are a proven emergent alternative to conventional electrical energy generation. Here, we provide a computational study of power conversion efficiency optimization of BODIPY-derivatives by means of their associated open circuit voltage, short-circuit density, and fill factor. In so doing, we compute for the derivatives' geometrical structures, energy levels of frontier molecular orbitals, absorption spectra, light collection efficiencies, and exciton binding energies, via density functional theory (DFT) and time dependent (TD)-DFT calculations. We fully-characterize four D-π-A (BODIPY) molecular systems of high efficiency and improved Jsc that are well suited for integration into bulk heterojunction (BHJ) organic solar cells as electron-donor materials in the active layer. Our results are two-fold: We found that molecular complexes with an structural isoxazoline ring exhibit a higher power conversion efficiency (PCE), a useful result for improving the BHJ current, and, on the other hand, by considering the molecular systems as electron-acceptor materials, with P3HT as the electron-donor in the active layer, we found a high PCE compound favorability with a pyrrolidine ring in its structure, in contrast to the molecular systems built with an isoxazoline ring. The theoretical characterization of the electronic properties of the BODIPY-derivatives here provided, computed with a combination of ab-initio methods and quantum models, can be readily applied to other sets of molecular complexes in order to hierarchize optimal power conversion efficiency.

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Higher-Energy Charge Transfer States Facilitate Charge Separation in Donor–Acceptor Molecular Dyads

Cited by 15 publications

References 43 publications

Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids

Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids

Bright Frenkel Excitons in Molecular Crystals: A Survey

Photophysical Properties of BODIPY-derivatives for the Implementation of Organic Solar Cells: A Computational Approach

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