Directional energy transfer in columnar liquid crystals: A computer-simulation study

Bacchiocchi, Corrado; Zannoni, Claudio

doi:10.1103/physreve.58.3237

Cited by 18 publications

(22 citation statements)

References 36 publications

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“…Other quantum chemical-methods such as the transition density cube method [48] and the distributed monopole approximation [49] calculate the Coulombic coupling between transition states more realistically, but are computationally intensive [46,50]. Energy transfer is usually much faster than intramolecular vibrational relaxation, which means that the donor and acceptor sites are “frozen” while energy transfer occurs [51]. However, there are some exceptions [52,53] in which case a generalised version of Förster theory is more appropriate [54].…”

Section: Exciton Transportmentioning

confidence: 99%

“…As a result, thermally sublimed structurally ordered materials often exhibit larger diffusion lengths than less ordered spin-cast polymers [19,66,67]. Structural order not only affects the spatially averaged diffusion length, but may also affect the preferred direction of exciton hops as indicated by Monte Carlo simulations [51,59,68]. Hence, molecular ordering could be used to direct excitons to the heterointerface where efficient exciton dissociation occurs.…”

Section: Exciton Transportmentioning

confidence: 99%

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Organic Solar Cells: Understanding the Role of Förster Resonance Energy Transfer

Feron

Belcher

Fell

et al. 2012

IJMS

111

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Organic solar cells have the potential to become a low-cost sustainable energy source. Understanding the photoconversion mechanism is key to the design of efficient organic solar cells. In this review, we discuss the processes involved in the photo-electron conversion mechanism, which may be subdivided into exciton harvesting, exciton transport, exciton dissociation, charge transport and extraction stages. In particular, we focus on the role of energy transfer as described by Förster resonance energy transfer (FRET) theory in the photoconversion mechanism. FRET plays a major role in exciton transport, harvesting and dissociation. The spectral absorption range of organic solar cells may be extended using sensitizers that efficiently transfer absorbed energy to the photoactive materials. The limitations of Förster theory to accurately calculate energy transfer rates are discussed. Energy transfer is the first step of an efficient two-step exciton dissociation process and may also be used to preferentially transport excitons to the heterointerface, where efficient exciton dissociation may occur. However, FRET also competes with charge transfer at the heterointerface turning it in a potential loss mechanism. An energy cascade comprising both energy transfer and charge transfer may aid in separating charges and is briefly discussed. Considering the extent to which the photo-electron conversion efficiency is governed by energy transfer, optimisation of this process offers the prospect of improved organic photovoltaic performance and thus aids in realising the potential of organic solar cells.

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Section: Exciton Transportmentioning

confidence: 99%

Section: Exciton Transportmentioning

confidence: 99%

Organic Solar Cells: Understanding the Role of Förster Resonance Energy Transfer

Feron

Belcher

Fell

et al. 2012

IJMS

111

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“…In addition, in a homeotropic nematic layer k ET in the direction perpendicular to the interface is considerably higher than k ET in other directions, as discussed in the literature. [40,41] The efficient exciton transfer in the direction perpendicular to the TnBuPP/TiO 2 interface makes these bilayers promising candidates for photovoltaic applications. This study shows that an efficient light-harvesting layer is realized by a homeotropic nematic molecular arrangement.…”

mentioning

confidence: 99%

Efficient Light‐Harvesting Layers of Homeotropically Aligned Porphyrin Derivatives

et al. 2006

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The dye-sensitized solar cell, based on a wide-bandgap semiconductor photosensitized with an organic dye, is an attractive low-cost alternative to conventional silicon-based solar cells.[1] Absorption of a photon by the dye results in the formation of a strongly bound electron-hole pair, also referred to as an exciton. A key feature of the dye-sensitized solar cell is that efficient exciton decay into separate charge carriers can only occur at the interface between the dye and the semiconductor, leading to injection of an electron into the conduction band of the semiconductor. [2] Since O'Regan and Grätzel reported an efficiency over 10 % for a cell based on an interpenetrating network of dye-coated nanocrystalline TiO 2 particles and a liquid electrolyte containing a iodide/ triiodide redox mediator, [3] the use of nanostructured films in photovoltaic devices has been studied extensively. Due to complications involved in the use of a liquid electrolyte, [4] there is presently great interest in the development of all-solid-state organic/inorganic solar cells. For these cells a maximum performance of 4 % has been realized so far.[5] The use of nanostructured networks avoids the necessity of long-range exciton diffusion through the dye layer. However, in such systems electron transport is hampered by trapping at surface defects.[6] The difficulties involved in electron transport can be avoided by using a bilayer configuration consisting of a bulk semiconductor and a relatively thick dye layer. In order to realize efficient charge separation in such a bilayer configuration, the distance excitons are able to cover by diffusion (exciton diffusion length) needs to be equal to or larger than the light penetration depth, which has a typical value of 50-100 nm. The exciton diffusion length in molecular organic dye layers is usually of the order of only a few nanometers, [7][8][9][10] although Nature shows that it is possible to transport excitation energy efficiently over considerably longer distances. An example is found in the photosynthetic apparatus of purple bacteria, which consists of reaction centers and two types of lightharvesting complexes: LHI and LHII. The light-harvesting complexes consist of chlorophyll and carotenoid molecules, kept in place by proteins. [11][12][13] The presence of chlorophyll molecules leads to a strong light absorption. In addition, the structure of the light-harvesting complexes provides a highly efficient pathway for exciton transport; 80-90 % of the excitons formed on light absorption are transferred to the reaction center, where charge separation occurs.[14] For a few molecular dye systems only, exciton diffusion lengths considerably longer than a few nanometers have been realized in vacuum thermal deposited layers. [15,16] However, the expensive elaborate deposition technique makes these layers commercially less attractive and could only be applied for a few dye materials. Chlorophylls and their analogues are attractive candidates for application in dye-sensitized solar cells, [17,1...

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“…This is due to the high degree of carbon-carbon doublebonding within the central structure of four benzene rings leading to highly delocalised electron density acrossthe molecule [8]. Hexaoctylthiotriphenylene(HOTT) (see Figure 1) exhibits semiconducting properties and a structural phase change between a hexagonally packed columnar phase and an isotropic phase [9,10]. By self-consistently modelling the charge transportpropertiesof the two phases we will demonstrate our multi-scale methodology and distinguish distinct electronic regimes that a lattice model could not.…”

Section: Introductionmentioning

confidence: 99%

On the importance of detailed structure in molecular electronics (and why microscopic models cannot see the wood for trees)

et al. 2018

Self Cite

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We study the charge transport properties of a system of liquid crystal discotic molecules in two distinct phases.To differentiate between the two phases, we use a self-consistent model that describes the pairwise interaction between molecules, the electronic coupling between them and the difference in orbital energies.This multi-scale approach hinges upon having systems that are both accurate (to within atomic resolution) and large (,10,000 molecules). The two phases have dramatically different charge transport network topologies, directly correlated to their molecular structures.We quantify the charge transport on both a macroscopic and microscopic scale, taking advantage of the model's resolution to understand the role of molecular packing in charge transport.

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Directional energy transfer in columnar liquid crystals: A computer-simulation study

Cited by 18 publications

References 36 publications

Organic Solar Cells: Understanding the Role of Förster Resonance Energy Transfer

Organic Solar Cells: Understanding the Role of Förster Resonance Energy Transfer

Efficient Light‐Harvesting Layers of Homeotropically Aligned Porphyrin Derivatives

On the importance of detailed structure in molecular electronics (and why microscopic models cannot see the wood for trees)

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