Exciton diffusion in organic semiconductors

Mikhnenko, Oleksandr V.; Blom, Paul W. M.; Nguyen, Thuc‐Quyen

doi:10.1039/c5ee00925a

Cited by 723 publications

(832 citation statements)

References 282 publications

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“…64,65 The initial nuclear positions, () (0) derived from exciton-exciton annihilation measurements 70 although larger than other 26 exciton diffusion coefficients of Pc-based amorphous materials. 71 However, the diffusion coefficient of the ZnPc aggregate was estimated by assuming an incoherent regime with an exciton transfer rate of ~1.0 × 10 13 s −1 , which is close to the limit of validity of a first order rate process in a molecular system. The agreement between the theoretical and experimental exciton diffusion coefficients suggests that the model proposed here is able to correctly describe exciton diffusion, but without assuming an incoherent regime, which would be incompatible with the J and λ parameters of this system (see Section 3).…”

Section: Exciton Dynamicsmentioning

confidence: 99%

Exciton Dynamics in Phthalocyanine Molecular Crystals

2016

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In this paper, the exciton transport properties of an octa(butyl)-substituted metal-free phthalocyanine (H2-OBPc) molecular crystal have been explored by means of a combined computational (molecular dynamics and electronic structure calculations) and theoretical (model Hamiltonian) approximation. The excitonic couplings in phthalocyanines, where multiple quasi-degenerate excited states are present in the isolated chromophore, are computed with a multistate diabatization scheme which is able to capture both short-and long-range excitonic coupling effects. Thermal motions in phthalocyanine molecular crystals at room temperature cause substantial fluctuation of the excitonic couplings between neighboring molecules (dynamic disorder). The average values of the excitonic couplings are found to be not much smaller than the reorganization energy for the excitation energy transfer and the commonly assumed incoherent regime for this class of materials cannot be invoked. A simple but realistic model Hamiltonian is proposed to study the exciton dynamics in phthalocyanine molecular crystals or aggregates beyond the incoherent regime.2

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Section: Exciton Dynamicsmentioning

confidence: 99%

Exciton Dynamics in Phthalocyanine Molecular Crystals

2016

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“…where dL i is the Euclidean distance between the generation and final site of exciton i and N s/t denotes the number of either singlet or triplet excitons [82]. The presented results show the average effective diffusion lengths of eight configurations simulated for each dopant concentration, while the error bars indicate the standard deviation.…”

Section: Impact Of Dopant Volume Concentration On Exciton Dynamicsmentioning

confidence: 99%

“…We will now describe all physical rates modeled for both singlets and triplets, as well as the conversion rates between these excitons. For a detailed discussion on the photophysical processes, please refer to [64,82]. A schematic overview of the rates and the corresponding energetic levels are depicted in Figure 5.…”

Section: Excitonsmentioning

confidence: 99%

Generalized Kinetic Monte Carlo Framework for Organic Electronics

et al. 2018

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Abstract:In this paper, we present our generalized kinetic Monte Carlo (kMC) framework for the simulation of organic semiconductors and electronic devices such as solar cells (OSCs) and light-emitting diodes (OLEDs). Our model generalizes the geometrical representation of the multifaceted properties of the organic material by the use of a non-cubic, generalized Voronoi tessellation and a model that connects sites to polymer chains. Herewith, we obtain a realistic model for both amorphous and crystalline domains of small molecules and polymers. Furthermore, we generalize the excitonic processes and include triplet exciton dynamics, which allows an enhanced investigation of OSCs and OLEDs. We outline the developed methods of our generalized kMC framework and give two exemplary studies of electrical and optical properties inside an organic semiconductor.

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“…Notice that considering that each film requires 60 µL of solution with a typical solid content of 20 mg mL −1 , only 1.2 mg of material is needed per film, and a single film already contains most of the required information regarding thickness effects of a specific blend. Interestingly, this method can be used for other applications beyond OPV optimization, including the study of the geometrical confinement on phase transition temperatures, [32] determination of exciton diffusion lengths, [33] fabrication of position sensitive photodetectors, [34] or as miniature spectrophotometers based on microcavity resonators with a wedged active layer. [35] We extend here this method beyond thickness gradients to also include the preparation of films with D:A composition gradients.…”

Section: Casting Methodsologymentioning

confidence: 99%

High‐Throughput Multiparametric Screening of Solution Processed Bulk Heterojunction Solar Cells

Sánchez-Díaz

Rodríguez‐Martínez

Córcoles-Guija

et al. 2018

Adv Elect Materials

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(MDMO-PPV) or poly(3-hexylthiophene) (P3HT) combined with soluble fullerenes, [6,7] up to current PCE values exceeding 10% for several systems. [9][10][11][12][13] There is no specific fundamental limitation to organic materials that indicates that much higher values are not possible, and the number of potential candidates is nearly infinite. Indeed, the organic nature of the photoactive materials offers a myriad of possibilities to modify their chemical structure; for the case of conjugated polymers, there exists a vast assortment of combinations depending on the choice of moieties, the bridging atoms, the length and branching points of the alkyl side chains, and the molecular weight, to name but a few. Using search engines to inspect the literature, we estimate that in the last ten years ≈5000 organic conjugated materials have been tested in BHJ solar cells, albeit only a few tenths have been studied and optimized in depth. While applied quantum theory can help to select promising candidates, [14][15][16] the final performance often depends on a number of issues difficult to predict a priori, such as solubility, miscibility of compounds, tendency to crystallize, exact energy levels in the blend, etc. In practice, this means that for a given promising backbone, a family of systems need to be tested, including different side chains, molecular weights, donor:acceptor combinations, etc. [17] Within this large and uncharted spectrum of materials and processing variables, combinatorial screening methodologies are highly on demand to speed up their exploration while helping the technology to approach the theoretical Shockley-Queisser limit of >20% PCE. [18,19] From the engineering point of view, three main aspects must be addressed for the evaluation of a material system for BHJ solar cells, namely the active layer thickness, the donor-acceptor (D:A) blending ratio and the nanoscale morphology (typically controlled by deposition conditions, thermal annealing, and use of additives). Ideally, those three variables can be optimized separately and to some extent it is usually an acceptable approximation; however, the full potential of a novel active layer material requires for fine tuning of the preparation conditions that take into consideration the subtle interplay between them. [20] For instance, the optimum thickness is often found close to the first interference maximum, which is governed by the refractive index of the active layer; this, on the other hand, will be a function of the D:A ratio (fullerenes typically have higher refractive index than polymers) and the degree of crystallinity One of the major bottlenecks in the development of organic photovoltaics is the time needed to evaluate each material system. This time ranges from weeks to months if different variables such as blend composition, thickness, annealing, and additives are to be explored. In this study, the use of lateral gradients is proposed in order to evaluate the photovoltaic potential of a material system up to 50 times faster. A platform that c...

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Exciton diffusion in organic semiconductors

Abstract: Experiments and basic Physics of exciton diffusion in organic semiconductors are reviewed.

Cited by 723 publications

References 282 publications

Exciton Dynamics in Phthalocyanine Molecular Crystals

Exciton Dynamics in Phthalocyanine Molecular Crystals

Generalized Kinetic Monte Carlo Framework for Organic Electronics

High‐Throughput Multiparametric Screening of Solution Processed Bulk Heterojunction Solar Cells

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