Theoretical study of the effects of different substituents of tetrathiafulvalene derivatives on charge transport

Li, Huixue; Li, Zhifeng

doi:10.1007/s11434-012-5222-z

Cited by 11 publications

(3 citation statements)

References 45 publications

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“…One suggested way to indirectly incorporate the effects of molecular packing, and thus to get a better estimate of λ int within a crystal, is to constraint the all atoms of neutral TTF molecules to move only in a single plane . This constraint has since been adopted by other works using both approaches (i) and (ii) to calculate λ int . Calculation of λ int using approach (ii) can also be performed using only experimental molecular vibrational data provided from Raman spectra.…”

Section: Theoretical Modelling Of Charge Transport In Ttf Derivativesmentioning

confidence: 99%

Tuning Crystal Ordering, Electronic Structure, and Morphology in Organic Semiconductors: Tetrathiafulvalenes as a Model Case

Pfattner

Bromley

Rovira

et al. 2015

Adv Funct Materials

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Tetrathiafulvalenes (TTFs) are an appealing class of organic small molecules giving rise to some of the highest performing active materials reported for organic field effect transistors (OFETs). Because they can be easily chemically modified, TTF‐derivatives are ideal candidates to perform molecule–property correlation studies and, especially, to elucidate the impact of molecular and crystal engineering on device performance. A brief introduction into the state‐of‐the‐art of the field‐effect mobility values achieved with TTF derivatives employing different fabrication techniques is provided. Following, structure–performance relationships are discussed, including polymorphism, a phenomenon which is crucial to control for ensuring device reproducibility. It is also shown that chemical modification of TTFs has a strong influence on the electronic structure of these materials, affecting their stability as well as the nature of the generated charge carriers, leading to devices with p‐channel, n‐channel, or even ambipolar behaviour. TTFs have also shown promise in other applications, such as phototransistors, sensors, or as dopants or components of organic metal charge transfer salts used as source–drain contacts. Overall, TTFs are appealing building blocks in organic electronics, not only because they can be tailored to perform fundamental studies, but also because they offer a wide spectrum of potential applications.

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Section: Theoretical Modelling Of Charge Transport In Ttf Derivativesmentioning

confidence: 99%

Tuning Crystal Ordering, Electronic Structure, and Morphology in Organic Semiconductors: Tetrathiafulvalenes as a Model Case

Pfattner

Bromley

Rovira

et al. 2015

Adv Funct Materials

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“…Here m is the dimensionality of the space and l is a specific transfer pathway, r l is distance between two site within l and k l is the corresponding transfer rate that can be calculated from Eq. (2.14), and P l is the relative probability of charge transfer within l which can be calculated from P l = k l / l k l [59,60].…”

Section: Charge Collectionmentioning

confidence: 99%

Excitation Dynamics and Losses in Solution Processed Disordered Semiconductors

Zarrabi¹

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From a technological point of view, organic semiconductor-based devices are of significant interest due to their light weight, ease of processability, conformal flexibility and potentially low cost and low embodied energy pro-duction. Motivated by these quite unique selling points, the performance of organic semiconductors has been a subject of multi-disciplinary study for more than 60 years with steady progress in applications such as solar cells, transistors, light emitting diodes and various sensors. One of the main characteristics that governs the performance of organic semiconduc-tors is their low dielectric constants, meaning they are excitonic at room temperature. A second main feature that dictates the charge carrier recom-bination and transport properties is the disordered nature of these semicon-ductors causing low charge carrier mobilities. The work described in this thesis focuses on these defining elements, and particularly their implications on photovoltaic devices. The discussion will start with a review into the main electro-optical phenomena in organic solar cells. Subsequently, a new method is presented for measuring exciton diffusion lengths based upon a low-quencher-content device structure. An anomalously large quenching volume is observed that can be assigned to long-range exciton delocaliza-tion prior to thermalization. These ultra-low-impurity content organic so-lar cells are also very useful as model systems to study and engineer trap states. Using this approach, it is found that mid-gap trap states are a universal feature in organic semiconductor donor-acceptor blends and un-expectedly contribute to charge generation and recombination. This has a profound impact on the thermodynamic limit of organic photovoltaic de-vices. Having demonstrated this important new insight it is further shown that a definitive link exists between a reduced recombination rate compared to the Langevin rate in some exceptional, high performance material sys-tems and a significant increase in the dissociation rate of charge transfer states upon post-processing of the active layer. In sum, the work presented in this thesis delivers important new insight as to the underlying dynamics of exciton generation and diffusion, charge transfer state dissociation, and indeed the ultimate fate of photogenerated free carriers.

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“…where z is the total number of available sites, P l = k l /Σ i k i , while k l is the rate along path l and Σ i k i is the total hopping rate away from the site [116,117].…”

Section: Carrier Transportmentioning

confidence: 99%

On the Relation Between Exciton Dynamics and Nano-Morphology in Organic Semiconductor Blends

Riley¹

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Optoelectronic processes in semiconductor-based devices are widely understood through the constructs of highly-symmetric crystalline inorganic systems, where the lattice periodicity allows significant simplification. Emerging technologies, such as organic semiconductor-based devices, share many qualities with crys-talline inorganic semiconductors; however, they diverge in subtle yet important ways. Optical absorption in organic semiconductors gives rise to long-lived and tightly-bound excitons, which migrate in manner often disregarded in the un-derstanding of highly-symmetric crystalline inorganic semiconductors. Further, ‘free’ charge carriers in organic semiconductors ‘hop’ between organic molecules in a disordered film rather than the undergo band transport that delocalised car-riers in periodic lattices do. This hopping transport leads to lower charge carrier mobilities which have far-reaching ramifications to device operation.In the work summarised in this thesis the effect that excitonic and charge transport have on device performance of solar cells based on organic photo-voltaics will be explored. Experimental techniques are designed and developed to gain insight into the efficiency of exciton transport, the nanostructure of organic-semiconductor blends, and the relation between charge injection and extraction. Utilising these techniques, various state-of-the art systems are examined in detail and various pathways for improving device performance are voiced.Specifically, a technique to measure the exciton diffusion length in organic semiconductors is developed and shown to have many advantages over established techniques while improving the accuracy of the measurement. This technique is expanded to blends of organic semiconductors to quantify the efficiency of dif-fusion and quenching occurring between semiconductors in blends. This, along with a developed theoretical understanding, allows for the size of the phase sepa-rated domains to be quantified. Relationships between the excitons generated in organic semiconductors, charge carriers created in the blends, and the transport of charges to and extraction at the electrodes is considered in detail. Finally, a technique to distinguish between the nonradiative recombination occurring within an organic semiconductor blend and at the interface between the blend and the larger device structure is introduced. This technique utilises the well-establish reciprocity theory to reconcile the imbalance between charge injection and ex-traction unique to low-mobility organic semiconductors.

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Theoretical study of the effects of different substituents of tetrathiafulvalene derivatives on charge transport

Cited by 11 publications

References 45 publications

Tuning Crystal Ordering, Electronic Structure, and Morphology in Organic Semiconductors: Tetrathiafulvalenes as a Model Case

Tuning Crystal Ordering, Electronic Structure, and Morphology in Organic Semiconductors: Tetrathiafulvalenes as a Model Case

Excitation Dynamics and Losses in Solution Processed Disordered Semiconductors

On the Relation Between Exciton Dynamics and Nano-Morphology in Organic Semiconductor Blends

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