CT-excitons and magnetic field effect in polydiacetylene crystals

Frankevich, E. L.; Lymarev, A. A.; Sokolik, I.

doi:10.1016/0301-0104(92)80215-h

Cited by 15 publications

(7 citation statements)

References 11 publications

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“…Interchain CT states have been observed in PDA, but only in crystals with high polymer contents (10 -2 by weight), well above those studied here. 86 Furthermore, the PIA associated with an intramolecular CT state (transitioning from 2 1 A g -) would be expected to be at $0.9 eV. 87,88 At this push energy, however, we observe no 1 [T.T] signatures, bolstering the claim that the push selectively addresses triplet-pair amplitudes in 2 1 A g -.…”

Section: Ure S9supporting

confidence: 48%

Optical Projection and Spatial Separation of Spin-Entangled Triplet Pairs from the S1 (21 Ag–) State of Pi-Conjugated Systems

Pandya

Cheminal

et al. 2020

Chem

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In quantum mechanics, entanglement is a powerful concept with applications in computing, cryptography, and chemical reactions to boost the efficiency of photovoltaic cells. An example of this in organic semiconductors is the coupling of localized triplet excitons into an overall spin-0, -1, or -2 configuration, termed the triplet-pair state. Here, we develop and apply methods to extract triplet pairs from the lowest excited singlet state in long conjugated molecules (polyenes) and understand the mechanism of this process for the aforementioned applications.

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Section: Ure S9supporting

confidence: 48%

Optical Projection and Spatial Separation of Spin-Entangled Triplet Pairs from the S1 (21 Ag–) State of Pi-Conjugated Systems

Pandya

Cheminal

et al. 2020

Chem

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“…Aside from Zeeman splitting, an external magnetic field adds up to the internal magnetic field created by the atomic nuclei, increasing in that way the inter-system crossing via hyperfine interaction. In this case the relevant Hamiltonian is where B is the external magnetic field, a are the hyperfine coupling constants and I are the hyperfine magnetic fields 24 , 29 . Both terms cause each of the spins to precess with a frequency gμ B B in such a way that when it happens in a randomly oriented spin environment such as that of hyperfine coupling, it induces spin flips that lead to transitions from the singlet to the triplet state, and backwards 27 , 30 .…”

Section: Resultsmentioning

confidence: 99%

“…In our approach, both CT dynamics and precession frequency are on the nanosecond time-scale, where singlet and triplet CTs are still energetically apart and the scheme we described above for ISC holds. In such a scenario, the spin states evolution is still permitted and,provided the triplet CT has a longer lifetime than the singlet, a magnetic field will enhance the generation of free charges 29 , 31 .…”

Section: Resultsmentioning

confidence: 99%

“…where B is the external magnetic field, a are the hyperfine coupling constants and I are the hyperfine magnetic fields [23,28]. Both terms cause each of the spins to precess with a frequency gµ B B in such a way that when it happens in a randomly oriented spin environment such as that of hyperfine coupling, it induces spin flips that lead to transitions from the singlet to the triplet state, and backwards [26,29].…”

Section: Inter-system Crossing and Magnetic Field Effects On Electronmentioning

confidence: 99%

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Magnetic field enhancement of organic photovoltaic cells performance

Oviedo-Casado

Urbina

Prior

2017

Sci Rep

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Charge separation is a critical process for achieving high efficiencies in organic photovoltaic cells. The initial tightly bound excitonic electron-hole pair has to dissociate fast enough in order to avoid photocurrent generation and thus power conversion efficiency loss via geminate recombination. Such process takes place assisted by transitional states that lie between the initial exciton and the free charge state. Due to spin conservation rules these intermediate charge transfer states typically have singlet character. Here we propose a donor-acceptor model for a generic organic photovoltaic cell in which the process of charge separation is modulated by a magnetic field which tunes the energy levels. The impact of a magnetic field is to intensify the generation of charge transfer states with triplet character via inter-system crossing. As the ground state of the system has singlet character, triplet states are recombination-protected, thus leading to a higher probability of successful charge separation. Using the open quantum systems formalism we demonstrate that the population of triplet charge transfer states grows in the presence of a magnetic field, and discuss the impact on carrier population and hence photocurrent, highlighting its potential as a tool for research on charge transfer kinetics in this complex systems.

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“…Moreover, as the ground state has spin zero, direct recombination of triplet CT states is forbidden [10] and has to happen through an auxiliary triplet exciton state (|e, T ), hence the dissociation of free charges is in principle more efficient if it happens from triplet CT states.The necessary conversion from the initial singlet CT to the more convenient triplet CT -a process called inter-system crossing (ISC)-occurs either via hyperfine and spin-orbit coupling or due to wavefunction overlap, all of them too small to be relevant in OPVs. The alternative is to enhance spin flips employing an external magnetic field [17][18][19][20].…”

Section: Modelmentioning

confidence: 99%

Magnetic fields: a tool for the study of organic solar cells

Oviedo-Casado

Urbina

Prior

2018

Eur. Phys. J. Spec. Top.

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Charge transfer in polymer devices represents a crucial, though highly inaccessible stage of photocurrent generation. In this article we propose studying the properties and behaviour of organic solar cells through the modification of photocurrent generation when an external magnetic field is applied. By allowing the parameters of our theoretical model not to be constrained to any specific material, we are able to show that not only a modest external magnetic field leads to a significant increase in photocurrent intensity, but also how such magnetic field can be used to study in detail the energy levels and transition rates within the polymer compound. Systematic exploration of key properties in organic composites thus can lead to highly optimised devices in which a magnetic field produces an enhancement in the efficiency of polymer solar cells.

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CT-excitons and magnetic field effect in polydiacetylene crystals

Cited by 15 publications

References 11 publications

Optical Projection and Spatial Separation of Spin-Entangled Triplet Pairs from the S1 (21 Ag–) State of Pi-Conjugated Systems

Optical Projection and Spatial Separation of Spin-Entangled Triplet Pairs from the S1 (21 Ag–) State of Pi-Conjugated Systems

Magnetic field enhancement of organic photovoltaic cells performance

Magnetic fields: a tool for the study of organic solar cells

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