Triplet diffusion in singlet exciton fission sensitized pentacene solar cells

Tabachnyk, Maxim; Ehrler, Bruno; Bayliss, Sam L.; Friend, Richard H.; Greenham, Neil C.

doi:10.1063/1.4824420

Cited by 70 publications

(88 citation statements)

References 27 publications

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“…(1) is true for organic crystalline materials like pentacene and hexacene derivatives, the former being the most studied material for SF purposes. 3,9,[17][18][19][20][21][22][23][24][25] For hexacene, instead, a possible fission of the singlet in three triplets has been recently proposed, due to the extremely low energy of T1. 26 However, hexacene is very unstable 27 and, for this reason, is usually functionalized.…”

Section: Introductionmentioning

confidence: 99%

Singlet fission in linear chains of molecules

Ambrosio

Troisi

2014

The Journal of Chemical Physics

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We develop a model configuration interaction Hamiltonian to study the electronic structure of a chain of molecules undergoing singlet fission. We first consider models for dimer and trimers and then we use a matrix partitioning technique to build models of arbitrary size able to describe the relevant electronic structure for singlet fission in linear aggregates. We find that the multi-excitonic state (ME) is stabilized at short inter-monomer distance and the extent of this stabilization depends upon the size of orbital coupling between neighboring monomers. We also find that the coupling between ME states located on different molecules is extremely small leading to bandwidths in the order of ~10meV. This observation suggests that multi-exciton states are extremely localized by electron-phonon coupling and that singlet fission involves the transition between a relatively delocalized Frenkel exciton and a strongly localized multi-exciton state. We adopt the methodology commonly used to study non-radiative transitions to describe the singlet fission dynamics in these aggregates and we discuss the limit of validity of the approach. The results indicate that the phenomenology of singlet fission in molecular crystals is different in many important ways from what is observed in isolated dimers.

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Section: Introductionmentioning

confidence: 99%

Singlet fission in linear chains of molecules

Ambrosio

Troisi

2014

The Journal of Chemical Physics

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“…52,65,68,[72][73][74][75][76][77] Here, it is important to distinguish between the contributions of triplet and singlet excitons to photocurrent. The effect of triplet-triplet annihilation also leads to inaccuracies as discussed above.…”

Section: (3) Photocurrent In Solar Cellsmentioning

confidence: 99%

Triplet transport in thin films: fundamentals and applications

Tang

2017

Chem. Commun.

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Triplet excitons are key players in multi-excitonic processes like singlet fission and triplet-triplet annihilation based photon upconversion, which may be useful in next-generation photovoltaic devices, photocatalysis and bioimaging. Here, we present an overview of experimental and theoretical work on triplet energy transfer, with a focus on triplet transport in thin films. We start with the theory describing Dexter-mediated triplet energy transfer and the fundamental parameters controlling this process. Then we summarize current experimental methods used to measure the triplet exciton diffusion length. Finally, the use of hierarchically ordered structures to improve the triplet diffusion length is presented, before concluding with an outlook on the remaining challenges.

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“…Incorporating singlet fission material within a lowband-gap solar cell should make it possible to capture the energy normally lost to thermalization following the absorption of highenergy photons (11,12). An external quantum efficiency of 129% (13) and an internal quantum efficiency of >180% (14) have been reported using pentacene as the singlet fission material and fullerene (C 60 ) as electron acceptor. Despite such significant advances, many questions remain about the underlying mechanism of triplet formation, such as the role of intermediate electronic states and the ability of systems to undergo endothermic fission.…”

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confidence: 99%

Identification of a triplet pair intermediate in singlet exciton fission in solution

Stern

Musser

Gélinas

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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190

260

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Singlet exciton fission is the spin-conserving transformation of one spin-singlet exciton into two spin-triplet excitons. This exciton multiplication mechanism offers an attractive route to solar cells that circumvent the single-junction Shockley-Queisser limit. Most theoretical descriptions of singlet fission invoke an intermediate state of a pair of spin-triplet excitons coupled into an overall spinsinglet configuration, but such a state has never been optically observed. In solution, we show that the dynamics of fission are diffusion limited and enable the isolation of an intermediate species. In concentrated solutions of bis(triisopropylsilylethynyl)[TIPS]-tetracene we find rapid (<100 ps) formation of excimers and a slower (∼10 ns) break up of the excimer to two triplet exciton-bearing free molecules. These excimers are spectroscopically distinct from singlet and triplet excitons, yet possess both singlet and triplet characteristics, enabling identification as a triplet pair state. We find that this triplet pair state is significantly stabilized relative to free triplet excitons, and that it plays a critical role in the efficient endothermic singlet fission process.T he fission of photogenerated spin-singlet excitons into pairs of spin-triplet excitons is an effective way to generate triplet excitons in organic materials (1, 2). Because the triplets produced are coupled into an overall singlet state, spin is conserved and triplet formation can proceed on sub-100-fs timescales (1, 3-5) with yields of up to 200% (1, 6, 7). Current interest in singlet fission is driven by its potential to improve the efficiency of solar cells by circumventing the Shockley-Queisser limit for single-junction devices (8-10). Incorporating singlet fission material within a lowband-gap solar cell should make it possible to capture the energy normally lost to thermalization following the absorption of highenergy photons (11,12). An external quantum efficiency of 129% (13) and an internal quantum efficiency of >180% (14) have been reported using pentacene as the singlet fission material and fullerene (C 60 ) as electron acceptor. Despite such significant advances, many questions remain about the underlying mechanism of triplet formation, such as the role of intermediate electronic states and the ability of systems to undergo endothermic fission.The basis of most kinetic descriptions of singlet fission is the triplet pair state 1 (TT), which is entangled into an overall singlet and is an essential intermediate for the formation of two free triplet excitons (1, 15). Whether this intermediate state is present only transiently, as expected in exothermic systems such as pentacene, or whether it can be sufficiently long lived to also play a central role in the fission process in slower systems is unclear. Transient absorption measurements of the canonical systems pentacene and tetracene in the solid state allow clear identification of only the singlet and triplet states (3,6,16,17), meaning the character of any intermediate has not been ob...

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Triplet diffusion in singlet exciton fission sensitized pentacene solar cells

Cited by 70 publications

References 27 publications

Singlet fission in linear chains of molecules

Singlet fission in linear chains of molecules

Triplet transport in thin films: fundamentals and applications

Identification of a triplet pair intermediate in singlet exciton fission in solution

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