Charge Transfer–Mediated Singlet Fission

Monahan, Nicholas R.; Zhu, Xiaoyang

doi:10.1146/annurev-physchem-040214-121235

Cited by 271 publications

(425 citation statements)

References 80 publications

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“…7 In such systems, photoexcitation to S 1 typically results in rapid decay of the singlet state, via an intermediate state with multiexciton character, resulting in the formation of two T 1 states on adjacent chromophores. [8][9][10][11] In solar energy converters, SF can recoup some of the energy normally lost to thermalisation, as long as the triplet excitons can be efficiently converted to charge carriers. SF is a particularly attractive means of multiple exciton generation for high-efficiency concepts, because unlike nanocrystalline downconverters, the optical gap of SF materials is equal to the onset energy of efficient carrier multiplication.…”

Section: Introductionmentioning

confidence: 99%

Crystalline silicon solar cells with tetracene interlayers: the path to silicon-singlet fission heterojunction devices

et al. 2018

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Singlet exciton fission is an exciton multiplication process that occurs in certain organic materials, converting the energy of single highly-energetic photons into pairs of triplet excitons. This could be used to boost the conversion efficiency of crystalline silicon solar cells by creating photocurrent from energy that is usually lost to thermalisation. An appealing method of implementing singlet fission with crystalline silicon is to incorporate singlet fission media directly into a crystalline silicon device. To this end, we developed a solar cell that pairs the electron-selective contact of a high-efficiency silicon heterojunction cell with an organic singlet fission material, tetracene, and a PEDOT:PSS hole extraction layer. Tetracene and n-type crystalline silicon meet in a direct organic-inorganic heterojunction. In this concept the tetracene layer selectively absorbs blue-green light, generating triplet pairs that can dissociate or resonantly transfer at the organo-silicon interface, while lower-energy light is transmitted to the silicon absorber. UV photoemission measurements of the organicinorganic interface showed an energy level alignment conducive to selective hole extraction from silicon by the organic layer. This was borne out by current-voltage measurements of devices subsequently produced. In these devices, the silicon substrate remained well-passivated beneath the tetracene thin film. Light absorption in the tetracene layer created a net reduction in current for the solar cell, but optical modelling of the external quantum efficiency spectrum suggested a small photocurrent contribution from the layer. This is a promising first result for the direct heterojunction approach to singlet fission on crystalline silicon.

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Section: Introductionmentioning

confidence: 99%

Crystalline silicon solar cells with tetracene interlayers: the path to silicon-singlet fission heterojunction devices

et al. 2018

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“…[13][14][15][16][17][18][19][20][21] Numerous investigations have revealed that the interaction between the initial singlet exciton (SE) state and TT state, which plays an important role in SF dynamics, may include a direct statestate interaction and an indirect superexchange interaction mediated by a charge-transfer (CT) state. 3,4,[22][23][24][25][26][27][28][29][30][31][32] This interaction in organic crystals can be strong enough to induce the quantum coherence between SE and TT states, 5,7,33,34 resulting in an ultrafast timescale of SF.…”

Section: Introductionmentioning

confidence: 99%

Effects of Charge Transfer State and Exciton Migration on Singlet Fission Dynamics in Organic Aggregates

Zang

Zhao

et al. 2016

J. Phys. Chem. C

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A time-dependent wavepacket diffusion method is used to investigate the effects of charge transfer (CT) states, singlet exciton and multiexciton migrations on singlet fission (SF) dynamics in organic aggregates. The results reveal that the incorporation of CT states can result in a different SF dynamics from the direct interaction between singlet exciton and multiexciton, and an obvious SF interference is also observed between the direct channel and the indirect channel mediated by CT states. In the case of direct interaction, although the fast population transfer of singlet exciton in monomers, by the increase of exciton-exciton interaction, can accelerate the SF process, the spatial coherence alternatively has a counter-productive effect, and their competition leads to an optimal exciton-exciton interaction at which SF has a maximal rate. This trade-off relationship in SF dynamics is further analysed from different perspectives, specifically in spatial and energy representations, is also confirmed through the indication that static energy disorders can speed up SF process by destructing the coherence.Meanwhile, it is found that the couplings among multiexciton states decrease SF rates by the multiexciton coherence and backward conversion from multiexciton to singlet exciton states.

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“…In tetracene crystals, where SF is endoergic but still highly efficient, the reverse processtriplet−triplet upconversionreadily follows, resulting in delayed fluorescence. 11,12 While most studies to date have addressed SF processes in small-molecular crystals of films, a few reports have been dedicated to intermolecular and even intramolecular SF in solution. Walker et al, 13 for example, report the occurrence of singlet exciton fission in a 6,13-bis (triisopropylsilylethinyl)-pentacene (TIPS-pentacene) excimer in solution.…”

Section: Introductionmentioning

confidence: 99%

Singlet Fission in Quinoidal Oligothiophenes

et al. 2016

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The electronic properties of quinoidal oligithiophenes make them interesting for applications in semiconductor technology. Because of their very large singlet− triplet splitting, they are promising candidates for singlet fission (SF), a process in which an initially excited singlet state is converted into two triplet excitons. Thus, the efficiency of solar cells could be increased to overcome the ShockleyQueisser limit. Here, we investigate the ability of a quinoidal bithiophene to undergo SF in solution. We calculated the ground state and low-lying excited states using a combined density functional theory and multireference configuration interaction approach including dispersion corrections. Potential energy curves along normal mode displacements were computed to detect avoided crossings between the initially excited bright singlet state and a dark doubly excited state which can be interpreted as a triplet pair overall coupled to a singlet 1 (TT). The studied quinoidal bithiophene meets the energetic requirement for SF. A path enabling intramolecular SF could not be found. In contrast, we were able to identify two vibrational modes relevant for an intermolecular SF process in the slip-stacked dimer: A promoting coordinate that couples a bright singlet state with the 1 (TT) state and a separating coordinate that localizes the triplet states on the respective monomers. These results elucidate the mechanism underlying the formation of a triplet pair and the separation of the triplet excitons after initial photoexcitation of the bright singlet state.

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Charge Transfer–Mediated Singlet Fission

Cited by 271 publications

References 80 publications

Crystalline silicon solar cells with tetracene interlayers: the path to silicon-singlet fission heterojunction devices

Crystalline silicon solar cells with tetracene interlayers: the path to silicon-singlet fission heterojunction devices

Effects of Charge Transfer State and Exciton Migration on Singlet Fission Dynamics in Organic Aggregates

Singlet Fission in Quinoidal Oligothiophenes

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