Bimolecular radiationless transitions in crystalline tetracene

Swenberg, Charles E.; Stacy, W. T.

doi:10.1016/0009-2614(68)80087-9

Cited by 209 publications

(169 citation statements)

References 11 publications

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“…Emission from lower energy excimer-like species then persists for >10 ns. Our results suggest that despite its herringbone crystal motif, DIP does not support phenomena like long-lived singlet exciton states (as in crystalline anthracene 24,25 ) or singlet fission (as in crystalline perylenes, 26,27 tetracene, 28,29 and pentacene 30−32 ) seen in crystals with similar packing motifs. Instead, rapid internal conversion leads to transient heating, with a small fraction (<10%) of the excitons surviving in longer-lived trap or defect states.…”

Section: ■ Introductionmentioning

confidence: 77%

Excited-State Dynamics of Diindenoperylene in Liquid Solution and in Solid Films

et al. 2015

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The excited-state dynamics of diindenoperylene (DIP) are investigated in dilute solution and in a solid film at room temperature using picosecond photoluminescence and femtosecond transient absorption measurements. In solution, DIP undergoes a rapid (0.89 ns) internal conversion back to its ground state, with no detectable formation of triplet or other long-lived states. In the solid state, multiple emissive species are formed. The time-resolved photoluminescence signal is dominated by an intrinsic exciton that decays on a time scale of 166 ps. Emission from lower energy excimer-like species then persists for >10 ns. Transient absorption experiments indicate that the majority of the excited-state population relaxes to the ground state on the 166 ps time scale, but a smaller fraction (<10%) survives in longer-lived trap or defect states. The rapid internal conversion leads to transient heating that results in a derivative line shape in the transient absorption signal at longer delays. DIP does not appear to support long-lived singlet exciton states or singlet fission. The implications of these results for the function of DIP in organic solar cells are discussed. ■ INTRODUCTIONOrganic molecular semiconductors are used in electronic devices ranging from transistors to solar cells. One advantage of organic semiconductors is the variety of molecular structures and interfaces that can give rise to different material properties. 1 The rylene family comprises a class of molecules that crystallize easily, have high stability, and support long exciton and charge carrier diffusion lengths. Diindenoperylene (DIP), whose structure is shown in Figure 1, is an extended rylene whose solid-state thin films have been extensively studied. 2−12 Its high degree of order, coupled with its excellent charge transport properties, have made it an increasingly popular choice as a component of organic photovoltaic (OPV) devices. 13−16 Furthermore, DIP has the ability to form crystalline mixtures with other conjugated molecules like perfluoropentacene or pentacene, opening up the possibility of making well-defined composite materials. 17−21 Despite its use in OPVs, much remains unclear in terms of DIP's basic photophysics. Since DIP's contribution to the photocurrent in an OPV should be determined at least in part by its exciton diffusion length, which in turn is determined by its excited-state lifetime, an improved understanding of its molecular photophysics is important for understanding how this material functions in an OPV.In this paper, we investigate the excited-state dynamics of DIP in both dilute solution and in a polycrystalline solid film at room temperature. In solution, DIP undergoes internal conversion back to the ground state on a subnanosecond time scale. This rapid internal conversion, seen in other acene molecules that incorporate a five-membered ring, has been attributed to a lack of resonance stabilization. 22,23 In solid form, DIP exhibits a complex decay that involves multiple emitting species. The time-resolved pho...

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Section: ■ Introductionmentioning

confidence: 77%

Excited-State Dynamics of Diindenoperylene in Liquid Solution and in Solid Films

et al. 2015

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“…Singlet fission requires the ability to host two triplets -for example, a dimer, molecular crystal, or a polymeric molecule. The earliest examples of SF were reported for polyacenes such as tetracene and pentacene [92,93]. Active research in this area seeks to design molecular chromophores specifically for efficient SF [94,95].…”

Section: Future Directionsmentioning

confidence: 99%

Multiple exciton generation in semiconductor nanocrystals: Toward efficient solar energy conversion

Beard¹,

Ellingson²

2008

Laser & Photonics Reviews

142

131

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Within the range of photon energies illuminating the Earth's surface, absorption of a photon by a conventional photovoltaic semiconductor device results in the production of a single electron-hole pair; energy of a photon in excess of the semiconductor's bandgap is efficiently converted to heat through electron and hole interactions with the crystal lattice. Recently, colloidal semiconductor nanocrystals and nanocrystal films have been shown to exhibit efficient multiple electron-hole pair generation from a single photon with energy greater than twice the effective band gap. This multiple carrier pair process, referred to as multiple exciton generation (MEG), represents one route to reducing the thermal loss in semiconductor solar cells and may lead to the development of low cost, high efficiency solar energy devices. We review the current experimental and theoretical understanding of MEG, and provide views to the nearterm future for both fundamental research and the development of working devices which exploit MEG. MEG E g E hνAbsorption of a single photon with energy in excess of two times the band gap, Eg, produces multiple excitons at the band edge. TEM picture of typical PbSe nanocrystals.

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“…Whereas singlet fission in pentacene is exothermic by ∼100 meV (1), in tetracene it is found to be endothermic by ∼180 meV (1,(19)(20)(21). Accordingly, triplet formation is significantly faster in pentacene films (∼80 fs) (5) than in tetracene (∼90 ps) (22), although curiously in the latter material the process remains highly efficient and fully independent of temperature (22,23).…”

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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.

194

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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Bimolecular radiationless transitions in crystalline tetracene

Cited by 209 publications

References 11 publications

Excited-State Dynamics of Diindenoperylene in Liquid Solution and in Solid Films

Excited-State Dynamics of Diindenoperylene in Liquid Solution and in Solid Films

Multiple exciton generation in semiconductor nanocrystals: Toward efficient solar energy conversion

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

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