Photoexcitation dynamics in an alternating polyfluorene copolymer

Westerling, M.; Aarnio, Harri; Österbacka, Ronald; Stubb, H.; King, Simon; Monkman, Andrew P.; Andersson, Mats R.; Jespersen, Kim G.; Kesti, Tero; Yartsev, Arkady; Sundström, Villy

doi:10.1103/physrevb.75.224306

Cited by 25 publications

(36 citation statements)

References 49 publications

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“…Numerous recent reports have shown that charges can be photogenerated in a single material to some extent 10, 18, 24, 33. Even without heterojunction interfaces, charge photogeneration can be induced from the energetic disorder present in different polymer microstructures (e.g., in P3HT),24 by the strong donor–acceptor character of a given polymer33 or by the presence of ions 10. In the latter case, we have shown that charge‐transfer states formed in the Coulomb field of ions have a PIA feature resonant with exciton emission, resulting in pronounced ECA under pulsed excitation.…”

Section: Resultsmentioning

confidence: 99%

Exciton‐Charge Annihilation in Organic Semiconductor Films

Hodgkiss

Albert‐Seifried

Rao

et al. 2012

Adv Funct Materials

104

134

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Time‐resolved optical spectroscopy is used to investigate exciton‐charge annihilation reactions in blended films of organic semiconductors. In donor–acceptor blends where charges are photogenerated via excitons, pulsed optical excitation can deliver a sufficient density of temporally overlapping excitons and charges for them to interact. Transient absorption spectroscopy measurements demonstrate clear signatures of exciton‐charge annihilation reactions at excitation densities of ≈1018 cm−3. The strength of exciton‐charge annihilation is consistent with a resonant energy transfer mechanism between fluorescent excitons and resonantly absorbing charges, which is shown to generally be strong in organic semiconductors. The extent of exciton‐charge annihilation is very sensitive not only to fluence but also to blend morphology, becoming notably strong in donor–acceptor blends with nanomorphologies optimized for photovoltaic operation. The results highlight both the value of transient optical spectroscopy to interrogate exciton‐charge annihilation reactions and the need to recognize and account for annihilation reactions in other transient optical investigations of organic semiconductors.

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Section: Resultsmentioning

confidence: 99%

Exciton‐Charge Annihilation in Organic Semiconductor Films

Hodgkiss

Albert‐Seifried

Rao

et al. 2012

Adv Funct Materials

104

134

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“…Generation of charges is feasible also in the neat polymer, with a yield of 12%-13%, through singlet exciton dissociation but also through exciton-exciton fusion and subsequent reactions. The delayed fluorescence observed in this polymer is most probably [14] due to polaron pair geminate recombination on the longer time scale. In APFO-Green polymers designed for extended absorption into the near infrared range, semi-empirical ZINDO calculations once more contribute well, to the point that predictions of optical oscillator energies and amplitudes from the quantum chemical modeling can be used to fit the experimentally observed dielectric function of the polymers APFO-Green1 and APFO-Green2.…”

Section: Electronic Structure As Seen Through Optical Absorption Andmentioning

confidence: 90%

“…The steady-state absorption and emission spectra are therefore due to these states; excitation spectra can be affected also by dark intermediate energy states. Photophysical studies of the polymer [14] contribute to the description of the transport and reactions of excitons in the neat polymer. Generation of charges is feasible also in the neat polymer, with a yield of 12%-13%, through singlet exciton dissociation but also through exciton-exciton fusion and subsequent reactions.…”

Section: Electronic Structure As Seen Through Optical Absorption Andmentioning

confidence: 99%

Polymer Photovoltaics with Alternating Copolymer/Fullerene Blends and Novel Device Architectures

Inganäs¹,

Zhang²,

Tvingstedt³

et al. 2010

Advanced Materials

100

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The synthesis of novel conjugated polymers, designed for the purpose of photovoltaic energy conversion, and their properties in polymer/fullerene materials and photovoltaic devices are reviewed. Two families of main-chain polymer donors, based on fluorene or phenylene and donor-acceptor-donor comonomers in alternating copolymers, are used to absorb the high-energy parts of the solar spectrum and to give high photovoltages in combinations with fullerene acceptors in devices. These materials are used in alternative photovoltaic device geometries with enhanced light incoupling to collect larger photocurrents or to enable tandem devices and enhance photovoltage.

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“…The PA 1 bands in the near‐infrared (IR) in the three samples were assigned to singlet excited state absorption, a transition from the lowest singlet exciton to a higher energy state. The PA 2 band, which displayed a slower temporal evolution, was attributed to polaron and/or polaron pair absorption, which has been observed in other π‐conjugated polymers and D–A copolymers 16–18. The peak position of the PA 1 band for P3 was located around 1000 nm, whereas the corresponding peaks for other two polymers ( P1 and P2 ) were longer than 1050 nm.…”

Section: Resultsmentioning

confidence: 67%

Effects of substituted side‐chain position on donor–acceptor conjugated copolymers

Lee

Cho

Tong

et al. 2011

J. Polym. Sci. A Polym. Chem.

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The optical properties and electrical properties of a series of low‐band‐gap conjugated copolymers, in which alkyl side chains were substituted at various positions, were investigated using donor–acceptor conjugated copolymers consisting of a cyclopentadithiophene derivative and dithienyl‐benzothiadiazole. With substituted side chains, the intrinsic properties of the copolymers were significantly altered by perturbations of the intramolecular charge transfer. The absorption of poly[2, 6‐(4,4‐bis(2‐octyl)‐4H‐cyclopenta‐[2,1‐b:3,4‐b′]dithiophene)‐alt‐4, 7‐bis(4‐octyl‐thiophene‐2‐yl)benzo‐2,1,3‐thiadiazole] [PCPDT‐ttOTBTOT (P2)], which assumed a tail–tail configuration, tended to blue shift relative to the absorption of poly[2,6‐(4,4‐bis(2‐octyl)‐4H‐cyclopenta‐[2,1‐b:3,4‐b′]dithiophene)‐alt‐4,7‐bis (thiophene‐2‐yl)benzo‐2,1,3‐thiadiazole] [PCPDT‐TBTT (P1)]. The absorption of poly[2,6‐(4,4‐bis(2‐octyl)‐4H‐cyclopenta‐[2,1‐b:3, 4‐b′]dithiophene)‐alt‐4,7‐bis(3‐octyl‐thiophene‐2‐yl)benzo‐2,1,3‐thiadiazole] [PCPDT‐hhOTBTOT (P3)], which assumed a head–head configuration, was blue shifted relative to that of P2. The electrical transport properties of field‐effect transistors were sensitive to the side chain position. The field‐effect mobility in P2 (μ2 = 1.8 × 10−3 cm2/V s) was slightly lower than that in P1 (μ1 = 4.9 × 10−3 cm2/V s). However, the mobility of P3 was very low (μ3 = 3.8 × 10−6 cm2/V s). Photoexcitation spectroscopy showed that the charge generation efficiency (shown in transient absorption spectra) and polaron pair mobility in P1 and P2 were higher than in P3, yielding P1 and P2 device performances that were better than the performance of devices based on P3. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

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Photoexcitation dynamics in an alternating polyfluorene copolymer

Cited by 25 publications

References 49 publications

Exciton‐Charge Annihilation in Organic Semiconductor Films

Exciton‐Charge Annihilation in Organic Semiconductor Films

Polymer Photovoltaics with Alternating Copolymer/Fullerene Blends and Novel Device Architectures

Effects of substituted side‐chain position on donor–acceptor conjugated copolymers

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