Dispersive dynamics of photoexcitations in conjugated polymers measured by photomodulation spectroscopy

Epshtein, O.; Nakhmanovich, G.; Eichen, Yoav; Ehrenfreund, E.

doi:10.1103/physrevb.63.125206

Cited by 71 publications

(72 citation statements)

References 20 publications

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“…At higher frequencies, the logðDT =T Þ-log(frequency) plot approaches a slope of )1. This is expected for monomolecular and bimolecular decay processes [6]. For stretched exponential decay, however, a slope between 0 and )1 is expected.…”

Section: Resultsmentioning

confidence: 75%

“…The ratio DT =T is proportional to the absorbance change (ÀDT =T ¼ lnð10Þ Â DA). PIA spectroscopy is frequently used in the field of conjugated polymers to investigate the nature and recombination kinetics of photogenerated species [5,6]. Recently, PIA measurements at a single wavelength in the near-infrared (frequency-resolved modulated www.elsevier.com/locate/cplett transmission) have been used to study dye-sensitized solar cells [7,8].…”

Section: Introductionmentioning

confidence: 99%

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Photoinduced absorption spectroscopy of dye-sensitized nanostructured TiO2

Boschloo

Hagfeldt

2003

Chemical Physics Letters

110

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Photoinduced absorption (PIA) spectroscopy was used to investigate dye-sensitized electrodes and solar cells under illumination conditions comparable to sunlight. In the absence of redox electrolyte, cis-RuðdcbpyÞ 2 ðNCSÞ 2 -sensitized nanostructured TiO 2 films show a long-lived photoinduced charge-separation (oxidized dye molecules/injected electrons in TiO 2 ), with a lifetime of about 10 À3 s under full sun illumination. The PIA spectrum of a complete dye-sensitized cell is due to electrons in TiO 2 and iodine radicals (I À 2 ) in the electrolyte. The lifetime of this charge-separated state at opencircuit conditions was determined to be 0.15 s (0.27 sun illumination).

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Section: Resultsmentioning

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Photoinduced absorption spectroscopy of dye-sensitized nanostructured TiO2

Boschloo

Hagfeldt

2003

Chemical Physics Letters

110

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“…[28] Both components depend linearly on the pump intensity I p and cross at wt = 1, where f = w/2p is the applied modulation frequency of a sinusoidal excitation. The generation efficiency g and the detection efficiency are summarized by h. In Figure 4, we show the modulation frequency scan of the PA of DCV3T and DCV3T: C 60 at 1.5 eV.…”

Section: Triplet-state Recombination Dynamicsmentioning

confidence: 99%

“…Due to a limited chopper frequency ( 6 kHz), we were not able to study the phase shift above the intersection frequency (wt @ 1), which would allow a more-precise fitting procedure, for example, via assuming dispersive recombination. [28] By means of transient absorption (TA) measurements, the decay time is more precisely determined. In Figure 5 a, the TA of the single and blend layer are given.…”

Section: Triplet-state Recombination Dynamicsmentioning

confidence: 99%

Enhanced Photogeneration of Triplet Excitons in an Oligothiophene–Fullerene Blend

Schueppel¹,

Uhrich²,

Pfeiffer

et al. 2007

ChemPhysChem

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Photoinduced and transient absorption spectroscopy is used to study triplet exciton dynamics in thin films of a new thiophene-based oligomer (DCV3T) and blends of DCV3T and fullerene C60. We find enhanced DCV3T triplet exciton generation in the blend layer, which is explained as an excitonic ping-pong effect: singlet energy transfer from DCV3T to C60, followed by immediate intersystem crossing to C60, and triplet exciton back-transfer. Estimations of the rate constants involved show that the ping-pong effect has an overall efficiency close to unity. The singlet-singlet energy transfer from DCV3T to C60 is demonstrated by efficient quenching of DCV3T luminescence in the blend, leading to sensitized emission of C60. We discuss a promising new concept of solar cells with an enlarged active-layer thickness based on potentially long-ranged triplet exciton diffusion in combination with efficient intersystem crossing.

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“…Combining the triplet cross section, differential transmission and penetration depth, we deduce a triplet density in the triblock thin- To better understand the recombination mechanism of the excited species in the material systems studied, both the dependence of the PA signal on pump intensity and the applied modulation frequency have been studied as shown in Figure 8(b). We find that both the triblock 3a and the 2:1 F8BT/PFM blend are characterized by dispersive dynamics 52 resulting from a distribution of excited state lifetimes. Typically, rather than the N I x 22 form expected for the inphase PA signal in the case of a uniform recombination rate, these systems display a gentle, high-frequency roll-off of the form N I x 2a where 0 < a < 1, with lower values of a implying a more disperse distribution of lifetimes.…”

mentioning

confidence: 98%

Photophysics and morphology of a polyfluorene donor–acceptor triblock copolymer for solar cells

Yan

Cadby

Parnell

et al. 2013

J Polym Sci B Polym Phys

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We present a study of the optical, structural and device properties of a polyfluorene (PFM)-based (PFM-F8BT-PFM) donor-acceptor triblock copolymer for use in an organic solar cell. Neutron reflectivity is employed to probe the vertical composition profile before and after thermal annealing while the crystallinity was examined using grazing incidence wideangle X-ray. The absorption spectra and photoluminescence emission for the triblock and analogous blend of PFM with F8BT reveal a greater degree of intermixing in the triblock. However, the triblock copolymer exhibits exciplex emission, which necessitates a geminate polar pair; long-lived exciplex states are detrimental in organic photovoltaic devices. The triplet yield in the triblock and the blend is estimated using photoinduced absorption, with the triblock copolymer generating a triplet population 20 times that of the blend. This is far from ideal as triplets are wasted states in organic photovoltaic devices and they can also act as scavengers of polarons reducing the efficiency even more. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1705-1718 KEYWORDS: block copolymers; conjugated polymers; morphology; organic photovoltaics; photophysics; solar cells INTRODUCTION Organic photovoltaic (OPV) devices have inspired significant academic and industrial excitement due to the possibility of producing large-scale, low-cost renewable energy. These factors make mass-produced thin film conjugated polymer solar cells highly attractive to tackle the problem of dwindling fossil fuels and the need to decarbonize the world economy. The power conversion efficiency (PCE) of OPV devices has increased steadily in the last decade and the best current single junction polymer device efficiencies range from 7 to 9% and have been achieved using a blend of an alternating copolymer of thieno [3,4-b]thiophene and benzodithophene (known as PTB7) with the soluble fullerene PC 71 BM.1 Further work has demonstrated that PTB7-based OPV devices can produce inverted devices with an efficiency of 9.2%.

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Dispersive dynamics of photoexcitations in conjugated polymers measured by photomodulation spectroscopy

Cited by 71 publications

References 20 publications

Photoinduced absorption spectroscopy of dye-sensitized nanostructured TiO2

Photoinduced absorption spectroscopy of dye-sensitized nanostructured TiO2

Enhanced Photogeneration of Triplet Excitons in an Oligothiophene–Fullerene Blend

Photophysics and morphology of a polyfluorene donor–acceptor triblock copolymer for solar cells

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