Electron Spin Echo of Photoinduced Spin-Correlated Polaron Pairs in P3HT:PCBM Composite

Uvarov, Mikhail N.; Кулик, Л. В.

doi:10.1007/s00723-012-0401-2

Cited by 18 publications

(18 citation statements)

References 24 publications

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“…The latter is responsible for the distance and orientation distributions which lead to averaging out of the modulation pattern in ESEEM signals. In spite of these challenges, authors of [186][187][188][189] were able to detect after a laser flash the two-pulse out-of-phase ESE at X-band in both composites with PC 61 BM and PC 71 BM, confirming the spin-correlated nature of these CT-states. In the case of P3HT:PC 61 BM the characteristic time of the out-of-phase ESE decay with increasing delay after laser flash is 0.5 μs at 65 K, which gives a lower limit of the lifetime of these states.…”

Section: Sequentialmentioning

confidence: 83%

“…Pulsed tr-EPR spectroscopy has also been employed to study the interfacial light-induced CT-states in P3HT:PC 61 BM and P3HT:PC 71 BM composites. [186][187][188][189] In general, time-resolved pulsed EPR spectroscopy is a powerful technique to study SCRP and has been widely used to characterize spin dynamics and geometry of SCRP in donor-acceptor systems at conventional, X-band and higher, Q-, W-, D-bands mw frequencies. [147,[174][175][190][191][192][193][194][195][196][197][198][199][200][201] Cw tr-EPR experiments are typically considerably more difficult at higher frequencies than X-band and have no yet been performed for BHJ systems.…”

Section: Sequentialmentioning

confidence: 99%

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Charge Transfer Processes in OPV Materials as Revealed by EPR Spectroscopy

Niklas

Poluektov

2017

Advanced Energy Materials

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Understanding charge separation and charge transport at a molecular level is crucial for improving the efficiency of organic photovoltaic (OPV) cells. Under illumination of Bulk Heterojunction (BHJ) blends of polymers and fullerenes, various paramagnetic species are formed including polymer and fullerene radicals, radical pairs, and photoexcited triplet states. Light-induced Electron Paramagnetic Resonance (EPR) spectroscopy is ideally suited to study these states in BHJ due to its selectivity in probing the paramagnetic intermediates. Advanced techniques like pulsed EPR and ENDOR spectroscopy allow the determination of hyperfine coupling tensors, while high-frequency EPR allows the EPR signals of the individual species to be resolved and their g-tensors to be determined. The magnetic resonance parameters of the various polymer donors reveal details about the delocalization of the positive polaron which is important for the efficient charge separation in BHJ systems. Time-resolved EPR can contribute to the study of the dynamics of charge separation, charge transfer and recombination in BHJ by probing the unique spectral signatures of charge transfer and triplet states. EPR also has the potential to allow characterization of intermediates and products of BHJ degradation.

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Section: Sequentialmentioning

confidence: 83%

Section: Sequentialmentioning

confidence: 99%

Charge Transfer Processes in OPV Materials as Revealed by EPR Spectroscopy

Niklas

Poluektov

2017

Advanced Energy Materials

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“…However, the latter often provide ambiguous results concerning spin-coupling, relaxation, and dynamics in some conjugated polymers 17−19 and in polymer:fullerene composites. 20,21 This is the reason why direct cw electron paramagnetic resonance (cw EPR) spectroscopy is widely used for a more detailed investigation of spin-assisted processes in various organic polymer systems at different frequencies of electron precession. 18,19,22−24 The multifrequency cw EPR method was used to analyze the impact of exchange interaction between polarons stabilized in polyaniline salt highly doped with para-toluenesulfonic acid (PANI:TSA) with guest air oxygen biradicals.…”

Section: Introductionmentioning

confidence: 99%

“…Because both charge carriers possess spins playing a crucial role in the properties of organic devices, the processes carried out in such systems can be studied by various continuous wave (cw) and pulse magnetic resonance methods. However, the latter often provide ambiguous results concerning spin-coupling, relaxation, and dynamics in some conjugated polymers − and in polymer:fullerene composites. , This is the reason why direct cw electron paramagnetic resonance (cw EPR) spectroscopy is widely used for a more detailed investigation of spin-assisted processes in various organic polymer systems at different frequencies of electron precession. ,,− The multifrequency cw EPR method was used to analyze the impact of exchange interaction between polarons stabilized in polyaniline salt highly doped with para -toluenesulfonic acid (PANI:TSA) with guest air oxygen biradicals. − PANI-TSA was analyzed to be a material built from relatively short helically formed chains that assemble within globular particles of size about 10 nm. Paramagnetic centers stabilized in the PANI bulk during doping with TSA were found to be more accessible for interaction with inside/guest radicals than with other polyaniline salts.…”

Section: Introductionmentioning

confidence: 99%

Impact of Spin-Exchange Interaction on Charge Transfer in Dual-Polymer Photovoltaic Composites

et al. 2020

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Magnetic resonance, relaxation, and dynamic parameters of spin-charge carriers photoinitiated in dual-polymer composites formed by narrow-band-gap poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(bithiophene)] (F8T2), poly[2,7-(9,9-dioctylfluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PFO-DBT), and poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) copolymers modified with [6,6]-phenyl-C61-butanoic acid methyl ester (PC61BM) as a photovoltaic spin subsystem and polyaniline salt doped with para-toluenesulfonic acid (PANI:TSA) as a guest spin subsystem were comparatively studied by the direct light-induced electron paramagnetic resonance (LEPR) spectroscopy in a wide photon energy and temperature range. Irradiation of dual-polymer composites by the photons leads to the formation in its photovoltaic subsystem of polarons and methanofullerene radical anions whose concentration and dynamics are determined by the density and energy of the initiating light photons. A part of such polarons first filled high-energetic spin traps formed in the matrix due to its disordering. A crucial role of exchange interaction between different spin ensembles in the charge excitation, relaxation, and transport in multispin narrow-band-gap composites was demonstrated. These processes were interpreted within the framework of hopping of polarons along copolymer chains of photovoltaic subsystems and their exchange interaction with neighboring spin ensembles. Such an interaction was shown to facilitate the transfer of charges and inhibit their recombination in multispin dual-polymer composites. The distribution of spin density over polymer chains in the dual-polymer composites with the π–π stacked architecture was analyzed in the framework of the density functional theory (DFT). It confirmed the transfer of electron spin density between neighboring polymer chains that made formation more likely of radical pairs in triplet state than in singlet one and inhibited their fast geminate recombination. Spin interactions eliminate the selectivity of these systems to the photon energy, extend the range of optical photons they absorb, and, therefore, increase their efficiency to converse the light energy. Handling electronic properties via intra- and intersubsystem spin interactions in such multispin composites allows one to create on their base more efficient and functional electronic and spintronic elements.

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“…At the 3 mm/84 GHz waveband spin echo EPR, a weak anisotropy of the g -factors and the line widths of polarons and counterions photoinitiated in the composite PBDB-T:ITIC was studied, and the main tensor values of these magnetic resonance parameters were evaluated . It should be noted, however, that the relaxation times of charge carriers determined by pulse EPR in some conjugated polymers − and polymer:fullerene composites , appeared to be more than 1–2 orders of magnitude slower than those determined by continuous wave (cw) EPR technique. Such discrepancy in the data obtained by pulse and cw methods can be due to a fundamental limitation inherent in the pulsed EPR technique, namely its deadtime around 100 ns, which prevents the registration of paramagnetic centers with very short relaxation times.…”

Section: Introductionmentioning

confidence: 99%

Light-Induced Electron Paramagnetic Resonance Study of Charge Transport in Fullerene and Nonfullerene PBDB-T-Based Solar Cells

et al. 2021

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We present a combined light-induced electron paramagnetic resonance (LEPR) study of photoinitiation, relaxation, and recombination of charge carriers initiated by achromatic/white (with a color temperature of 5000 K) and monochromatic (with a photon energy of 1.34–3.41 eV) light in PBDB-T-based photovoltaic systems with PC61BM, PC71BM, and ITIC-M counterions. Charge carriers, polarons on polymer chains, and respective radical anions excited in disordered composite matrixes first fill spin traps, the number, energy depth, and spatial distribution of which are determined by the structure and crystallinity of bulk heterojunctions. By deconvolution of the effective LEPR spectra, the contributions of immobilized and mobile charge carriers, as well as their main magnetic resonance parameters, were determined separately at a wide variety of experimental conditions. The interaction of spins occupying different energy levels in the bandgap of a polymer semiconductor provokes the extreme photon energy sensitivity of the spin-assisted processes carried out in the polymer composites. The density functional theory calculations of the millimeter-waveband LEPR spectrum allowed the conclusion that polarons photoinitiated in the PBDB-T backbone are delocalized over its 4–5 monomers. Side π–π-stack packaging and S-isomerization of electron acceptors were also found. Predominant nongeminate recombination of charge carriers follows multistep trapping–detrapping spin hopping between sites of polymer layers and is strongly governed by the number, energy depth, and spatial distribution of spin traps. It was shown that all spin-involving processes in composites are spin-assisted and, therefore, are determined by the main magnetic resonance properties of both the spin charge carriers. The stability of charge carriers in a polymer-based composite was demonstrated to increase by more than an order of magnitude in the series of radical anions PC61BM–• → ITIC-M–• → PC71BM–•. A further improvement in the functionality of the composite occurs at its slight 2,5-diphenyloxazole modification. The use of low-dimensional ITIC-M instead of PCBM and/or PPO with extended π-system significantly increases the exchange interaction between the spin charge carriers situated on the adjacent layers of the composite. This blocks intrachain charge diffusion but accelerates its interlayer hopping in the polymer matrix, which increases the efficiency and functionality of the composite.

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Electron Spin Echo of Photoinduced Spin-Correlated Polaron Pairs in P3HT:PCBM Composite

Cited by 18 publications

References 24 publications

Charge Transfer Processes in OPV Materials as Revealed by EPR Spectroscopy

Charge Transfer Processes in OPV Materials as Revealed by EPR Spectroscopy

Impact of Spin-Exchange Interaction on Charge Transfer in Dual-Polymer Photovoltaic Composites

Light-Induced Electron Paramagnetic Resonance Study of Charge Transport in Fullerene and Nonfullerene PBDB-T-Based Solar Cells

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