Light-induced EPR study of spin-assisted charge transport in PFOT:PC61BM composite

Krinichnyi, V.I.; Yudanova, Evgeniya I.; Bogatyrenko, V. R.

doi:10.1016/j.jphotochem.2018.12.032

Cited by 4 publications

(18 citation statements)

References 23 publications

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“…Figure shows exemplary X-band LEPR spectra of the PANI:TSA/F8T2:PC 61 BM, PANI:TSA/PFO-DBT:PC 61 BM, and PANI:TSA/PCDTBT:PC 61 BM BHJ backgrounds irradiated by monochromatic sources with various photon energies h ν ph at T = 77 K. Figure exhibits the analogous spectra of the samples illuminated by white light with different correlated color temperatures (CCTs) T c . Earlier, it was shown − that at this waveband, the F8T2:PC 61 BM, PFO-DBT:PC 61 BM, and PCDTBT:PC 61 BM BHJ demonstrate doublet LEPR spectra of organic paramagnetic centers formed as a result of dissociation of photoinitiated excitons. As in the case of other similar photovoltaic composites, the low-field component of these spectra was attributed to polarons, formed on the copolymer chains, whereas the high-field spectral line refers to methanofullerene radical anions situated between these chains.…”

Section: Resultsmentioning

confidence: 83%

“…Deconvolution of effective cw LEPR spectra of a multispin system should be able to determine the main magnetic resonance parameters separately for all mobile and captured spin-charge carriers and analyze them upon variation of experimental conditions. Indeed, such a procedure allows one to estimate the composition, spatial distribution, and local concentration of spin-charge carriers excited in different organic photovoltaic composites, including narrow-band-gap mono-copolymer composites formed by F8T2, poly[2,7-(9,9-dioctylfluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PFO-DBT), and PCDTBT copolymers with PC 61 BM electron acceptors, − BHJ of various poly(3-alkylthiophenes):C 60 embedded into the conducting poly(2,5-dioctyloxy-phenylene vinylene) matrix (P3AT:C 60 /OOPPV) as well as dual-polymer composites formed by PC 61 BM-modified poly(3-dodecylthiophene) and PANI:TSA (PANI:TSA/P3DDT:PC 61 BM). , Paramagnetic susceptibility of spin-charge carriers photoinitiated in the latter dual-polymer composites was determined from their cw LEPR spectra to follow antiferromagnetic or ferromagnetic behavior depending on the value of spin-coupling. It was shown that the number, composition, and distribution of paramagnetic centers excited in the mono- and bipolymer photovoltaic systems are determined by their structure, morphology, as well as by the density and energy of the initiating light photons.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Resultsmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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“…The left-situated extremum is recorded around the energy of the bandgap of the polymer backbone, Δ E g = E HOMO – E LUMO = 1.80 eV, whereas the other extremum appears at the higher photon energies. A similar effect was also manifested when studying charge carriers photoinitiated in different photovoltaic composites ,,, and was explained to arise due to the interaction of captured charge carriers with the light photons and neighboring paramagnetic centers. Replacing the PC 61 BM acceptor with the ITIC-M one in the composite leads to a significant, more than an order of magnitude, increase in the number of all spin charge carriers.…”

Section: Resultsmentioning

confidence: 54%

“…This evidences that this process is carried out in the composites within the framework of the above-mentioned approach. It should be noted that the appearance occurred only after some time in the dependencies shown in Figure of the bell-like component as in the case of other polymer:fullerene composites. , Assuming the presumption of formation of an equal quantity of positively and negatively charged carriers upon excitons’ dissociation, some reasons for such effect can be proposed. Dissociation of some diamagnetic bipolarons into polaron pairs − and/or formation in composites of pairs of localized oppositely charged polarons P loc +• ↔ P loc –• with equal energy and g -factors are possible .…”

Section: Resultsmentioning

confidence: 94%

“…It should be noted that the appearance occurred only after some time in the dependencies shown in Figure 10 of the bell-like component as in the case of other polymer:fullerene composites. 33,52 Assuming the presumption of formation of an equal quantity of positively and negatively charged carriers upon excitons' dissociation, some reasons for such effect can be proposed. Dissociation of some diamagnetic bipolarons into polaron pairs 61−63 can also provoke such dependence.…”

Section: Lepr Spectral Composition and Magneticmentioning

confidence: 99%

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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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Effects of small-molecule-doping on spin-assisted processes in P3DDT:PC61BM photovoltaics

et al. 2020

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Light-induced EPR study of spin-assisted charge transport in PFOT:PC61BM composite

Cited by 4 publications

References 23 publications

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

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

Effects of small-molecule-doping on spin-assisted processes in P3DDT:PC61BM photovoltaics

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