Multifrequency EPR analysis of the positive polaron in I2-doped poly(3-hexylthiophene) and in poly[2-methoxy-5-(3,7-dimethyloctyloxy)]-1,4-phenylenevinylene

Aguirre, Aránzazu; Gast, P.; Orlinskiĭ, S. B.; Akimoto, Ikuko; Groenen, E. J. J.; Mkami, Hassane El; Goovaerts, E.; Doorslaer, Sabine Van

doi:10.1039/b811419f

Cited by 76 publications

(134 citation statements)

References 39 publications

(62 reference statements)

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“…1(a)] are obtained by assuming two resonances with g ¼ 2:0028ð3Þ, a narrow pseudo-Voigtian line shape (FWHM ¼ 0:6ð1Þ mT) and a wider Gaussian component (1:5ð1Þ mT), with identical doubly integrated intensities [14]. The linewidths and g values agree with earlier EDMR and light-induced EPR measurements on polarons in PPV [12,15,16]. The g value excludes the possibility that PCBM anions (g ¼ 1:9995) are making a significant contribution to the spectrum [12].…”

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confidence: 74%

Bipolaron Formation in Organic Solar Cells Observed by Pulsed Electrically Detected Magnetic Resonance

et al. 2010

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We report the observation of a spin-dependent dark transport current, exhibiting spin coherence at room temperature, in a -conjugated polymer-fullerene blend using pulsed electrically detected magnetic resonance. The resonance at g ¼ 2:0028ð3Þ is due to polarons in the polymer, and exhibits spin locking at high microwave fields. The presence of an excess of fullerene, and the operating voltage (1 V) used, suppresses negative polaron formation in the polymer. It is concluded that spin-dependent transport is due to the formation of positive bipolarons. DOI: 10.1103/PhysRevLett.105.176601 PACS numbers: 72.80. Le, 71.38.Mx, 72.25.Rb, 76.30.Mi Organic semiconductors provide a range of commercial optoelectronic display devices, and show great promise in the field of photovoltaics (PV) [1][2][3][4] if improved efficiency, combined with low cost and ease of production, can be achieved. In addition, the weak spin-orbit coupling of organic semiconductors is attractive for carrier spin transport and manipulation, and is driving efforts to develop spintronic devices [5]. All these applications depend upon detailed knowledge of the relevant transport processes, in particular, those influenced by spin selection rules. The observation of large magnetoresistance (MR) has, for example, attracted a range of explanations [6][7][8][9], but aspects of the proposed mechanisms remain controversial [10].Conduction in disordered organic semiconductors is dominated by hopping of charge carriers between localized states. Because of strong electron-phonon coupling the carriers are polarons. Oppositely charged polarons can form excitons and eventually recombine; the process normally depends on the spin state of the coupled pair immediately prior to exciton formation. In addition, the strong coupling between carriers and the environment can markedly reduce the energy cost of doubly occupying states. Two like-charge polarons can form a bipolaron, the correlation energy between the pair and the lattice deformation lowering the formation energy [11]. However, the on-site exchange requires that the final state is a spin singlet, and bipolaron formation will be ''spin-blocked'' if two polarons have the same spin component along the common axis of quantization [8].Organic PV devices have advanced dramatically with the development of bulk heterojunction materials [2][3][4], which comprise a -conjugated polymer blended with an electron acceptor such as a fullerene derivative. The two phase-separated components give interpenetrating networks with vastly increased interfacial regions [3]. The PVeffect is due to photoexcitation of the polymer, followed by highly efficient electron transfer to the fullerene phase. Positive polarons (P þ ) are transported through the polymer matrix, negative polarons through the fullerene phase, efficiently suppressing carrier loss by P þ P À recombination. However, unipolar transport to the electrodes may be influenced by bipolaron formation. Gaining insight into this process, which affects charge carrier collection...

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confidence: 74%

Bipolaron Formation in Organic Solar Cells Observed by Pulsed Electrically Detected Magnetic Resonance

et al. 2010

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“…21 Note, that the g P iso value of the latter measured more accurately at W-band (94 GHz) EPR is equal to 2.00187. 26 These parameters were appeared to become weakly temperature dependent than those of the P3HT/PCBM composite. 21 As in case of other polymer/fullerene systems, 20,21 LEPR spectra of the P3HT/bis-PCBM bulk heterojunctions consists of two Lorentzian contributions of mobile polarons and bis-methanofullerene anion radicals in quasi-pairs P…”

Section: A Spectral Composition and G-factormentioning

confidence: 96%

“…This was confirmed later at millimeter waveband LEPR study of the P3HT/PCBM composite. Thus, it was shown that the spin of polarons photoinduced in the P3HT chains is also characterized by rhombic symmetry originating anisotropic g-factor with g xx = 2.0028, g yy = 2.0019, g zz = 2.0009 at W-band (94 GHz) EPR 26 and g xx = 2.00380, g yy = 2.00230, g zz = 2.00110 at D-band (130 GHz) EPR. 29 Spin distribution in the mC −• 61 anion radical embedded into P3HT matrix is also characterized by rhombic symmetry that leads to respective anisotropy of its g-factor with g xx = 2.00058, g yy = 2.00045, g zz = 1.99845.…”

Section: A Spectral Composition and G-factormentioning

confidence: 99%

Light-induced EPR study of charge transfer in P3HT/bis-PCBM bulk heterojunctions

Krinichnyi

Yudanova

2011

AIP Advances

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Radical pairs, polarons and fullerene anion radicals photoinduced by photons with energy of 1.98 – 2.73 eV in bulk heterojunctions formed by poly(3-hexylthiophene) (P3HT) with bis(1-[3-(methoxycarbonyl)propyl]-1-phenyl)-[6.6]C62 (bis-PCBM) fullerene derivative have been studied by direct light-induced EPR (LEPR) method in a wide temperature range. A part of photoinduced polarons are pinned in trap sites which number and depth are governed by an ordering of the polymer/fullerene system and energy of initiating photons. It was shown that dynamics and recombination of mobile polarons and counter fullerene anion radicals are governed by their exchange- and multi-trap assisted diffusion. Relaxation and dynamics parameters of both the charge carriers were determined separately by the steady-state saturation method. These parameters are governed by structure and conformation of the carriers’ microenvironment as well as by the energy of irradiating photons. Longitudinal diffusion of polarons was shown to depend on lattice phonons of crystalline domains embedded into an amorphous polymer matrix. The energy barrier required for polaron interchain hopping is higher than that its intrachain diffusion. Pseudorotation of fullerene derivatives in a polymer matrix was shown to follow the activation Pike model.

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“…Because of the higher resolution at W-band microwave frequencies, the LI-EPR spectrum now reveals distinct features. For comparison, the previously reported 32 W-band ESE-detected EPR blend (signal marked with asterisk in Fig. 6), together with a second feature at a higher g value (signal marked with # centered at g = 2.0045 in Fig.…”

Section: Polaron Detection By Electron Paramagnetic Resonancementioning

confidence: 99%

Charge transfer in the weak driving force limit in blends of MDMO-PPV and dithienylthiazolo[5,4-d]thiazoles towards organic photovoltaics with high VOC

Nevil

Ling

Mierloo

et al. 2012

Phys. Chem. Chem. Phys.

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Photoluminescence quenching together with polaron detection by electron paramagnetic resonance and photoinduced absorption (PIA) demonstrate an increasing charge transfer efficiency when the DTTzTz substituents are varied from thien-2-yl to 4-trifluoromethylphenyl and 4-cyanophenyl groups, correlating well with the increasing acceptor strength in this series of molecules. In line with this observation, there is a decrease in the effective optical bandgap relative to pure MDMO-PPV that becomes more pronounced along this series of acceptor compounds, reaching 0.12 eV in the blend with 4-CN-Ph-DTTzTz. Intermolecular interactions between the blend components lead to lower energy transitions which are found to contribute significantly to the device external quantum efficiency. The high V OC reached in devices based on MDMO-PPV:4-CN-Ph-DTTzTz blends meets the expectations for such a donor:acceptor combination. However, thermal activation of charge carrier recombination occurs because of the weak driving force for charge transfer, as shown by time-dependent PIA measurements, and this is suggested as a cause for the observed low photovoltaic performance.

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Multifrequency EPR analysis of the positive polaron in I2-doped poly(3-hexylthiophene) and in poly[2-methoxy-5-(3,7-dimethyloctyloxy)]-1,4-phenylenevinylene

Cited by 76 publications

References 39 publications

Bipolaron Formation in Organic Solar Cells Observed by Pulsed Electrically Detected Magnetic Resonance

Bipolaron Formation in Organic Solar Cells Observed by Pulsed Electrically Detected Magnetic Resonance

Light-induced EPR study of charge transfer in P3HT/bis-PCBM bulk heterojunctions

Charge transfer in the weak driving force limit in blends of MDMO-PPV and dithienylthiazolo[5,4-d]thiazoles towards organic photovoltaics with high VOC

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