Optical detection of ESR spectra of short-lived ion-radical pairs produced in solution by ionizing radiation

Molin, Yu. N.; Анисимов, О. А.; Grigoryants, Vladimir M.; Molchanov, V. K.; Salikhov, K. M.

doi:10.1021/j100451a023

Cited by 65 publications

(20 citation statements)

References 2 publications

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“…This effect was previously observed for radical pairs in biological systems. 146 In our case the appearance of spin locking can be rationalized as follows.…”

Section: Pedmr On Meh-ppv:pcbm Solar Cellsmentioning

confidence: 84%

Pulsed electrically detected magnetic resonance for thin film silicon and organic solar cells

Schnegg

Behrends

Fehr

et al. 2012

Phys. Chem. Chem. Phys.

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In thin film solar cells based on non-crystalline thin film silicon or organic semiconductors structural disorder leads to localized states that induce device limiting charge recombination and trapping. Both processes frequently involve paramagnetic states and become spin-dependent. In the present perspectives article we report on advanced pulsed electrically detected magnetic resonance (pEDMR) experiments for the study of spin dependent transport processes in fully processed thin film solar cells. We reflect on recent advances in pEDMR spectroscopy and demonstrate its capabilities on two different state of the art thin film solar cell concepts based on microcrystalline silicon and organic MEH-PPV:PCBM blends, recently studied at HZB. Benefiting from the increased capabilities of novel pEDMR detection schemes we were able to ascertain spin-dependent transport processes and microscopically identify paramagnetic states and their role in the charge collection mechanism of solar cells.

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“…This effect was previously observed for radical pairs in biological systems. 146 In our case the appearance of spin locking can be rationalized as follows.…”

Section: Pedmr On Meh-ppv:pcbm Solar Cellsmentioning

confidence: 84%

Pulsed electrically detected magnetic resonance for thin film silicon and organic solar cells

Schnegg

Behrends

Fehr

et al. 2012

Phys. Chem. Chem. Phys.

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“…This is an indication of coupled spin pairs, where the resonance spectra of each member overlap. When B 1 is sufficiently high to simultaneously excite the EPR of both members of the pair, spin locking occurs [18]. The EDMR spectrum is often assumed to be due to the formation of S ¼ 1=2 spin pairs as part of a transport process in which a rate constant is markedly higher for the singlet configuration, compared to the triplet states.…”

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confidence: 99%

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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“…A small frequency contribution at ν ≈ 47 MHz is observed in the FFT spectrum, which is due to the spin-locking frequency sl CE = 2 CE . This occurs under experimental conditions that allow for a simultaneous manipulation of both spins of a weakly coupled spin pair [38,57] paramagnetic centers in the triplet S = 1 state, which influence the photocurrent. However, the measured frequencies differ from the expected pure S = 1 frequency at ν TE = 33.54 MHz.…”

Section: B Electrical Detection Of Rabi Nutationsmentioning

confidence: 99%

Triplet excitons as sensitive spin probes for structure analysis of extended defects in microcrystalline silicon

et al. 2016

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Electrically detected magnetic resonance (EDMR) spectroscopy is employed to study the influence of triplet excitons on the photocurrent in state-of-the-art microcrystalline silicon thin-film solar cells. These triplet excitons are used as sensitive spin probes for the investigation of their electronic and nuclear environment in this mixedphase material. According to low-temperature EDMR results obtained from solar cells with different 29 Si isotope concentrations between 0.01% and 50%, the triplet excitons reside at extended defects in the crystallites of microcrystalline silicon that give rise to shallow states in the silicon band gap. The excitons possess a rather delocalized wave function, couple to electron spins in conduction band tail states nearby, and take part in a spin-dependent recombination process. Our study shows that extended defects such as grain boundaries or stacking faults in the crystalline part of the material act as charge carrier traps that can influence the material conductivity.

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Optical detection of ESR spectra of short-lived ion-radical pairs produced in solution by ionizing radiation

Cited by 65 publications

References 2 publications

Pulsed electrically detected magnetic resonance for thin film silicon and organic solar cells

Pulsed electrically detected magnetic resonance for thin film silicon and organic solar cells

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

Triplet excitons as sensitive spin probes for structure analysis of extended defects in microcrystalline silicon

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