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Charge Transfer Processes in OPV Materials as Revealed by EPR Spectroscopy
Author(s) -
Niklas Jens,
Poluektov Oleg G.
Publication year - 2017
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201602226
Subject(s) - electron paramagnetic resonance , polaron , materials science , delocalized electron , chemical physics , spectroscopy , fullerene , hyperfine structure , paramagnetism , photochemistry , pulsed epr , organic solar cell , polymer solar cell , charge carrier , photoinduced charge separation , polymer , nuclear magnetic resonance , optoelectronics , chemistry , atomic physics , electron , organic chemistry , condensed matter physics , physics , photocatalysis , magnetic resonance imaging , composite material , quantum mechanics , radiology , medicine , spin echo , artificial photosynthesis , catalysis
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.