Influence of Photogeneration Frequency on the Transport of Spin Charge Carriers in the Copolymer–Methanofullerene Composite: EPR Study
The photovoltaic composite formed by narrow-gap copolymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(bithiophene)] and methanofullerene [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) has been studied in a wide energy range of generating photons, 1.32–3.14 eV at T = 77 K, by the light-induced electron paramagnetic resonance. It has been shown that some polarons are captured by spin traps formed in the copolymer matrix, and the concentration and depth of such traps are determined by the photon energy. The recombination kinetics of polarons and fullerene radical anions after turning off the light can be described in the framework of a second-order bimolecular process. The formation of spin traps in the copolymer matrix and the exchange interaction between different spin packets cause the extreme sensitivity of magnetic resonance and electronic parameters of charge carriers to the number and energy of generating photons.
Keywords:bulk heterojunction photoinduced EPR spin relaxation charge recombination charge transfer polaron methanofullerene exciton dissociation
This work was carried out within the State assignment no. 0089-2014-0036 and was supported by the Russian Foundation for Basic Research, project no. 18-29-20011.
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