EPR Study of Photogeneration of Spin Charge Carriers in Fullerene-Free Polymer Composites PBDB-T : IT-M

The paper presents the results of an EPR study of a new organic photovoltaic composite with a nonfullerene acceptor PBDB-T : IT-M. The parameters of the EPR spectra of all photogenerated spin charge carriers, both trapped and mobile, have been determined, which are in good agreement with previously reported data. The dependences of the spin concentration of all trapped and mobile charge carriers on the photon energy demonstrate an extreme increase in the region of 2.37 eV, which coincides with the band gap of the PBDB-T : IT-M polymer composite. The introduction of 2,5-diphenyloxazole (PPO) as a photoactivator into the system of trace additives improves the composite morphology as a result of more intense π–π interaction between the components, which enhances the exchange interaction between them and stabilizes the amount of spin charge carriers, mainly localized in the energy traps of the polymer matrix. The exchange interaction between polymers and diphenyloxazole in the composite leads to a twofold increase in the number of spins in the energy region close to the band gap of the composite.