Donor- or acceptor-type 9,9'-bifluorenylidene derivatives for attaining singlet fission character in organic photovoltaics

Abstract

Donor-type and acceptor-type 9,9¤-bifluorenylidene derivatives, MOBF and CNBF, were synthesized. Suitable energy levels on the excited states of the compounds for singlet fission were revealed by density functional theory calculation. Thermal and optoelectronic properties of the compounds were investigated, and the OPV devices with the donor-type MOBF and the acceptor-type CNBF were fabricated. MOBF showed large dependence of photocurrent on magnetic field, suggesting the singlet fission behavior in the OPV device. On the other hand, CNBF did not show any magnetic field dependence of photocurrent, probably because of poor morphology.