Triplet pair dynamics of singlet fission in orthorhombic polycrystalline powder of rubrene as revealed by magnetoluminescence

Singlet fission, which may increase the energy conversion efficiency of solar cells, proceeds via multiple spin levels of a triplet pair. To clarify the spin-related elementary processes of the triplet pair, we measured the magnetoluminescence effect of the fluorescence of rubrene, in the form of orthorhombic polycrystalline powder, in the range of ±300 mT at room temperature. Model simulations using the density matrix method were performed to elucidate how the features of the magnetoluminescence effect depend on the triplet pair dynamics. Simulations of the observed field dependence of the magnetoluminescence effect revealed an anisotropy of 1:100 for the two-dimensional hopping of triplet excitons forming a triplet pair in the ab plane, for which the exchange interaction depends on the separation distance between the two triplet excitons. The effective lifetime of the spin-correlated triplet pair responsible for the magnetoluminescence effect is estimated to be 2.2 ns.