Structure and dynamics of triplet-exciton pairs generated from singlet fission studied via magnetic field effects

Abstract

Singlet fission is the conversion of a singlet exciton to a pair of triplet excitons followed by a diffusion process to form two free triplet excitons. The quantum yield of singlet fission per photon can exceed 100%. Singlet fission is thus an attractive way to enhance solar-cell performance. However, singlet fission events are not well characterized. In particular, the structure and diffusion pathways of triplet-exciton pairs, which strongly affect the efficiency of the singlet fission event, are unclear. Here we study the magnetic field effects (MFEs) on the singlet fission of diphenylhexatriene (DPH) and fluorinated DPHs crystals. Their fluorescence intensities show clear MFEs and the shape of the MFE curve depends on the crystal structure. Analysis of MFEs with the stochastic Liouville equation reproduces the MFE curve well. This use of MFEs allows one to determine the structure and diffusion pathways of triplet-exciton pairs, and to predict the efficiency of singlet fission events.