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

Yoriko Sonoda,Masanobu Wakasa,Tomoaki Yago,Ryuzi Katoh

doi:10.1038/s42004-018-0008-0

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.

Highlights

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
Since 2000, interest in singlet fission has been greatly stimulated by the possibility that it might be used to increase the maximum efficiency of solar cells[9] to more than 40%, greater than the value of Shockley–Queisser limit (32%)[10] for single-junction devices
In the case of a correlated triplet-exciton pair (TP) in which there was a distinct exchange interaction, we recently reported that singlet fission from an organic crystal of 1,6-diphenyl-1,3,5hexatriene (DPH) showed clear magnetic field effects (MFEs) at magnetic field strengths of 0–5 T38

Summary

Introduction

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. In the absence of a magnetic field, the spin states in separated TPs are defined based on the dipole–dipole coupling in a triplet exciton. The MFE in low magnetic fields of < 0.15 T is anisotropic and is sensitive to the structure of the separated TPs. Here we study MFEs on the singlet fission of DPH and fluorinated DPH crystals at magnetic field strengths < 0.15 T.

Results

Conclusion