Recent Advances in Singlet Fission

TLDR

Efficient singlet‑fission materials are largely acenes, but broader structural diversity is needed. The review surveys recent progress in understanding singlet fission, a spin‑allowed process that splits one singlet into two triplets. It outlines first‑principles‑based design rules for singlet‑fission materials and presents initial implementation examples. Singlet fission occurs in various solids on 80 fs–25 ps timescales, yielding up to 200 % triplet production, and devices achieve >100 % external quantum efficiency.

Abstract

A survey is provided of recent progress in the understanding of singlet fission, a spin-allowed process in which a singlet excited molecule shares its energy with a ground-state neighbor to produce two triplet excited molecules. It has been observed to occur in single-crystal, polycrystalline, and amorphous solids, on timescales from 80 fs to 25 ps, producing triplet yields as high as 200%. Photovoltaic devices using the effect have shown external quantum efficiencies in excess of 100%. Almost all the efficient materials are alternant hydrocarbons of the acene series or their simple derivatives, and it is argued that a wider structural variety would be desirable. The current state of the development of molecular structure design rules, based on first-principles theoretical considerations, is described along with initial examples of implementation.