Conjugated Polymer Singlet Fission Material with High Triplet Energy and Long Multiexciton Lifetime via Donor‐π‐Acceptor Strategy

Abstract The progress in singlet fission (SF)‐based devices remains basically stagnant due to the limited scope of practical SF materials. Donor–acceptor conjugated polymers hold particular appeal for SF and photovoltaic applications, yet such type SF materials remain largely unexplored, and the previously reported systems are usually beset by low triplet energy and short multiexciton (ME) lifetime impeding their practical applications. In this work, a donor‐π‐acceptor design strategy is presented and successfully develop a new practical polymer SF system. The comprehensive spectroscopic analyses clearly validate that such a molecular design enables the polymer system to hold suitable triplet energy of 1.0–1.1 eV and long ME lifetime of ≈600 ps and implement ultrafast and quantitative ME generation in both dilute solution and solid aggregates. These merits, along with the good processability and excellent stability, make such polymer systems particularly well‐suited for SF‐based light harvesting applications. These results highlight the practical polymer SF system and feasible design guidelines, which can not only pave the way to the discovery of rare polymer SF materials but also lay the foundation for the further implementation of highly efficient SF‐based photovoltaic devices.