Excitons and polaritons in singlet fission materials: Photophysics, photochemistry, and optoelectronics

Organic (opto)electronic materials have been explored in a variety of applications in electronics and photonics, driven by several advantages over traditional silicon technology, including low-cost processing, fabrication of large-area flexible devices, and widely tunable properties through functionalization of the molecules. Over the past decade, remarkable progress has been achieved in understanding physical mechanisms and in developing guidelines for material design, which have boosted the performance of organic devices. However, further improvements in device performance are desirable, and challenges related to (photo)stability of organic devices need addressing. One of the major thrusts in developing new organic materials and device concepts has focused on materials exhibiting singlet fission, which is a charge-carrier multiplication process that could enable, for example, enhanced power-conversion efficiencies in solar cells. Nevertheless, fundamental questions pertaining to exciton physics in singlet fission materials, and how it can be manipulated by material design and external parameters, remain. Strong exciton–photon coupling that occurs when an organic film is placed in a microcavity, enabling formation of a light–matter hybrid state (polariton), presents a largely unexplored opportunity to control photophysics, photochemistry, and optoelectronic characteristics in singlet fission materials and devices using polaritons. In this article, we review the key requirements for singlet fission materials and promising advances toward controlling their properties using polaritons. Graphical abstract