  We offer a theoretical perspective on simulation and engineering of
polaritonic conical-intersection-driven singlet-fission (SF) materials. Using
rubrene as an example and applying the numerically accurate Davydov-Ansatz
methodology, we derive dynamic and spectroscopic responses of the system and
demonstrate key mechanisms capable of SF manipulation, viz. cavity-induced
enhancement/weakening/suppression of SF, population localization on the singlet
state via engineering of the cavity-mode excitation, polaron/polariton
decoupling, collective enhancement of SF. We outline unsolved problems and
challenges in the field, and share our views on the development of the future
lines of research. We emphasize the significance of careful modeling of
cascades of polaritonic conical intersections in high excitation manifolds and
envisage that collective geometric phase effects may remarkably affect the SF
dynamics and yield. We argue that microscopic interpretation of the main
regulatory mechanisms of the polaritonic conical-intersection-driven SF can
substantially deepen our understanding of this process, thereby providing novel
ideas and solutions for improving conversion efficiency in photovoltaics.
