Physical mechanisms on FRET and ICT for efficient Y6:PM6 as bulk heterojunction active layers

Organic solar cells (OSCs) have emerged as a promising new energy technology because of their advantages of efficient light harvesting, comprehensive material sources, and flexible and translucent devices. In this study, fluorescence resonance energy transfer (FRET) and intermolecular charge transfer (ICT) in the donor-acceptor system for efficient OSCs of the Y6:PM6 heterostructure are investigated with ultrafast pump-probe transient absorption spectroscopy, time-resolved fluorescence spectroscopy, steady absorption, and fluorescence spectroscopy, which is significantly supported by theoretical results. The physical mechanisms of FRET and ICT in the donor-acceptor system for efficient OSCs of the Y6:PM6 heterostructure are investigated theoretically and experimentally. FRET can decrease the recombination of electron-hole in the donor's fluorescence and enhance the acceptor's fluorescence. Our study contributes to a better understanding of FRET and ICT and provides valuable references for the rational design of FRET- and ICT-based OSCs.