Simultaneously Broaden Absorption and Minimize Energy Loss via a Guest Asymmetric Acceptor for 20.7% Efficiency Ternary Organic Solar Cells

ABSTRACT Minimizing non‐radiative recombination energy loss (Δ E nr ) while broadening the absorption spectrum remains a key challenge for achieving high‐performance ternary organic solar cells (OSCs). Here, we introduce the asymmetric narrow bandgap acceptor SSe‐4F as the guest component into the donor and acceptor layers to prepare ternary pseudo‐planar heterojunction (PPHJ) OSCs. Thus, an extended photon trapping range as well as an improved response value of spectral absorption are realized. Moreover, the larger dipole moment of SSe‐4F facilitates the enhancement of intermolecular forces and the optimization of molecular stacking. Meanwhile, the introduction of SSe‐4F prolongs the crystallization period of PM6 and L8‐BO, respectively, and promotes the formation of distinct vertical phase separation morphologies. Hence, the energy disorder and Δ E nr of PM6:SSe‐4F/L8‐BO:SSe‐4F‐based device is reduced. In addition, the exciton lifetime and the stability of the ternary PPHJ device are improved. Consequently, the PM6:SSe‐4F/L8‐BO:SSe‐4F (1:0.05/1.1:0.1)‐based OSCs achieve a champion power conversion efficiency of 20.68% without open‐circuit voltage loss, and exhibit great photostability with a T 80 lifetime of 1050 h. This work indicates an emerging approach for fabricating high‐performance stabilized ternary OSCs which simultaneously decreases bandgap and energy loss.