Dual Förster resonance energy transfer effects enables high photocurrent density and high fill factor in ternary organic solar cells

Organic solar cells (OSCs) have aroused widespread concerns in green energy and wearable electronics. One of the most powerful way to achieve high efficient OSCs is maximizing fill factor (FF) and short-circuit current density (JSC). Herein, two A-π-A'-π-A type conjugated molecules bearing different electron-deficient end groups, DB-1 and DB-2, were designed and synthesized as donor-typed third components in the well-known PM6:Y6 host system. The photoluminescence and ultrafast transient absorption spectra clearly demonstrated that dual Förster resonance energy transfer (FRET) effects were well established for the first time in the PM6:Y6-based ternary OSCs. Furthermore, the introduction of DB-1 and DB-2 could effectively prevent the excessive self-aggregation of Y6, resulting in the optimal phase separations in the ternary films. Thus, the ternary OSCs based on PM6:DB-1:Y6 and PM6:DB-2:Y6 both achieved excellent JSC of ∼28.0 mA cm−2 and high FF ∼0.780, which are significantly higher than those of the binary devices. Consequently, rational molecular design and dual FRET effects provide a new and effective method to simultaneously improve the JSC and FF of OSCs.