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The hole‐transporting material (HTM), poly (3,4‐ethylene dioxythiophene) poly(styrene sulfonate) (PEDOT : PSS), is the most widely used material in the realization of high‐efficiency organic solar cells (OSCs). However, the stability of PEDOT : PSS‐based OSCs is quite poor, arising from its strong acidity and hygroscopicity. In addition, PEDOT : PSS has an absorption in the infrared region and high highest occupied molecular orbital (HOMO) energy level, thus limiting the enhancement of short‐circuit current density (Jsc) and open‐circuit voltage (Voc), respectively. Herein, two asymmetric self‐assembled molecules (SAMs), namely BrCz and BrBACz, were designed and synthesized as HTM in binary OSCs based on the well‐known system of PM6 : Y6, PM6 : eC9, PM6 : L8‐BO, and D18 : eC9. Compared with BrCz, BrBACz shows larger dipole moment, deeper work function and lower surface energy. Moreover, BrBACz not only enhances photon harvesting in the active layer, but also minimizes voltage losses as well as improves interface charge extraction/ transport. Consequently, the PM6 : eC9‐based binary OSC using BrBACz as HTM exhibits a champion efficiency of 19.70 % with a remarkable Jsc of 29.20 mA cm−2 and a Voc of 0.856 V, which is a record efficiency for binary OSCs so far. In addition, the unencapsulated device maintains 95.0 % of its original efficiency after 1,000 hours of storage at air ambient, indicating excellent long‐term stability. [ABSTRACT FROM AUTHOR]

Substantial efforts of A–DA′D–A type non‐fullerene acceptors (NFAs) molecular design have impelled power conversion efficiency (PCE) of single junction organic solar cells (OSCs) to exceed 19%. Asymmetric geometry strategy, selenium‐substitution, and end‐group engineering are proven to be effective modification methods. Here, two novel selenium substitution asymmetric NFAs, AsymSSe‐2F, and AsymSSe‐2Cl, are synthesized to investigate the synergistic modification effects on device performance compared with symmetric Y6. When blending AsymSSe‐2F with the wide‐bandgap and high crystallinity polymer D18, a remarkable PCE of 18.31% is yielded, and an excellent fill factor of 79.46% is achieved, which is attributed to the broadened absorption, enhanced π–π stacking, balanced carrier mobilities, and fine phase‐separation morphology. Notably, among the reported selenium‐substituted asymmetric NFAs based OSCs, especially combined with the seldom‐reported D18, this PCE is top‐ranked in binary bulk heterojunction organic solar cells. This work indicates that the combined modification of asymmetric geometry and selenium substitution in NFAs is a promising strategy for fabricating high performance OSCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two non-fullerene donors with A-π-A'-π-A type structures designed and synthesised. • The structures contain 3-hexylrhodanine and 2-butyl cyanoacetate end groups. • The introduction of DB-1/2 achieved dual FRET in PM6:Y6 system for the first time. • The excessive self-aggregation of Y6 was broken in ternary solar cells. • The ternary organic solar cells achieve high J SC of 28.0 mA cm−2. 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 (J SC). 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 J SC 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 J SC and FF of OSCs. [ABSTRACT FROM AUTHOR]