Prolonged‐Nucleation Strategy via an Asymmetric Brominated Acceptor Enables > 20% Efficiency in Five Different Organic Solar Cells

Abstract

Abstract Despite efficient charge transfer and molecular stacking in BTP‐core acceptors, overly rapid nucleation often causes growth of unfavorable donor/acceptor (D/A) fibrillar networks and metastable morphologies, limiting device efficiency and stability. Herein, an asymmetric acceptor T10, featuring a brominated acenaphtho‐quinoxaline central core, is developed as a nucleation‐regulating ternary component. The extended 2D core promotes multi‐site molecular stacking, prolonging nucleation time to 280 ms—twice that of classical eC9‐4F. The strong non‐covalent interactions between asymmetric T10 and PM6/eC9‐4F suppress excessive D/A mixing while forming a tailored fibrillar network. Thus, the ternary device demonstrates an extended carrier lifetime (3.224 µs) and a reduced defect density (1.37 × 10 15 cm −3 ), resulting in low energy disorder (21.82 meV). These effects enhance the open‐circuit voltage (0.873 V) and fill factor (80.68%), leading to a high efficiency of 19.91%. Additionally, the ternary device provides a superior photostability ( T 90 = 1609 h) compared with the two binary systems (127 and 726 h). More importantly, the T10‐mediated prolonged nucleation has been successfully validated in five BTP‐based acceptors, achieving PCEs of 20.07% (D18:eC9:T10), 20.40% (D18:BO‐4Cl:T10), 20.47% (D18:L8‐BO‐X:T10), 20.52% (D18:L8‐BO:T10), and 20.67% (D18:eC9‐4F:T10, certified 20.1%). This study demonstrates a molecularly engineered strategy with broad universality for extending nucleation kinetics in acceptor.