Prolonged-Nucleation Strategy via an Asymmetric Brominated Acceptor Enables > 20% Efficiency in Five Different...

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 × 10¹⁵ 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 (T₉₀ = 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.