Molecularly matched trace dopant enables dual-channel modulation for 19.98%-Efficiency organic solar cells

Organic solar cells (OSCs) achieve high photovoltaic output largely by regulating the nanoscale morphological structure of their photoactive layers. Trace doping has emerged as a promising strategy to simultaneously optimize morphological characteristics and charge dynamics; however, conventional p- or n-type dopants are often constrained by limited molecular diversity, complex screening processes, and the risk of inducing undesirable recombination pathways. Herein, we report a multifunctional trace dopant, a benzotriazole derivative (1-HB), featuring a molecular skeleton that is highly compatible with the acceptor material L8-BO. At an ultralow concentration (0.05 mg mL⁻¹), 1-HB enables precise morphology regulation in PM6:L8-BO film. Comprehensive characterization reveals that 1-HB synergistically modulates crystallization dynamic behavior of both donor (PM6) and acceptor (L8-BO) phases via strong intermolecular interactions, leading to enhanced molecular packing, increased structural order, improved crystallinity and coherence length, and the construction of an optimal vertical phase separation gradient that facilitates efficient charge transport. Femtosecond transient absorption spectroscopy further demonstrates that 1-HB accelerates charge separation, reducing the hole transfer lifetime τ₁ from 2.047 ps to 0.858 ps, while simultaneously optimizing charge separation pathways by decreasing the contribution of slower processes from 26.4% to 19.5%. These combined effects facilitate ultrafast exciton dissociation and suppress bimolecular as well as trap-mediated recombination, which in turn effectively reduces non-radiative energy losses. Consequently, the optimized devices deliver a best power conversion efficiency (PCE)-19.98%, a remarkable improvement over the 18.41% of control devices, along with simultaneous enhancements in fill factor (FF), open-circuit voltage (V_OC) and short-circuit current density (J_SC). This acceptor-skeleton-matched trace doping strategy establishes a general molecular design paradigm for high-efficiency, low-dosage active layer dopants, offering substantial promise for advancing high-performance organic photovoltaics. © 2026 The Authors.