Resolving Ternary Morphology for High-Performance Thickness-Insensitive Organic Solar Cells.

High-performance organic solar cells (OSCs) suffer from low active layer thickness tolerance, which is incompatible with large-scale printing technology originally envisioned for low-cost module manufacturing. Herein, by incorporating a large amount of small-molecule donor BTR-Cl into the prototypical PM6/Y6 blend film, we fabricated efficient ternary devices with a photoconversion efficiency of 17.7% at an active layer thickness of 300 nm, among the best-performing thick-film devices reported so far. To elucidate its morphological origin, we deuterated both Y6 and BTR-Cl to resolve their morphology in ternary blend films separately via grazing-incidence small-angle neutron scattering (GISANS). We observed enhanced short-range aggregation of both Y6 and BTR-Cl within the intermixed domains of the ternary blend film induced by the accelerated molecular assembly process. Those aggregates act as effective bridges between crystalline domains to improve connectivity in both donor and acceptor phases, resulting in enhanced carrier mobility, suppressed space charge accumulation, and consequently significantly improved thickness tolerance in ternary devices. Our work demonstrates the effectiveness of combined targeted deuteration and GISANS to resolve the complicated structures within multicomponent OSC active layers and highlights the critical role of amorphous nanomorphology in carrier transport connectivity and, consequently, the thickness tolerance of high-performance OSCs.