Kinetically templated fibrillar self-assembly via two-dimensional nanocrystals enables 21% efficient organic solar cells.

The performance of organic solar cells (OSCs) is critically governed by the fibrillar organization of bulk-heterojunction active layers, yet controlling long-range, directional fibrillar morphology under nonequilibrium processing remains challenging. Here we report that two-dimensional cobalt phosphosulfide (CoPS3) nanocrystals act as kinetic templates that reprogram molecular self-assembly during film formation. Through collective electronic interactions with conjugated polymer donors and small-molecule acceptors, CoPS3 modulates molecular densification and phase separation pathways, enabling refined, long-range fibrillar networks without increasing crystallinity. The resulting morphology enhances exciton dissociation and charge transport, and inhibits recombination, delivering a power conversion efficiency of 21.0%. This templating strategy is effective across multiple OSC systems, simultaneously improving efficiency and storage stability, offering a promising route for kinetic morphology control in organic optoelectronics.