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. Controlling long-range, directional fibrillar morphology is important for organic solar cells (OSC). Here, the authors show that cobalt phosphosulfide nanocrystals can template film formation in OSCs, improving charge generation and transport, and achieving a power conversion efficiency of 21.0%.