Trade‐Off Break between the Crystallinity and Phase Separation of Donor/Acceptor via a General Two‐Dimensional Transition‐Metal Phosphorus Trichalcogenides Nanoparticle Dopant Concept for Efficient and Stable All‐Polymer Solar Cells

All‐polymer solar cells (all‐PSCs) demonstrate splendid advantages of thermal and mechanical stability. Nevertheless, the rock‐ribbed trade‐off between the crystallinity and phase separation scale of donor/acceptor (D/A) hinder the power conversion efficiency (PCE) improvement of all‐PSCs. Here, a novel two‐dimensional transition‐metal phosphorus trichalcogenides (TMPTCs) namely Cd 0.85 PS 3 Li 0.3 is intelligently designed and synthesized, and firstly employed as a nanoparticle dopant for PBDB‐T:N2200‐based all‐PSCs. The two‐dimensional Cd 0.85 PS 3 Li 0.3 possess enormous surface area that can serve as the nucleation center, inducing the crystallinity of D/A without influencing the original phase separation. Such feature significantly boosted the charge transport, PCE (from 7.18% to 8.79%) and stability of PBDB‐T:N2200‐based device. Moreover, the Cd 0.85 PS 3 Li 0.3 nanoparticle dopant was proved to be universal in non‐fullerene small molecule acceptor (NFSMA)‐based organic solar cells (OSCs), for which the PCE was boosted from 15.05% to 17.27% for PM6:L8‐BO‐based OSCs and from 17.29% to 19.10% for D18:L8‐BO‐based OSCs. These observations exemplify the significance of two‐dimensional TMPTCs nanoparticle dopant as a tool for breaking the rock‐ribbed trade‐off between the crystallinity and phase separation scale of D/A in OSCs, which may open up a special field for making two‐dimensional TMPTCs work in a unprecedented way in OSCs.