Conjugated polymers incorporating flexible spacers (CP-FSs) offer a promising route to mechanically robust active layers for flexible organic solar cells. However

the influence of molecular weight distribution (MWD)—a fundamental polymer characteristic—on structural and mechanical performance remains poorly understood due to synthetic challenges. Here

we employ dissipative particle dynamics and coarse-grained molecular dynamics simulations to elucidate how MWD

quantified by polydispersity index (PDI)

governs structure-property relationships in CP-FSs. Our results reveal that PDI acts as a molecular switch controlling phase morphology: increasing PDI drives transitions from lamellar to perforated lamellar structures at intermediate rigid segment lengths. At the molecular level

higher PDI significantly increases the fraction of bridging conformations ( )

strengthening a load-bearing network. During tensile deformation

this enhanced load-bearing network suppresses destructive fibrillation and instead promotes reconstructive strengthening through dynamic loop-to-bridge transitions. These findings demonstrate that controlled MWD offers a composition-independent strategy for developing mechanically robust active layers

providing practical guidelines for flexible organic solar cell design.