Dual-Path Charge Transport Enables Decoupling of Electrical Performance Under Strain from the Crack Onset Strain in...

High electrical performance conjugated polymers (CPs) are often hard and brittle due to their planar, rigid backbones and high crystallinity, which makes maintaining superior electrical performance under mechanical strain a fundamental challenge. In this work, we address this long-standing bottleneck in flexible electronics through a novel approach. By comparing sequential doping (using copper chloride (CuCl₂) solution) and ion exchange doping (using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI):CuCl₂ solution) in poly(3-hexylthiophene) (P3HT) films, we demonstrate that the ion exchange-doped films exhibit significantly better retention of conductivity under strain, which is independent of their crack onset strain (COS). In ion exchange-doped P3HT films, TFSI^- replaces CuCl₃ ^- within the crystals and further dopes the amorphous regions, establishing two types of effective conductive pathways: crystalline-phase channels and accumulation-layer channels. This dual-path conduction mechanism ensures minimal disruption to carrier transport when tensile strain compromises the crystalline structure. As a result, the conductivity under strain is far more stable than that in sequentially doped P3HT films, which rely solely on a single crystalline-phase conductive channel despite having higher COS. This study demonstrates that increasing the diversity of carrier transport pathways offers a viable solution to a persistent challenge in flexible electronics, decoupling the strain-dependent electrical performance from COS.