Multiscale\nAnalyses of Strain-Enhanced Charge Transport\nin Conjugated Polymers

The\nadvancement of flexible and wearable electronics relies on\nsemiconducting polymers that can endure mechanical deformation while\nmaintaining high electrical performance under strain. In this study,\nwe demonstrate that fine-tuning backbone rigidity through the molecular\ndesign of donor moieties significantly enhances both the mechanical\nand charge transport properties of diketopyrrolopyrrole (DPP)-based\npolymers. Specifically, the flexible DPP-4T (quaterthiophene) exhibited\na persistence length of 20.4 nm in solution, while DPP-DTT (dithienothiophene)\nshowed a longer persistence length of 32.8 nm due to its stiff backbone,\nas confirmed by small-angle neutron scattering and Monte Carlo simulations.\nThis flexibility enabled DPP-4T to achieve a crack-onset strain exceeding\n100% via the film-on-elastomer method and a fracture strain of over\n30% in quasi-free-standing films. Additionally, DPP-4T demonstrated\na 180% increase in hole mobility at 80% strain, driven by strain-induced\nchain alignment and backbone planarization. Utilizing a range of characterization\ntechniques, including ultraviolet–visible (UV–vis) spectroscopy,\ngrazing incidence X-ray diffraction (XRD), and Raman spectroscopy,\nwe characterized structural changes at multiple length scales under\napplied tensile strain. Notably, strain induced a transformation in\nchain conformation from a twisted to a flat structure, reducing the\nhopping energy barrier and enhancing charge transport. These structural\nrearrangements are crucial for sustaining efficient charge transport\nand ensuring the reliability of electronic performance under mechanical\nstress.