In situ measurements of the structure and strain of a π-conjugated semiconducting polymer under mechanical load

In this work, in situ studies of organic thin films under stretching are developed. A high efficiency PffBT4T-2OD π-conjugated polymer (PCE11) was coated directly on a stretchable substrate in order to examine the impact of tensile strain on the structural properties. For that purpose, in situ grazing incidence x-ray diffraction coupled with optical microscopic observations have been carried out to measure the structural parameters of PCE11 and to probe the mechanical behavior of polymer chains under uniaxial tensile load. It is observed that in the range between 0% and 15%–20% of stretching, the polymer chains become more oriented. Meanwhile, an increase in negative values of deformation, i.e., compression of the polymer chains along the film normal was measured. Beyond this range of stretching, the polymer order declined and the stress was relaxed. This relaxation is explained by the increased number of cracks spreading over the entire film as observed using optical microscopy.