Structural Analysis of Semiconducting Polymers Exposed to High Energy Radiation

Semicrystalline polymers are used in low-cost electronics such as solar cells, thin film transistors, and light-emitting diodes. Their optoelectronic performance in these devices is partly dictated by molecular ordering and nanoscale structure, where the latter is particularly difficult to control. We used atom-beam radiation to crosslink the polymer poly(3-hexylthiophene) into nanoscale and microscale patterns. Ionizing radiation sources generate intermolecular cross-links that render the polymer insoluble in organic solvents. Grazing-incidence Wide-angle X-ray Scattering (GIWAXS) was used to investigate the effects of irradiation on molecular ordering of poly(3-hexylthiophene). We found that crosslinking will disrupt intermolecular ordering (reduce crystallinity and crystalline grain sizes). We also found that X-ray exposure during the WAXS measurements can induce the crosslinking through a similar mechanism, and we propose a simple method to test for the damage caused by these measurements. As an example, we find that poly (3-hexylthiophene) has measurable cross-links after 20 sec exposure to 7.35 keV radiation with flux of $1 * 10^{11}$ photons/sec at an incident angle of 0.5$^{\circ}$ .