Today I was in the mood to learn more about doped materials, and entered the EQ03.21: Next Generation Organic Semiconductors – Materials, Fundamentals and Applications I session . There I saw the “Effects of dopant size on polaron characteristics in chemically doped conjugated polymers” presentation by postdoctoral scholar Joel Bombile’s from the University of Kentucky. And was able to learn how the distance between the dopants cause an increased polaron mobility.
Their study on chemical doping used dopants of different sizes (1.13Å - 6.32Å) to inject charge carriers in 10nm conjugated polymers. They determined the dopant size and charge, which are directly related to the dopant ratio and charge mobility, respectively. Because these properties affect the induced polaron binding, they were able to determine the polaron’s mobility. This also established whether or not the polarons could move freely between the material.
Using density functional theory, the researchers noticed that as their dopant size increased, so did the polaron’s charge and size. Then by analyzing neutral and doped polymers, their data demonstrated a blue shift in the peaks of the optical absorption spectrum when the dopants were present. Finally, they found that the distance between the dopants and the polymer chain can decrease the polaron's binding energy.
If you want to learn more about how to affect the mobility of polarons in polymers, click here to view the full presentation.