In-Situ Monitoring of the Solid-State Microstructure Evolution of Polymer: Fullerene Blend Films Using Field-Effect Transistors

Organic field-effect transistors (OFETs) are used to investigate the evolution of the solid-state microstructure of blends of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C-61-butyric acid methyl ester (PC61BM) upon annealing. Changes in the measured field-effect mobility of holes and electrons are shown to reveal relevant information about the phase-segregation in this system, which are in agreement with a eutectic phase behavior. Using dual-gate OFETs and in-situ measurements, it is demonstrated that the spatialand time-dependence of microstructural changes in such polymer: fullerene blend films can also be probed. A percolation-theory-based simulation is carried out to illustrate how phase-segregation in this system is expected to lead to a substantial decrease in the electron conductivity in an OFET channel, in qualitative agreement with experimental results.