Methods in determination of morphological degradation of polymer:fullerene solar cells

The changes in the blend morphology of the thin films accelerate when thermally annealed at increased temperatures. Tapping-mode atomic force microscopy (AFM) measurements provide deeper insight into the nano- and micro-meter scale of the phase separation observable on the surface of the film. Furthermore, to prove the coarsening of phase separation on various length scales, optical microscopy, UV–Vis, photoluminescence and measurements were conducted. Of special interest is tracking down the formation of fullerene aggregates and correlation of their growth in time. We demonstrate ways to detect characteristic stages of phase separation directly using simple optical measurements.