Characterizing the Morphology of Solvent Annealed PCBM/P3HT Bilayers using GIXRD and Raman Spectroscopy

A growing demand for new forms of renewable energy has been at the forefront of scientific research. Organic photovoltaics (OPVs) provide a promising alternative to the expensive inorganic solar cells used today. Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) are common donor and acceptor materials used in the active layer of an OPV device. These systems have reached power conversion efficiencies of approximately 12 %. However, little is known about the actual morphology. A better understanding of the morphology would allow researchers to optimize device fabrication to increase the device performance. As-cast devices are limited by the processing conditions which they were casted. Post-annealing allows us to alter these samples. Unlike thermal annealing, solvent annealing provides a slow, selective way to alter the samples. We looked to explore how solvent annealing affects a P3HT:PCBM bilayer. By increasing the loading of PCBM, we are able to investigate different morphologies based on the miscibility of the system. Grazing Incidence X-ray Diffraction (GIXRD), Raman spectroscopy, and Near-Edge X-ray Absorption of Fine Structure (NEXAFS) were used to explore the morphology of these systems.