(217ff) Concentration Profile of Oscillation Annealed PCBM in P3HT Films

Gas expanded liquid (GXL) deposition technology has previously been shown to anneal systems of gold nanoparticles in a monolayer on a surface. The current work will demonstrate the ability to anneal (equilibrate) fullerene or phenyl-C61-butyric acid methyl ester (PCBM) nanoparticle morphology in a 3-D film of finite thickness composed of polymeric Poly (3-hexylthiophene) (P3HT). This P3HT/PCBM thin film layer is used as an active layer in organic photovoltaic cells. Good dispersion of PCBM in P3HT results in improved performance and efficiency of the device. PCBM has been shown to adopt a nonuniform concentration profile. Annealing of the as-cast morphology is often required to realize this morphology and improve the device performance. A novel method is being developed to solvent-anneal the films, wherein solvent vapor exposure is supplemented by oscillations in solubility using the gas expanded liquid (GXL) process. The annealing process will be carried out in a specifically designed high pressure CO2 reactor. X-ray Diffraction and contact angle testing is used to characterize the P3HT/PCBM samples that are pressure annealed under different conditions.