Controlling C60 fullerene nanocolumn morphology for organic photovoltaic applications

We investigate nanostructuring approaches in inverted organic photovoltaic cells to increase exciton harvesting. Conventional bulk heterojunctions (BHJs) have disordered morphologies which increase exciton dissociation. However, in BHJs free charge carriers can be trapped in pocket domains and dead ends. Using glancing angle deposition (GLAD) we fabricate vertical nanocolumns to increase heterointerface area while improving charge transport. Nanostructured C₆₀ columns have been fabricated using GLAD on transparent indium tin oxide coated glass substrates. GLAD can control intercolumn spacing, column shape, film thickness and other properties. When depositing at constant substrate rotation vertical C₆₀ columns were achieved. Intercolumn spacing was controlled by the deposition angle between substrate and source. To further approach the ideal nanostructure for organic photovoltaic cells (OPVs), the column diameter was controlled through a substrate motion algorithm called phi-sweep. The engineered GLAD nanomorphology yielded a fivefold increase in short-circuit current when compared to planar devices and a two-fold increase in short-circuit current when compared with bulk heterojunctions.