(Invited) Spray Coating of Organic Semiconductors and Carbon Nanotube Electrodes for Solar Cells

The promise of solution processed organic solar cells lies in their low-cost high-throughput manufacturability. However, this low cost aspect can only be fully realized if all of the layers are deposited via in-line compatible methods. Spray coating is a high-rate, non-contact deposition technique characterized by the ability to deposit thin films over large areas by the superposition of small droplets. Here, we discuss our recent efforts in utilizing concurrently pumped ultrasonic spray coating, whereby two solutions are pumped to a vibrating nozzle and simultaneously atomized. With this technique, we are able to control solution concentration, donor:acceptor ratio, and multiple-solvent composition, giving us a method by which to optimize not only the smoothness and thickness of the dried film but also the active layer composition. Also, we will show our results with depositing patterned top and opaque electrodes composed of either metallic nanoparticles sintered upon deposition or multiwalled carbon nanotube (MWCNT)-based inks. Notably, despite the absorptive nature of a back MWCNT electrode, devices are able to exhibit ~85% of the photocurrent compared to an evaporated Ag top contact.