Advancing spray deposition for low-cost solar cell production
Authors: K. Xerxes Steirer, Matthew O. Reese, Benjamin L. Rupert, Nikos Kopidakis, Dana C. Olson, David S. Ginley, and Reuben T. Collins
In collaboration, the Colorado School of Mines, National Center for Photovoltaics and National Renewable Energy Laboratory tested various methods of film deposition onto polymeric solar cells. In this study, ultrasonic spray technology outperformed ink jet printing, airbrush spray, slot coating and screen coating.
Ultrasonic spray technology proved to be both cost-effective and produced a uniform coating of photoconductive agents. The material tested was a solution of poly (3-hexylthiophene) (P3HT) and [6,6] phenyl-C61 butyric-methyl ester (PCBM) onto a poly (3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT: PSS) base. Both chlorobenzene and p-xylene were used as solvants and studied for their impact on cell performance. The underlying layers were Indium-tin oxide (ITO) and glass.
Ultrasonic spray technology used in the manufacture of polymeric solar cells potentially offers a means of low cost production. This study shows that solvent selection has a significant impact on cell efficiency. Authors further conclude that additional study is needed in surface morphology and solvent blending.
Ultrasonic Spray Deposition for Production of Organic Solar Cells
Authors: K. Xerxes Steirer, Matthew O. Reese, Benjamin L. Rupert, Nikos Kopidakis, Dana C. Olson, Reuben T. Collins and David S. Ginley
An element of organic photovoltaic cell construction is the use of photoactive polymers. These active agents are formed into a heterojunction film, by use of ultrasonic spray technology and carrier solvents such as chlorobenzene or p-xylene. This paper discusses in detail the different morphological patterns in film formation by use of ultrasonic spray technology, solvent used and means of film build. A 120 KHz ultrasonic nozzle system is described and the effects of deposition were carefully observed with the help of optical microscopy and small-angle x-ray diffraction.
It was discovered that p-xylene does not prove to be the ideal solvent to boost efficiency whereas chlorobenzene appears to be a more suitable. P-xylene caused a very uniform mixing and wetting effect. However when additional films were layered onto the active layers, p-xylene film exhibited unevenness. This irregular mixing does not aid the appropriate chemical reaction for electricity production thus severely reducing cell efficiency. Contrastively, chlorobenzene produced a coffee-stain effect, but with additional layering displayed an evenness of behavior that optimized the efficiency to 3.2%. In conclusion, chlorobenzene was found to be the better solvent to aid in film build using ultrasonic spray systems.