(19e) Organic Heterojunctions for Photovoltaic Applications: C60 Growth On Pentacene

Making reliable organic electronic devices from carbon-rich (organic) semiconductors challenges researchers worldwide. There are many hurdles, one of which is making highly crystalline thin films out of organic materials. The focus in this proposal is on organic-on-organic thin film growth, which is less studied than organic-on-metal thin film growth. Specifically, the C₆₀/Pentacene organic heterojunction is a model system due to its applications for photovoltaic devices. In addition, C₆₀ and pentacene both have relatively high crystallinities, and hence relatively large charge carrier mobilities. Experimental evidence shows promising electrical properties of photovoltaic devices made from C₆₀ films grown on pentacene films. One of the main areas for improvement is in making the C₆₀ films grow in a crystalline, two dimensional manner on pentacene. Molecular Dynamics has shown the diffusive behavior of up to a few C₆₀ molecules on the bulk-phase pentacene surface; the surface diffusion coefficients of C₆₀ on pentacene are relatively liquid-like. Molecular dynamics has also shown a very interesting anisotropic diffusion behavior of C₆₀ on bulk-phase pentacene around room temperature. Kinetic Monte Carlo in combination with a continuum coalescence theory aid in the understanding of how multiple C₆₀ molecules grow on pentacene. Evidence of interesting faceted grain shapes bring understanding to the C₆₀/pentacene system. There are very little previous simulation studies of what happens at organic interfaces, and this paper will bring insight into the properties of such a system that would be otherwise hard to see experimentally or predict theoretically.