Packing and Disorder in Substituted Fullerenes

Fullerenes are ubiquitous as electron-acceptor and electron-transport materials in organic solar cells. Recent synthetic strategies to improve the solubility and electronic characteristics of these molecules have translated into a tremendous increase in the variety of derivatives employed in these applications. Here, we use molecular dynamics (MD) simulations to examine the impact of going from monoadducts to bis- and tris-adducts on the structural, cohesive, and packing characteristics of [6,6]-phenyl-C₆₀-butyric acid methyl ester (PCBM) and indene-C₆₀. The packing configurations obtained at the MD level then serve as input for density functional theory calculations that examine the solid-state energetic disorder (distribution of site energies) as a function of chemical substitution. The variations in structural and site-energy disorders reflect the fundamental materials differences among the derivatives and impact the performance of these materials in thin-film electronic devices.