Distorted Asymmetric Cubic Nanostructure of Soluble Fullerene Crystals in Efficient Polymer:Fullerene Solar Cells - Kim, Y; Nelson, J; Zhang, T; Cook, S; Durrant, JR; Kim, H; Park, J; Shin, M; Nam, S; Heeney, M; McCulloch, I; Ha, C-S; et al. (ACS NANO, 2009)