Diblock polymers containing fullerene yield stable organic solar cells upon thermal annealing. Fullerides are chemical compounds containing fullerene anions. It also corresponds to the geometry of the fullerene C ("buckyball") molecule. A nanotube is a member of the fullerene structural family, which also includes buckyballs. They are normally composed of a conjugated molecule based donor and fullerene based acceptor. The crystal structure contains toluene molecules packed between the spheres of the fullerene. Single terbium atoms have been isolated by implanting them into fullerene molecules. The endohedral fullerene molecules formed are stable at high temperatures. Two helium atoms can be confined together without bonding in the cage of a fullerene. Optimized structures of many fullerene isomers are published and listed on the web. The smallest possible fullerene is the dodecahedral . They were discovered in 1993 and greatly expand the overall fullerene class of compounds. C(OH) was prepared using a multistep procedure starting from a mixed peroxide fullerene. Radon caged inside a fullerene has been proposed as a drug for tumors. Fullerene production generally starts by producing fullerene-rich soot.