title: Effects of alkyl chain length and substituent pattern of fullerene bis-adducts on film structures and photovoltaic properties of bulk heterojunction solar cells.
abstract: A series of alkoxycarbonyl-substituted dihydronaphthyl-based [60]fullerene bis-adduct derivatives (denoted as C2BA, C4BA, and C6BA with the alkyl chain of ethyl, n-butyl, and n-hexyl, respectively) have been synthesized to investigate the effects of alkyl chain length and substituent pattern of fullerene bis-adducts on the film structures and photovoltaic properties of bulk heterojunction polymer solar cells. The shorter alkyl chain length caused lower solubility of the fullerene bis-adducts (C6BA > C4BA > C2BA), thereby resulting in the increased separation difficulty of respective bis-adduct isomers. The device performance based on poly(3-hexylthiophene) (P3HT) and the fullerene bis-adduct regioisomer mixtures was enhanced by shortening the alkyl chain length. When using the regioisomerically separated fullerene bis-adducts, the devices based on trans-2 and a mixture of trans-4 and e of C4BA exhibited the highest power conversion efficiencies of ca. 2.4%, which are considerably higher than those of the C6BA counterparts (ca. 1.4%) and the C4BA regioisomer mixture (1.10%). The film morphologies as well as electron mobilities of the P3HT:bis-adduct blend films were found to affect the photovoltaic properties considerably. These results reveal that the alkyl chain length and substituent pattern of fullerene bis-adducts significantly influence the photovoltaic properties as well as the film structures of bulk heterojunction solar cells.
authors.affiliation: Department of Molecular Engineering, Graduate School of Engineering, and ‡Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University , Nishikyo-ku, Kyoto 615-8510, Japan.
authors.forename: Ran
authors.initials: R
authors.lastname: Tao
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Umeyama
authors.forename: Kei
authors.initials: K
authors.lastname: Kurotobi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Imahori
keywords: alky chain length; bulk heterojunction; fullerene; polymer solar cell; regioisomer