title: Photoinduced carrier generation and decay dynamics in intercalated and non-intercalated polymer:fullerene bulk heterojunctions.
abstract: The dependence of photoinduced carrier generation and decay on donor-acceptor nanomorphology is reported as a function of composition for blends of the polymer poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (pBTTT-C(14)) with two electron-accepting fullerenes: phenyl-C(71)-butyric acid methyl ester (PC(71)BM) or the bisadduct of phenyl-C(61)-butyric acid methyl ester (bis-PC(61)BM). The formation of partially or fully intercalated bimolecular crystals at weight ratios up to 1:1 for pBTTT-C(14):PC(71)BM blends leads to efficient exciton quenching due to a combination of static and dynamic mechanisms. At higher fullerene loadings, pure PC(71)BM domains are formed that result in an enhanced free carrier lifetime, as a consequence of spatial separation of the electron and hole into different phases, and the dominant contribution to the photoconductance comes from the high-frequency electron mobility in the fullerene clusters. In the pBTTT-C(14):bis-PC(61)BM system, phase separation results in a non-intercalated structure, independent of composition, which is characterized by exciton quenching that is dominated by a dynamic process, an enhanced carrier lifetime and a hole-dominated photoconductance signal. The results indicate that intercalation of fullerene into crystalline polymer domains is not detrimental to the density of long-lived carriers, suggesting that efficient organic photovoltaic devices could be fabricated that incorporate intercalated structures, provided that an additional pure fullerene phase is present for charge extraction.
authors.affiliation: Department of Physics, Colorado School of Mines, 1523 Illinois Street, Golden, Colorado 80401, USA.
authors.forename: William L
authors.initials: WL
authors.lastname: Rance
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Ferguson
authors.forename: Thomas
authors.initials: T
authors.lastname: McCarthy-Ward
authors.forename: Martin
authors.initials: M
authors.lastname: Heeney
authors.forename: David S
authors.initials: DS
authors.lastname: Ginley
authors.forename: Dana C
authors.initials: DC
authors.lastname: Olson
authors.forename: Garry
authors.initials: G
authors.lastname: Rumbles
authors.forename: Nikos
authors.initials: N
authors.lastname: Kopidakis