title: Time-resolved neutron reflectometry and photovoltaic device studies on sequentially deposited PCDTBT-fullerene layers.
abstract: We have used steady-state and time-resolved neutron reflectometry to study the diffusion of fullerene derivatives into the narrow optical gap polymer poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) to explore the sequential processing of the donor and acceptor for the preparation of efficient organic solar cells. It was found that when [6,6]-phenyl-C61-butyric-acid-methyl-ester (60-PCBM) was deposited onto a thin film of PCDTBT from dichloromethane (DCM), a three-layer structure was formed that was stable below the glass-transition temperature of the polymer. When good solvents for the polymer were used in conjunction with DCM, both 60-PCBM and [6,6]-phenyl-C71-butyric-acid-methyl-ester (70-PCBM) were seen to form films that had a thick fullerene layer containing little polymer and a PCDTBT-rich layer near the interface with the substrate. Devices composed of films prepared by sequential deposition of the polymer and fullerene had efficiencies of up to 5.3%, with those based on 60-PCBM close to optimized bulk heterojunction (BHJ) cells processed in the conventional manner. Sequential deposition of pure components to form the active layer is attractive for large-area device fabrication, and the results demonstrate that this processing method can give efficient solar cells.
authors.affiliation: Centre for Organic Photonics & Electronics, The University of Queensland , St Lucia, QLD 4072, Australia.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Clulow
authors.forename: Chen
authors.initials: C
authors.lastname: Tao
authors.forename: Kwan H
authors.initials: KH
authors.lastname: Lee
authors.forename: Marappan
authors.initials: M
authors.lastname: Velusamy
authors.forename: Jake A
authors.initials: JA
authors.lastname: McEwan
authors.forename: Paul E
authors.initials: PE
authors.lastname: Shaw
authors.forename: Norifumi L
authors.initials: NL
authors.lastname: Yamada
authors.forename: Michael
authors.initials: M
authors.lastname: James
authors.forename: Paul L
authors.initials: PL
authors.lastname: Burn
authors.forename: Ian R
authors.initials: IR
authors.lastname: Gentle
authors.forename: Paul
authors.initials: P
authors.lastname: Meredith