title: Multilayer epitaxial growth of lead phthalocyanine and C(70) using CuBr as a templating layer for enhancing the efficiency of organic photovoltaic cells.
abstract: The molecular orientation and crystallinity of donor and acceptor molecules are important for high-efficiency organic photovoltaic cells (OPVs) because they significantly influence both the absorption of light and charge-transport characteristics. We report that the templating effect extends to multilayers to increase the crystallinity and to modify the orientation of the crystals of lead phthalocyanine (PbPc) and C70 layers at the same time by adopting CuBr as a new templating layer on indium tin oxide (ITO). The formation of a monoclinic phase with a preferred orientation of (320) for PbPc and a fcc phase with a preferred orientation of (220) for C70 on the PbPc layer is revealed by X-ray diffraction (XRD) patterns. The multilayer epitaxy results in an increase of the exciton diffusion lengths from 5.6 to 8.8 nm for PbPc and from 6.9 to 13.8 nm for C70 to enhance the power conversion efficiency (PCE) of the planar heterojunction OPVs composed of PbPc and C70 from 1.4 to 2.3%. The quasi-epitaxy model is proposed to explain the multilayer epitaxy.
authors.affiliation: Department of Materials Science and Engineering and the Center for Organic Light Emitting Diode, Seoul National University , Seoul 151-744, South Korea.
authors.forename: Tae-Min
authors.initials: TM
authors.lastname: Kim
authors.forename: Hyun-Sub
authors.initials: HS
authors.lastname: Shim
authors.forename: Min-Soo
authors.initials: MS
authors.lastname: Choi
authors.forename: Hyo Jung
authors.initials: HJ
authors.lastname: Kim
authors.forename: Jang-Joo
authors.initials: JJ
authors.lastname: Kim