Multilayer Epitaxial Growth of Lead Phthalocyanine and C_(70) Using CuBr as a Templating Layer for Enhancing the Efficiency of Organic Photovoltaic Cells

摘要

The molecular orientation and crystalliriity 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 C_(70) 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 C_(70) on the PbPc layer is revealed by X-ray diffraction (XRD) patterns. The multilayer epitaxy results in an increase of the exdton diffusion lengths from 5.6 to 8.8 nm for PbPc and from 6.9 to 13.8 nm for C_(70) to enhance the power conversion efficiency (PCE) of the planar heterojunction OPVs composed of PbPc and C_(70) from 1.4 to 2.3%. The quasi-epitaxy model is proposed to explain the multilayer epitaxy.