The epitaxial growth of lead phthalocyanine on copper halogen compounds as the origin of templating effects

Abstract

Templating effects on the growth of lead phthalocyanine (PbPc) and the performance of organic photovoltaic cells (OPVs) have been investigated by using three copper halogen compounds (CuCl, CuBr, CuI), possessing different lattice parameters, as templating layers. The crystallinity of the PbPc films was highest on CuI followed by CuBr and CuCl, resulting in the broadening of the Q-band absorption in the same order. The templating effects were described by heteroepitaxial growth of organic molecules on the templating layers. The dimensionless potential calculated using a lattice model for the overlayer–substrate systems showed good correlation between the degree of epitaxy and the crystallinity of the PbPc overlayers. Furthermore, the performance of the OPVs was consistent with both the prediction from the calculation results and the observation from the optical and structural analyses.