Photopolymerization effects on the external quantum efficiency of fullerene/zinc phthalocyanine heterojunction solar cells

Abstract

We have demonstrated that the external quantum efficiency (EQE) of organic photovoltaic cells with a heterojunction of zinc phthalocyanine (ZnPc) and fullerene (C60) bilayer films, which are used as a donor and an acceptor, respectively, is improved by photopolymerization (photon energy: 2–4 eV and light fluence: 0.4 W cm−2) between adjacent C60 molecules via a [2 + 2] cycloadditional four-membered ring. Comparison of the structural and physical properties of ZnPc, C60, and ZnPc/C60 bilayer films between before and after photoirradiation indicated that an increase in the number of photogenerated intra- and inter-molecular excitons in photopolymerized C60 film mainly contributes toward improvement of the EQE in a wavelength range of 400–600 nm.