Organic Photovoltaic: Devices Based on Water-Soluble Copper Phthalocyanine

Organic photovoltaic (OPV) planar heterojunction devices based on an aqueous solution processed 3,4',4 '',4'"1-copper(II) phthalocyanine-tetrasulfonic acid tetrasodium salt (TSCuPc) donor layer and a fullerene (C-60) acceptor have been fabricated demonstrating power conversion efficiencies of up to 0.32% and an open circuit voltage (V-OC) of almost 0.6 V. The V-OC is significantly larger than that produced by similar cells based on the commonly studied copper phthalocyanine (CuPc)/C-60 heterojunction (V-OC = 0.46 V). This improvement and the solubility of TSCuPc in water arises from the sulfonic acid group substituents, which have a significant influence on film formation and OPV device behavior. In contrast to other solution-processed molecular semiconductors, TSCuPc forms nanocrystals in solution resulting in dense crystal thin film networks on the substrate surface. This unusual thin film morphology was studied in detail using ultraviolet-visible absorption spectroscopy, X-ray diffraction, and atomic force microscopy. Combined with current density-voltage analysis under I sun solar illumination, a deeper understanding of the molecular arrangement of TSCuPc thin films is presented as well as its impact on the resulting device behavior.