Supramolecular Association of Pyrrolidinofullerenes Bearing Chelating Pyridyl Groups and Zinc Phthalocyanine for Organic Solar Cells

We investigated donor−acceptor bilayer heterojunctions formed by deposition of solution-processed pyrrolidinofullerenes bearing chelating pyridyl groups (PyFs) on vacuum-evaporated films of zinc phthalocyanine (ZnPc). It is shown that coordination complexes are formed at the interface between these donor and acceptor components; such association facilitates photoinduced charge separation and results in improved performance of the photovoltaic devices. Thus, the bilayer photovoltaic cells fabricated from different pyrrolidinofullerenes and ZnPc exhibit short circuit current (Isc) densities in the range of 3−5 mA/cm2, open circuit voltages (Voc) of 400−600 mV, and fill factors (FF) of 40−50% that correspond to power conversion efficiencies (η) of up to 1.5% under 100 mW/cm2 simulated AM1.5 illumination. The reference cells based on the nonchelating fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) as acceptor component yield lower power conversion efficiencies (0.4−0.6%); the performanc...