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

摘要

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(I_(sc))densities in the range of 3-5 mA/cm~2,open circuit voltages(V_(oc))of 400-600 mV,and fill factors(FF)of 40-50 that correspond to power conversion efficiencies(eta)of up to 1.5 under 100 mW/cm~2 simulated AM1.5 illumination.The reference cells based on the nonchelating fullerene derivative 6,6-phenyl-C_(61)butyric acid methyl ester(PCBM)as acceptor component yield lower power conversion efficiencies(0.4-0.6);the performance of such devices can be increased significantly by mixing PCBM with a small amount(4 w/w)of PyF in the acceptor layer.A novel multicomponent organic solar cell architecture is suggested in order to expand the active layer absorption by formal combination of the solution-processed bulk heterojunction polymer/fullerene cells with evaporated bilayer ZnPc/fullerene devices.For this purpose,a blend of the fullerene derivatives(PCBM and PyF mixed in different ratios)with the polyconjugated polymer poly((2-methoxy-5-(3,7-dimethyloctyloxy)-p-phenylene)vinylene(MDMO-PPV)is spin-coated on the ZnPc film sublimed on an indium tin oxide(ITO)substrate.Evaporation of the top aluminum electrodes yields photovoltaic devices that demonstrate power conversion efficiencies of up to 2 and efficient photocurrent generation in the full range from 350 to 820 nm.