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Phthalocyanines in combination with C60 are benchmark materials for organic solar cells. Here, we have studied the morphology and electronic properties of co-deposited mixtures (blends) of these materials forming a bulk heterojunction as a function of the concentration of the two constituents. For a concentration of 1:1 of Cu-Phthalocyanine (CuPc):C60, a phase separation into about 100 nm size domains is observed, which results in electronic properties similar to layered systems. For low C60 concentrations (10:1 CuPc:C60), the morphology, as indicated by Low-Energy Electron Microscopy images, suggests a growth mode characterized by (amorphous) domains of CuPC, whereby the domain boundaries are decorated with C60. Despite of these markedly different growth modes, the electronic properties of the heterojunction films are essentially unchanged. [ABSTRACT FROM AUTHOR]