We present a novel n-type doping technique for organic semiconductors using the metal complex bis(terpyridine)ruthenium as a strong donor. Owing to its low oxidation potential, the reduced neutral form of the donor complex allows an electron transfer to the matrix. This enables n-type conduction that has been seldom reported in metallophthalocyanine systems doped with organic compounds. The n-type zinc-phthalocyanine layers are characterized by the conductivity and the field-effect measurements. By sequential coevaporation of p- and n-doped layers, we have prepared the first stable and reproducible organic homojunction of zinc-phthalocyanine. The diode exhibits surprisingly high built-in voltage attractive e.g. for organic solar cell applications. The temperature dependence of the current-voltage characteristics does not follow the standard Shockley theory of pn-junctions. We explain the behavior of the ideality factor and the saturation current by deviations from the classical Einstein relation at low temperatures.