We have synthesized n-n isotype organic heterojunction comprising of n-type cobalt hexadecafluorophthalocyanine (F₁₆CoPc)/n-type tris(8-hydroxyquinoline)zinc (Znq₃) thermal evaporation method. Using Kelvin probe we found that electrons are accumulated at F₁₆CoPc and depleted in Znq₃ sides of interface. The total thickness of electrons accumulation and depletion were found to be 16 nm. Electron accumulation was further confirmed by charge transport measurement.