Thin films of Al-doped ZnO (ZnO:Al) are emerging as an alternative candidate to Sn-doped In2O3 (ITO) in solar cells, due to features such as non-toxic, low cost, material abundance, and high stability against a hydrogen plasma and heat cycling. The ITO/Si structure has been extensively studied during the past two decades obtained by various deposition technologies for potential application in solar cell technologies. The conversion efficiencies in solar cells from ITO/c-Si junction achieved were 10-15% using spray pyrolysis. However, little information is available in the literature on n-ZnO:Al/c-Si heterojunction in spite of its interest for the raison of its application in solar cell and other electro optics devices. Spray pyrolysis is an useful alternative to the traditional methods for obtaining thin films of pure and doped ZnO. It is of particular interest because of its simplicity, low cost and minimal waste production. The spray pyrolysis, SP, process allows the coating of large surfaces and it is easy to include in an industrial production line. In this communication, the electrical properties of n-ZnO: Alx(x = 0, 1, 2, 3, 4 %)/c-Si heterojunction prepared by SP on single-crystal n-type and p-type monocrystalline silicon (100) substrates are examined by C-V, I-V methods and admittance spectroscopy at temperature ranges between 150-373 K. The n-ZnO/c-Si heterojunctions shows a height barriers consistent with the difference of energy of the work functions of Si and ZnO; however, the n-ZnO:Al/c-Si heterojunctions present a more complex behaviour due to the defects at or near the n-ZnO:Al/c-Si interface, causing a Fermi energy pinning.