Present study shows the structural, morphological, optical characterization of sol-gel spin coated ZnO:Al film and investigation of device efficiency of Zn/ZnO:Al/p-Si/Al heterojunction diode structure. X-ray diffraction study indicates that film has hexagonal polycrystalline structure with (002) preferential direction. Atomic force microscope and scanning electron microscope images exhibit that surface of ZnO:Al/p-Si consists of homogenously scattered nanoparticles. The surface roughness of ZnO:Al film is found to be 15.24 nm. The band gap value of ZnO:Al film deposited on glass substrate is calculated to be 3.34 eV. The electrical characterization of Zn/ZnO:Al/p-Si/Al heterojunction structure is made by current-voltage (I-V) and capacitance-voltage (C-V) measurements. From these measurements, the heterojunction structure shows a rectifying behavior under a dark condition. The ideality factor and barrier height of Zn/n-ZnO:Al/p-Si/Al structure are calculated as 3.23 and 0.68 eV. The heterojunction structure have diode characteristic with rectification ratio at 64.4 at +2.0 V in the dark. The results suggest that Zn/ZnO:Al/p-Si/Al heterojunction diode can be successfully used in many optoelectronic applications.