The paper reports development of graphene/ZnO heterojunction Schottky diode structure and its structural and electrical characterization. Graphene is grown on copper substrate using chemical vapor deposition (CVD) and transferred on flexible substrate (indium Tin Oxide coated PET). The grown thin layer is characterized using scanning electron microscopy and Raman spectroscopy which confirm uniformity and high-quality graphene layer. The sputtered ZnO is deposited and characterized which confirms c-axis (002) orientation and uniform growth of ZnO film. Silver (Ag) as a top electrode has been deposited and I-V measurement has been done. The effect of operating temperature (300 K to 425 K) on I-V characteristics of the fabricated structure has been measured experimentally. The other diode parameters such as ideality factor and effective barrier height have been derived. The reliability of the heterojunction synthesized is proved by the diode ideality factor of 1.03 attained at 425 K. The excellent C-V characteristics (capacitance of 48pF) of the device prove that the device is an excellent candidate for application as supercapacitors. The fabricated structure can be utilized as an ultraviolet photodetector, solar cell, energy storage devices, etc.