Optical rectennas are expected to be applied as power sources for energy harvesting because they can convert a wide range of electromagnetic waves, from visible light to infrared. The critical element in these systems is a diode, which can respond to the changes in electrical polarity in the optical frequency. By considering trade-off relationship between current density and asymmetry of IV characteristic, we reveal the efficiency limitations of MIM diodes for the optical rectenna and suggest a novel tunnel diode using a double insulator with an oxygen-non-stoichiometry controlled homointerface structure (MOx/MOx-y). A double-insulator diode composed of Pt/TiO2/TiO1.4/Ti, in which a natural oxide layer of TiO1.4 is formed by annealing under atmosphere. The diode has as high-current-density of 4.6 × 106 A/m2, which is 400 times higher than the theoretical one obtained using Pt/TiO2/Ti MIM diodes. In addition, a high-asymmetry of 7.3 is realized simultaneously. These are expected to increase the optical rectenna efficiency by more than 1,000 times, compared to the state-of-the art system. Further, by optimizing the thickness of the double insulator layer, it is demonstrated that this diode can attain a current density of 108 A/m2 and asymmetry of 9.0, which are expected to increase the optical rectenna efficiency by 10,000.