A well-organized nanoporous structure-based P–N junction photo-diode is a potential technology for next-generation optoelectronic applications because of its superior light absorption, improved mechanical strength, low density with a higher diffusion coefficient, and capacity to accommodate charges. Here, using a jet nebulizer spray pyrolysis approach to create Cd:CeO2 films as the semiconducting layer, we have created a highly sensitive P–N junction diode. The cubic fluorite crystal phases of the Cd:CeO2 films, whose crystallite size steadily increased with the Cd concentration, were proven to be polycrystalline by XRD patterns. According to the FE-SEM pictures, the Cd:CeO2 doped films with a 6 wt% Cd content displayed characteristic surface topography with spherical/elliptic and nanoporous-like morphology. With an increase in Cd content, the optical band gap energy decreased from 3.7 to 3.45 eV. We are the first to remark on the photo-diode properties of p-Si/n-Cd:CeO2 diodes, which observed a positive photoresponse with a greater reverse saturation current under lighting. This was made possible by developing the nanoporous structure of Cd:CeO2. This is corroborated by the semiconductive layer's improved detectability at higher Cd concentrations. For the diode made with 6 wt percent of Cd, we were able to attain an ultra-high responsivity of 727.57 mA/cm2, which is number of times more than that of pure CeO2. The P–N diode's inclusion of a Cd:CeO2 layer assisted in recording 342.44% quantum efficiency, making it perfect for use in ultraviolet photodiode applications.