This study investigates the electrical and optoelectronic properties of an Al/NaCo₂O₄/n-Si heterojunction device for photodetection applications. NaCo₂O₄ powder was synthesized via sol-gel electrospinning and characterized by XRD, UV-Vis, FESEM, and EDX, confirming phase purity and revealing a wide bandgap of 3.81 eV. The material was deposited on n-Si by ultrasonic spray pyrolysis to fabricate a Schottky diode, which exhibited exceptional photodiode and broadband photodetector performance. Under 2 V bias, the device achieved a high responsivity of 2.98 A/W and detectivity of 3.95 × 10¹¹ Jones. At zero bias, it demonstrated broadband sensitivity from UV to near-infrared (1100 nm), with responsivity of 1.25 mA/W and detectivity of 1.02 × 10⁹ Jones. Frequency-dependent transient measurements (100–1000 kHz) revealed ultrafast response, with rise/fall times improving from 133.9 ns/2.77 µs at 100 kHz to 36.7 ns/165 ns at 1 MHz. Impedance spectroscopy further elucidated the device’s capacitive behavior. These results position the NaCo₂O₄-interlayered heterojunction as a promising candidate for high-speed photodiodes, broadband photodetectors, and fast-switching devices.