Polyethylene glycol (PEG) has emerged as a promising interfacial material for enhancing the performance of Schottky-type photodetectors due to its excellent film-forming ability, chemical stability, and low-temperature processability. In this work, a PEG-interlayered Schottky photodetector was fabricated on n-type silicon substrates and systematically characterized to elucidate the role of PEG in interfacial passivation and charge transport. Structural and morphological analyses confirmed the smooth, uniform, and defect-free nature of the PEG film, while optical measurements revealed a wide band gap of 5.14 eV and high transparency in the visible region. Electrical characterization demonstrated strong rectification behavior governed by thermionic emission, with PEG effectively reducing leakage current and recombination losses. The device achieved a responsivity of up to 0.8 A/W, a specific detectivity of 1.4 × 1011 Jones, and an external quantum efficiency of 2.07%, alongside fast photo-switching times (rise/fall: 0.74/0.65 s). Importantly, the photodetector exhibited broadband sensitivity across the UV–Vis–NIR spectrum, with enhanced responsivity in the visible domain and stable performance under varying illumination intensities. These findings highlight PEG as an efficient interfacial passivation layer that enables low-noise, high-performance photodetection, offering valuable insights for the design of scalable organic–inorganic hybrid optoelectronic devices and imaging technologies.