Broadband photodetectors simplify multiband sensing by eliminating the need for complex integration of multiple narrow-band devices. Polyoxometalates (POMs), known for their excellent electronic properties and redox activity, enhance this functionality by promoting efficient charge transport and light absorption. In this study, we synthesized a Dawson-type germanium-doped polyoxometalate to explore its photodetection capabilities across the UV–Vis–NIR spectrum. The compound was thoroughly characterized using 31P NMR, FT-IR, UV–Vis spectroscopy, cyclic-voltage (C-V) profiling, SEM, EDX, TEM, and AFM analyses. The fabricated device demonstrated a notable rectification ratio of 1383.62. Under solar illumination, it achieved a minimum noise equivalent power (NEP) of 1.2 × 10–12 WHz−1/2 and a high detectivity of 7.42 × 1010 Jones. Its performance was further evaluated across wavelengths from 351 to 1600 nm without applying external bias, highlighting its potential as a self-powered photodetector. At 1000 nm (6.8 mW/cm2), the device exhibited a responsivity of 22.49 mA/W and a detectivity of 1.46 × 1010 Jones, confirming its suitability for broadband, self-powered UV–Vis–NIR photodetection applications.