Broadband photodetectors that can decipher the wavelength (λ) and intensity ( I ) of an unknown incident light are urgently demanded. Photothermoelectric (PTE) detectors can achieve ultrabroadband photodetection surpassing the bandgap limitation; however, their practical application is severely hampered by the lack of deciphering strategy. In this work, we report a variable elimination method to decipher λ and I of the incident lights based on an integrated Ag 2 Se film-based PTE detector. Nanostructured Ag 2 Se films with controlled thickness are synthesized using an ion sputtering of Ag and a room-temperature selenization method and then assembled into a detector. Under identical illumination, Ag 2 Se films of different thicknesses produce varying output photothermal voltages, influenced by factors including λ. By establishing a direct relationship between the photothermal voltage and the absorption of Ag 2 Se films of varied thickness, we successfully eliminate variables independent of λ, thus determining λ. Subsequently, I is determined by the calibrated responsivity relationship using obtained λ. Our PTE detector achieves a broadband spectrum from 400 to 950 nm and high accuracy, with deviations as low as ∼2.63 and ∼0.53% for deciphered λ and I , respectively. This method allows for self-powered broadband decipherable photodetection without a complex device architecture or computational assistance, which could boost the research enthusiasm and promote the commercialization of PTE broadband detectors.