This invention provides a filter-free tunable spectrum PD with a layered structure of at least two electrodes and two functional layers. Both functional layers can be a layer, a stack of inorganic semiconductors, an organic semiconductor, an organic/polymer donor/acceptor blend, a hybrid semiconductor or their combinations that has a good charge transport property. The first functional layer absorbs the shorter-wavelength EM waves and is transparent to the longer-wavelength EM waves. The second functional layer absorbs the longer-wavelength EM waves. The detection spectrum window is determined by the difference in wavelengths between the transmission cut-off wavelength of the first functional layer and absorbing edge of the second functional layer, or between the absorption edge of the first functional layer and that of the second functional layer. The present PDs can be used in imaging, thermal therapy, night-vision, Li-Fi, optical communication, environmental detection, agricultural, wellness, bioimage, food, automotive and security monitoring.