A new printable organic semiconducting material combination as a tissue equivalent photodetector for indirect X-ray detection is demonstrated in this work. The device exhibits a higher optical-to-electrical conversion efficiency than any other reported printable organic systems for X-ray photodetection while also operating efficiently with zero applied bias. Complete X-ray detectors fabricated by coupling the photodiode with a plastic scintillator are among the first flexible and fully tissue equivalent X-ray detectors capable of operating without external bias. The response to X-rays is energy independent between 50 keV and 1.2 MeV, with a detection sensitivity equivalent to inorganic direct X-ray detectors and one of the fastest temporal responses ever reported for organic X-ray detectors. The materials can be printed into arrays with a pixel pitch of 120 μm, providing 2D spatial detection. The devices are found to be highly stable with respect to time, mechanical flexing, and large (5 kGy) radiation doses. The new materials and fully tissue equivalent X-ray detectors reported here provide stable, printable, flexible, and tissue equivalent detectors with a high radiolucency that are ideally suited for wearable applications, where simultaneous monitoring and high transmission of the X-ray absorbed dose into the human body is required.