Highly Flexible X-ray Detectors Based on Pure Inorganic Metal Iodide Polycrystalline Thin Films as Photon-to-Charge Conversion Layers

Pure inorganic metal iodide (M = Pb, Bi) represents a family of promising materials for X-ray detection realizing photon-to-charge conversion directly. The high-atomic-number elements (Pb, Bi, I) leading to a high absorption coefficient as well as a relatively large band gap endow a low dark current prompting low noise and high sensitivity. The ionic bond and van der Waals bond are both contained simultaneously in the metal iodide with a layered crystal structure which will endow a low Young’s modulus and small hardness to develop a kind of practical flexible X-ray detector potentially. To verify this conception, the highly flexible X-ray detectors built by pure PbI2 and BiI3 polycrystalline thin films on plastic substrate as conversion layers are fabricated mainly by using electron beam evaporation and laser engraving. The dark current 13–20 pA and photocurrent 108–110 pA for BiI3-based detectors is obtained with 10 V bias voltage and X-ray exposure, while the dark current and photocurrent are 2–6 and 42–45 pA for PbI2 devices. A consistent response from both detectors is obtained at various bending states, and the degradation of dark current and photocurrent is less than 10% via 100 cycles of the bending test. These results suggest that the pure inorganic metal iodide thin films are potential candidates for flexible X-ray detector development.