to achieve reasonable responsivity, selfpowered photodetectors hold the advantages of low energy consumption, small size, light weight, and sustainability, thus attracting great attention in recent years. [6][7][8] According to the current reports, selfpowered photodetectors mainly realize detection from infrared to ultraviolet. So far, research studies on self-driven photodetectors have not been investigated fully for visible light to high-energy radiation detection toward space exploration, especially in X-ray detection. [9,10] At present, the self-powered photodetectors can be classified into two types according to their construction mechanisms. The first type is the traditional photodetector integrated with an energy harvesting unit, such as solar cell and triboelectric nanogenerators. [2,11] This architecture has been proven to be feasible, whereas the integrated parts increase the device size and weight. The other type is the heterostructure detector that exploits the photovoltaic effect to achieve self-driven photodetection. [12,13] In general, the photovoltaic effect of heterostructure photodetectors stems from the p-n junction, Schottky junction, and heterojunction, respectively. [12] These heterostructures not only absorb photons to generate electron-hole pair carriers, but also separate and transfer the photogenerated electrons and holes via their built-in potential without external power consumption. [14] These self-powered photodetectors also have the advantages of simple structure and facile fabrication processes, and have achieved tremendous progress in self-driven photodetection. [13,15] For instance, the selfdriven photodetector based on WSe 2 /Bi 2 O 2 Se demonstrates a responsivity of up to 284 mA W −1 and a response speed about 20 µs. [16] An ion migration induced self-powered photodetector reported by Dong and co-workers shows a photoresponsivity of 0.18 mA W −1 at zero bias. [17] However, most of the self-driven photodetectors based on various heterostructures possess relatively low response speed, typically from milliseconds to microseconds. [13] It remains challenge to construct ultrafast heterostructure photodetectors with self-powered ability for highenergy radiation and visible light detection.X-ray detection is crucial for applications in versatile fields, including nondestructive inspection, medical imaging and scientific research. [18][19][20][21] Suitable semiconductor materials for X-ray Self-powered halide perovskite X-ray detectors have evoked busting interests because they present outstanding properties such as low power consumption, high sensitivity, and integrability without external power source. Nevertheless, existing self-powered X-ray detectors exhibit low sensitivity due to the insufficient charge separation and transport. Herein, a self-powered photodetector for sensitive X-ray and photodetection based on single-crystalline perovskite FAPbBr 3 /NiO x heterostructure is demonstrated. The built-in field of FAPbBr 3 /NiO x heterojunction provides a driving force for separat...