In this work, a self-powered deep ultraviolet photodetector is introduced based on a CsPbIBr₂/Ga₂O₃ van der Waals heterojunction, fabricated via PECVD and hot-casting methods. The crystalline structure and sharp interface were comprehensively verified using X-ray diffraction (XRD) and scanning electron microscopy (SEM), showing a smooth, defect-reduced heterojunction profile with film thicknesses of ~22.52 μm for CsPbIBr₂ and ~163.88 μm for Ga₂O₃. Tauc plots verify bandgaps of 4.75 eV for Ga₂O₃ and 2.03 eV for CsPbIBr₂. According to Anderson’s rule, the CsPbIBr₂/Ga₂O₃ heterojunction forms a typical Type-II band alignment with conduction and valence band offsets of 0.68 eV (ΔE_c) and 2.90 eV (ΔE_v), which creates a robust built-in electric field across the space charge region to drive efficient photogenerated charge separation. The device delivers ultralow dark current of 1.045×10^-11 A at 10 V and a high photo-to-dark current ratio of 4.01×10³. Benefiting from the intrinsic built-in potential, stable repeatable photoresponse is realized at zero bias, demonstrating self-powered detection capability. At 10 V bias, the detector achieves a high responsivity of 0.17 A/W, an external quantum efficiency of 85% and an ultrahigh specific detectivity of 2.98×10¹² Jones under 254 nm illumination. Furthermore, transient photoresponse measurements demonstrate rapid response performance at zero bias, characterized by rising and decaying processes of 0.53 s and 0.33 s, respectively. In all, this work offers a facile strategy for high-performance self-powered solar-blind UV photodetection.