Two-dimensional (2D) perovskites have been demonstrated great promise in x-ray detection application because of their stability, tunability, and the unique electronic properties. The centimeter-sized 2D perovskite (PMA)2PbI4 single crystal and the corresponding x-ray detector were fabricated. The Cu ion implanted device exhibits an excellent sensitivity of 283 μC Gyair−1 cm−2, the significantly enhanced mobility-lifetime (μτ) product of 8.05 × 10−3 cm2 V−1, and the lowest detectable dose rate of 2.13 μGyair s−1. Experimental observation combined with the DFT calculations shows that the improvement in Cu ion implanted x-ray detection is ascribed to the enhanced photoinduced charge carrier density and μτ product, and the increased carrier dissociation capability associated deeply with the decreased binding energy of exciton in the inorganic layer quasi-quantum well. The incorporation of the Cu interstitials by high-energy Cu ion implantation is able to introduce the donor and acceptor states with additional charge transfer channeling, resulting in the decreased exciton binding energy and fast dissociation of the exciton and the quick carrier extraction. Cu ion implantation regulating the dissociation of charge carriers in low-dimensional perovskites will motivate the application for 2D perovskite in high-performance x-ray detectors.