Ion migration and dark current suppression in quasi-2D perovskite-based X-ray detectors

Cesium-based lead-free double perovskite materials (Cs₂AgBiBr₆) have garnered significant attention in the X-ray detection field due to their environment friendly characteristics. However, their substantial ion migration properties lead to large dark currents and detection limits in Cs₂AgBiBr₆-based X-ray detectors, restricting the detection performance of the device. In terms of process technology, ultrasonic spraying is more suitable than a spin-coating method for fabricating large-area, micron-scale perovskite thick films, with higher cost-effectiveness, which is crucial for X-ray detection. This work introduces a BA⁺ (BA⁺ = CH₃CH₂CH₂CH₂NH₃ ⁺, n-butyl) source into the precursor solution and employs ultrasonic spraying to fabricate quasi-two-dimensional structured polycrystalline (BA)₂Cs₉Ag₅Bi₅Br₃₁ perovskite thick films, developing a low-cost, eco-friendly X-ray detector with low dark current density and low detection limit. Characterization results reveal that the ion migration activation energy of (BA)₂Cs₉Ag₅Bi₅Br₃₁ reaches 419 meV, approximately 17% higher than that of traditional three-dimensional perovskites, effectively suppressing perovskite ion migration and subsequently reducing the dark current. The (BA)₂Cs₉Ag₅Bi₅Br₃₁-based X-ray detectors exhibit high resistivity (about 1.75 × 10¹⁰ Ω cm), low dark current density (66 nA cm^-2), minimal dark current drift (0.016 pA cm^-1 s^-1 V^-1), and detection limit (138 nGy_air s^-1), holding considerable promise for applications in low-noise, low-dose X-ray detection.