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Three-electronic-dimensional (3D) lead halide perovskites show high X-ray sensitivities and a low limit of detection. However, servere ion migration causes dark current drift and worsens long-term operational stability. Although two-electronic-dimensional (2D) perovskite and 3D perovskite heterojunction devices have been shown to reduce ion migration, their current responses to X-rays have decreased considerably. A device with low ion migration without sacrificing X-ray sensitivity is needed. Atomic-thick two-dimensional (2D) materials with small pore sizes between atoms and high carrier-tunneling possibilities through them are reasonable candidates to simultaneously block ion migration and retain carrier–transport properties. Herein, a 2D monolayer of g-C3N4 was introduced into a CH3NH3PbI3 (MAPbI3) polycrystalline pellet through hot pressing. The small-sized tri-s-triazine structure of g-C3N4 could inhibit ion migration without affecting the electron transport of the perovskite pellet. As a result, the g-C3N4/MAPbI3 heterojunction pellet exhibited an ultra-low current drift of 4.87 × 10−5 nA cm−1 s−1 V−1 at an electric field of 12.66 V mm−1. Simultaneously, the detector exhibited a high sensitivity of 1.78 × 105 μC Gyair−1 cm−2 under 75.95 V mm−1 and a low limit of detection of 27 nGyair s−1 under 12.66 V mm−1, which are among the best of reported results. This work provides an effective design strategy to develop X-ray detectors with low ion migration and high detection performance. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) lead-halide perovskites with outstanding mobility-lifetime products and large attenuation coefficients for X-ray photons have demonstrated highly sensitive X-ray detection. However, there exists severe ion migration, especially under electrical bias, that results in dark-current drift and poorer device stability. Theoretical analyses suggest that 3D perovskites with two-dimensional (2D) perovskites may mitigate ion migration and reduce the dark current to achieve a drastically lower detection limit, which is badly needed for X-ray diagnostics. A bulk 2D/3D perovskite heterostructure is therefore designed and prepared by hot-pressing a mixture of BA 2 PbI 4 and MAPbI 3 particles. Compared with the pure MAPbI 3 pellet, the bulk 2D/3D heterostructure pellet shows much higher resistivity, hence, significantly reduced ion migration and a much smaller dark-current drift of 4.84 × 10 -5 nA cm -1 s -1 V -1 , which is much lower than that of the pristine MAPbI 3 pellet, thus demonstrating its effectiveness for the suppression of ion migration. The bulk 2D/3D heterostructure pellet attains an X-ray sensitivity of 2.0 × 10 3 μC Gy air -1 cm -2 as well as a lower detection limit of 111.76 nGy s -1 under 10 V bias. This work provides a successful strategy to prepare X-ray detectors with suppressed ion migration and negligible dark current drift, which will further benefit the development of lead-halide perovskite X-ray detectors.