Building High-Density Polar Hybrid Perovskites via Intercalation of Cs and Aromatic Diamine for Passive X-ray Detection.

2D organic-inorganic hybrid perovskites (OIHPs) have shown great promise in direct X-ray detection. The development of high-performance passive X-ray detectors in 2D OIHPs calls for an increase in material density while maintaining structural polarity, which is becoming quite challenging. Here, a high-density, polar 2D alternating-cation-intercalated (ACI) perovskite, (4-AP)CsPbI (, 4-AP = 4-amidinopyridinium), capable of addressing this problem is successfully constructed by introducing heavy Cs into the interlayer space of an aromatic Dion-Jacobson (DJ) perovskite (4-AP)PbI (). Through such a DJ-to-ACI design, the newly developed 2D OIHP not only significantly increases its density to 4.23 g cm (even higher than that of 3D MAPbI) but also crystallizes in a polar space group (2), which further leads to enhanced X-ray attenuation and an obvious polar photovoltage (1.1 V) under X-ray irradiation. As a result, X-ray detectors fabricated by high-quality single crystals of exhibit excellent and stable detection performance under self-powered mode with a high sensitivity of 107 μC Gy cm and a low detection limit of 289 nGy s. This work provides implications for the future exploration and regulation of novel ACI OIHPs for high-performance photoelectronic devices.