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)Cs 2 Pb 2 I 8 ( B , 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 4 ( A ). Through such a DJ-to-ACI design, the newly developed 2D OIHP B not only significantly increases its density to 4.23 g cm -3 (even higher than that of 3D MAPbI 3 ) but also crystallizes in a polar space group ( Ama 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 B exhibit excellent and stable detection performance under self-powered mode with a high sensitivity of 107 μC Gy -1 cm -2 and a low detection limit of 289 nGy s -1 . This work provides implications for the future exploration and regulation of novel ACI OIHPs for high-performance photoelectronic devices.