Direct conversion x-ray image detectors offer higher spatial resolution than their indirect counterparts. Organic-inorganic hybrid perovskites are among the most sensitive x-ray photoconductors for these detectors; however, high dark currents...

Scintillators are widely used for X-ray detection in various fields, such as medical diagnostics, industrial inspection and homeland security. Nanocrystals of metal halide perovskites and their analogues showed great advantages as X-ray scintillators due to their cheap manufacturing, fast decay time, and room temperature scintillation from quantum confinement effect. However, there are still many challenges unsolved for further industrialization. Herein, it is necessary to summarize the progress of scintillators based on nanocrystals of metal halide perovskites and their analogues. In first section, the scintillation mechanism and key parameters are outlined. Then, various nanocrystals of metal halide perovskites and their analogues used as scintillators are reviewed. Finally, the challenges and outlook are discussed. It is believed that nanocrystals of metal halide perovskites and their analogues are favorable for large-area and flexible X-ray detectors.

Blade coating offers a low-cost production method for fabricating perovskite thick-film x-ray detectors. However, due to the preferential nucleation at the gas–liquid interface of a perovskite solution, high-quality perovskite thick films are in such a dilemma, sacrificing either the density of the thick film by forming a porous structure or the thickness of the film through depositing a compact structure. The porous structure will lead to carrier recombination and ion migration while low thickness will cause insufficient x-ray absorption, which will increase the dark current or reduce the sensitivity of the corresponding x-ray detector. In the present work, a scalable ferroelectric dipole–methylamine lead iodide (MAPbI3) coupled x-ray detector is proposed, where the x-ray photoconductor in situ formed on indium tin oxide shows a dense fibrous mesoscopic structure oriented along the charge-carriers transport direction. It is demonstrated that ferroelectric dipoles promise not only strong coupling effects with MAPbI3, driving better crystallinity and denser assemblies, but also excellent passivation to MAPbI3 interfaces, decreasing trap-state densities, leading to improved direct x-ray detection performance. In addition, the enhanced operational stability of the corresponding device suggests a strategy of introducing the localized polarization field for stable perovskite direct x-ray detectors.

The hole transport layer (HTL) is a major component in PSCs that ensures photogenerated holes are effectively extracted. With respect to n-i-p PSCs, when lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI) and tert-butylpyridine (tBP) are employed as dopants, conventional 2,2′,7,7′-tetrakis (N, N-di-p-methoxyphenyl-amine) 9,9′-spirobifluorene (spiro-OMeTAD) is one of the most commonly used HTL materials, where it plays a significant role in fabricating high-performance devices. [1][2][3] LiTFSI is a redox inactive agent that participates in the oxidation reaction through lithium-ion consumption. This accelerates the p-doping of spiro-OMeTAD by oxygen to increase conductivity and hole mobility. [2,4,5] In addition, tBP helps promote the dispersion of Li-TFSI in HTL solution and enhances the wettability of perovskite films to improve the HTL morphology. [1,[6][7][8] However, LiTFSI has been shown to be a hygroscopic salt with a tendency to absorb moisture from air and aggregate in spiro-OMeTAD. This causes moisture-induced degradation of both the HTL and underlying perovskites. [9,10] In addition, the interaction of LiTFSI and tBP generates numerous pinholes in HTL, which accelerates the degradation of PSCs. [11,12] Finally, the top electrode of silver is unfavorable because the I − ions penetrate the spiro-OMeTAD layer through pinholes. This induces the formation of AgI, which results in critical nonradiative recombination. [13,14] On the other hand, high-performance devices often require another buffer layer between the perovskite and the conventional spiro-OMeTAD films to passivate surface defects of the perovskite layer, which increase the complexity of the device fabricating process. [15][16][17][18][19][20] Therefore, many studies have addressed spiro-OMeTAD stability and the aforementioned perovskite surface issues. In 2014, Nguyen et al. synthesized spiro-OMeTAD(TFSI) 2 by combining spiro-OMeTAD with AgTFSI, where spiro-OMeTAD + was obtained by the reaction of spiro-OMeTAD 2+ and spiro-OMeTAD. This method realized the oxidization of spiro-OMeTAD without relying on oxidation in air, thereby increasing the stability of the device. [21] In addition, compounds with TFSI − have also been proven to be a class of effective p-type dopants that can increase the stability of spiro-OMeTAD because of the Perovskite solar cells (PSCs) with n-i-p structures often utilize an organic 2,2′,7,7′-tetrakis (N, N-di-p-methoxyphenyl-amine) 9,9′-spirobifluorene (spiro-OMeTAD) along with additives of lithium bis(trifluoromethanesulfonyl) imide salt (LiTFSI) and tert-butylpyridine as the hole transporting layer (HTL). However, the HTL lacks stability in ambient air, and numerous defects are often present on the perovskite surface, which is not conducive to a stable and efficient PSC. Therefore, constructive strategies that simultaneously stabilize spiro-OMeTAD and passivate the perovskite surface are required. In this work, it is demonstrated that a novel ionic liquid of dimethylammonium bis( trifluoromethanesulfonyl)imide (DM...