Real‐time in vivo detection of cancer via attenuation‐based plain X‐ray imaging is proposed to fundamentally overcome the penetration depth limits of current fluorescence‐based imaging techniques. Using cesium lead bromide (CsPbBr3, CPB) quantum dot (QD) scintillators, real‐time X‐ray detection of 5 mm‐sized Panc‐1 cell tumors grown in a mouse is successfully performed. The QDs are rapidly co‐synthesized and double‐encapsulated with silicon dioxide (SiO2) to completely prevent them from being aggregated, decomposed, or released; they are then conjugated with antibodies to target pancreatic cancer. Due to the dramatic X‐ray attenuation, the X‐ray signal from the CPB QDs placed under the 2 cm‐thick tissue is clearly observed, while their fluorescence signal is not detected at all. In in vivo mouse experiments, the injection of a tiny amount (2.8 μg on a QD basis) of the CPB–SiO2@SiO2–Ab nanoparticles gives rise to a bright spot at the location of the tumor. Cell viability assay and histological analysis confirm the biocompatibility and nontoxicity of the nanoparticles.

In this study, a new method is developed to control the Clto-I ratio in MAPbI 3−x Cl x perovskite solar cells (PSCs) more easily and precisely using single-source vapor deposition of MAPbCl 3 thin films and a subsequent anion exchange by repeated spin-coatings of methylammonium iodide (MAI) solution. This method can overcome the problems of previous vapor-deposition techniques for PSCs such as the occurrence of morphological defects in the films and difficulty in controlling the stoichiometry of the elements. The repetitive MAI treatments gradually fill the interstitial voids in the perovskite film and increase the average grain size up to 1.2 μm, which improves the charge-transfer property of the cells. The atomic Cl content, i.e., the x value, of the MAPbI 3−x Cl x film can also be simply controlled by changing the number of MAI treatments. The energy levels and resistive elements of the cells are strongly dependent on the x value of the MAPbI 3−x Cl x film. A maximum power conversion efficiency of 19.1% is achieved at x = 0.005.

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