Improved Phase Stability of Formamidinium Lead Triiodide Perovskite by Strain Relaxation

Though formamidinium lead triiodide (FAPbI₃) possesses a suitable band gap and good thermal stability, the phase transition from the pure black perovskite phase (α-phase) to the undesirable yellow nonperovskite polymorph (δ-phase) at room temperature, especially under humid air, hinders its practical application. Here, we investigate the intrinsic instability mechanism of the α-phase at ambient temperature and demonstrate the existence of an anisotropic strained lattice in the (111) plane that drives phase transformation into the δ-phase. Methylammonium bromide (MABr) alloying (or FAPbI₃-MABr) was found to cause lattice contraction, thereby balancing the lattice strain. This led to dramatic improvement in the stability of α-FAPbI₃. Solar cells fabricated using FAPbI₃-MABr demonstrated significantly enhanced stability under the humid air

The Controlling Mechanism for Potential Loss in CH₃NH₃PbBr₃ Hybrid Solar Cells

We investigated moisture and thermal stability of MAPbBr₃ perovskite material. Cubic MAPbBr₃ was found to be moisture-insensitive and can avoid the thermal stability issues introduced by low-temperature phase transition in MAPbI₃. MAPbBr₃ and MAPbI₃ hybrid solar cells with efficiencies of ∼7.1% and ∼15.5%, respectively, were fabricated, and we identified the correlation between the working temperature, light intensity, and the photovoltaic performance. No charge-carrier transport barriers were found in the MAPbBr₃ and MAPbI₃ solar cells. The MAPbBr₃ solar cell displays a better stability under high working temperature because of its close-packed crystal structure. Temperature-dependent photocurrent–voltage characteristics indicate that, unlike the MAPbI₃ solar cell with an activation energy (<i>E</i>_A) nearly equal to its band gap (<i>E</i>_g), the <i>E</i>_A for the MAPbBr₃ solar cell is much lower than its <i>E</i>_g. This indicates that a high interface recombination process limits the photovoltage and consequently the device performance of the MAPbBr₃ solar cell

A pH-Responsive Yolk-Like Nanoplatform for Tumor Targeted Dual-Mode Magnetic Resonance Imaging and Chemotherapy

Incorporation of T₁ and T₂ contrast material in one nanosystem performing their respective MR contrast role and simultaneously serving as an efficient drug delivery system (DDS) has a significant potential application for clinical diagnosis and chemotherapy of cancer. However, inappropriate incorporation always encountered many issues, such as low contact area of T₁ contrast material with water-proton, inappropriate distance between T₂ contrast material and water molecule, and undesirable disturbance of T₂ contrast material for T₁ imaging. Those issues seriously limited the T₁ or T₂ contrast effect. In this work, we developed a yolk-like Fe₃O₄@Gd₂O₃ nanoplatform functionalized by polyethylene glycol and folic acid (FA), which could efficiently exert their tumor targeted T₁–T₂ dual-mode MR imaging and drug delivery role. First, this nanoplatform possessed a high longitudinal relaxation rate (<i>r</i>₁) (7.91 mM^–1 s^–1) and a stronger transverse relaxation rate (<i>r</i>₂) (386.5 mM^–1 s^–1) than that of original Fe₃O₄ (268.1 mM^–1 s^–1). Second, cisplatin could be efficiently loaded into this nanoplatform (112 mg/g) and showed pH-responsive release behavior. Third, this nanoplatform could be effectively internalized by HeLa cells with time and dosage dependence. Fourth, the FA receptor-mediated nanoplatform displayed excellent T₁–T₂ dual mode MR contrast enhancement and anticancer activity both <i>in vitro</i> and <i>in vivo</i>. Fifth, no apparent toxicity for vital organs was observed with systemic delivery of the nanoplatform <i>in vivo</i>. Thus, this nanoplatform could be a potential nanotheranostic for tumor targeted T₁–T₂ dual-mode MR imaging and chemotherapy