CsPbBr 3 single crystals have potential for application in ionizing-radiation detection devices due to their optimal optoelectronic properties. Yet, their mixed ionic–electronic conductivity produces instability and hysteretic artifacts hindering the long-term device operation. Herein, we report an electrical characterization of CsPbBr 3 single crystals operating up to the time scale of hours. Our fast time-of-flight measurements reveal bulk mobilities of 13–26 cm 2 V –1 s –1 with a negative voltage bias dependency. By means of a guard ring (GR) configuration, we separate bulk and surface mobilities showing significant qualitative and quantitative transport differences. Our experiments of current transients and impedance spectroscopy indicate the formation of several regimes of space-charge-limited current (SCLC) associated with mechanisms similar to the Poole–Frenkel ionized-trap-assisted transport. We show that the ionic-SCLC seems to be an operational mode in this lead halide perovskite, despite the fact that experiments can be designed where the contribution of mobile ions to transport is negligible.
The lifetime of a carrier is a crucial parameter for solar cell materials, and metal halide perovskite materials are promising for solar cell applications. In this study, we observed carrier recombination using time-resolved photoluminescence (TR-PL) and microwave photoconductivity decay (μ-PCD) in metal halide perovskite materials: NH3CH3PbI3 (MAPbI3), NH3CH3PbBr3 (MAPbBr3), and CsPbBr3 with single- and poly-crystalline structures. By comparing the decay curves of TR-PL and μ-PCD, we found trap levels in the band gap for all the materials. We employed two excitation wavelengths for the μ-PCD measurements, and we observed faster μ-PCD signal decays for short wavelength excitation for MAPbBr3 and CsPbBr3. Additionally, we established that the poly-crystals exhibited faster decay compared with the single crystals for MAPbBr3 and CsPbBr3. Therefore, we concluded that there are significant contributions of the interface and surface recombination on carrier recombination for MAPbBr3 and CsPbBr3, but not for MAPbI3.
Spinel chromite nanoparticles are prospective candidates for a variety of applications from catalysis to depollution. In this work, we used a sol–gel auto-combustion method to synthesize spinel-type MgCr2O4 nanoparticles by using fructose (FS), tartaric acid (TA), and hexamethylenetetramine (HMTA) as chelating/fuel agents. The optimal temperature treatment for the formation of impurity-free MgCr2O4 nanostructures was found to range from 500 to 750 °C. Fourier transform infrared (FTIR) spectroscopy was used to determine the lattice vibrations of the corresponding chemical bonds from octahedral and tetrahedral positions, and the optical band gap was calculated from UV–VIS spectrophotometry. The stabilization of the spinel phase was proved by X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) analysis. From field-emission scanning electron microscopy (FE-SEM), we found that the size of the constituent particles ranged from 10 to 40 nm. The catalytic activity of the as-prepared MgCr2O4 nanocrystals synthesized by using tartaric acid as a chelating/fuel agent was tested on the decomposition of hydrogen peroxide. In particular, we found that the nature of the chelating/fuel agent as well as the energy released during the auto-combustion played an important role on the structural, optical, and catalytic properties of MgCr2O4 nanoparticles obtained by this synthetic route.
The all-inorganic perovskite cesium lead bromide (CsPbBr 3 ) has attracted considerable attention as a promising material for optoelectronics and high-energy radiation detectors. In order to obtain a bulk single crystal from a melt, it is crucial to understand the peculiarities of melting and crystallization processes. Here, the solid−liquid and liquid−solid phase transitions were studied by differential thermal analysis at different heating/cooling rates (0.1, 1, 3, 5, and 10 °C/min). A two-stage melting mechanism of CsPbBr 3 perovskite was proposed. The critical maximal sample temperature (T critical ) was determined for each heating rate. If the sample was heated to a temperature below T critical , the crystallization occurred at a temperature higher than the melting point. Contrarily, if the sample was heated to a temperature higher than this critical value, the melt crystallization occurred with supercooling. We believe that such crystallization features are closely related to the melt structure, which changes during the sample heating. The activation energies of melting and crystallization processes of CsPbBr 3 were determined to be 1846 and 1940 kJ/mol, respectively. For the first time, this study demonstrates the impact of heating and cooling conditions on the melting and crystallization processes of the bulk CsPbBr 3 . It is significant for gaining a fundamental understanding of the crystal growth and fabrication of high-quality monocrystalline materials.
The synthesis of aqueous CdTe/CdS quantum dots (QDs) embedded in potassium dihydrogen phosphate KH2PO4 (KDP) is demonstrated.
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