Copper sulfides (Cu x S) are compound semiconductor materials that exhibit considerable variations of optical and electrical properties. Copper sulfide thin films can be used in many applications, such as solar control coatings, solar cells, photothermal conversion of solar energy, electroconductive coatings, and microwave shielding coatings. In this paper, chemical bath deposition growth of copper sulfide thin films were monitored for the first time using an in-situ quartz crystal microbalance as a function of time, temperature, concentrations of reactants, and pH. The reaction activation energy was determined based on initial growth rates. The high activation energy, 68 [kJ/mol], indicates that the rate limiting step of the deposition is the chemical reaction rather than mass transport. The structure, morphology, composition and optical absorption of the films were studied by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and UV-Vis absorption spectroscopy respectively. These properties were found to depend strongly on the deposition conditions.

No abstract

Lead halide perovskite quantum dots (QDs) have attracted significant attention because of their excellent optoelectronic properties. In this study, we focused on reversibly modulating the photoluminescence (PL) emission of perovskite QDs using a redox cluster of polyoxometalates (POMs). Three different CsPbBr x I3–x (x = 0, 0.4, and 0.7) QDs of 9.6∼12.8 nm diameter were synthesized, stabilized by TiO2 coating, and coupled with (Bu4N)4[W10O32] (tetra-n-butylammonium decatungstate: TBADT) in organic solution. The TiO2-coated CsPbBr x I3–x (CsPbBr x I3–x @TiO2 core/shell) QDs showed bright PL emissions at 705, 678, and 605 nm, which were efficiently quenched by one-electron-reduced W10O32 5– (POM–) via photoinduced electron transfer (PET). Particularly, the PL emission at 705 nm of CsPbI3@TiO2 QDs was most efficiently quenched by 95% via PET and Förster resonance energy transfer (FRET) because of a large spectral overlap between the QD emission and POM– absorbance. The quenching mechanism was analyzed by steady-state and time-resolved PL measurements. CsPbI3@TiO2 QDs was found to photocatalytically reduce POM to POM– by visible light. The PL emission from CsPbI3@TiO2 QDs was reversibly switched between On and Off states by alternately exposing the QD–POM system to intense visible light (PL quenching via PET and FRET) and reoxidation of POM– in ambient air (PL recovery). The obtained results open the possibility of constructing perovskite QD-based photoswitches for super-resolution imaging, optical data storage, smart display, and bioimaging.

No abstract

In this work, the preparation of copper sulfide (Cu x S) thin films via microreactor-assisted solution deposition (MASD), consisting of separation of the homogeneous reaction and deposition from the molecular level heterogeneous surface reaction, is demonstrated. A particle-free flux in solution was obtained by adjusting the key process parameters, namely concentration of reactants, reaction temperature, and residence time, resulting in a high-quality film and a high deposition rate (40-100 times higher than that of films deposited by chemical bath deposition). Moreover, the growth of Cu x S thin films was monitored using an in situ quartz crystal microbalance. We found that the growth rate significantly depends on the heterogeneous temperature and residence time, while limited influence of homogeneous temperature was observed. Furthermore, conformal and dense Cu x S thin films were deposited on a highly textured Si surface that demonstrates enhanced photon absorption.

Although all-inorganic CsPbBr3 perovskites quantum dots exhibit an excellent photophysical properties, which could be applied in various applications, they still suffer from poor structural stability owing to environment factors. Therefore, TiO2 was coated on the CsPbBr3 QDs as a protecting shell to enhance their stability. Moreover, anatase phase of TiO2 shell was obtained by annealing at more than 300°C due to its most effective electron extraction properties among other crystalline forms of TiO2. However, the CsPbBr3 QDs can be degraded under high temperature. Herein, the annealing temperatures ranging from 300-500°C were optimized to obtain the anatase TiO2 shell and good crystallinity of CsPbBr3 QDs core. The morphology and optical properties of CsPbBr3 QDs, CsPbBr3/TiOx and CsPbBr3/TiO2 were studied by using transmission electron microscope (TEM), photoluminescence (PL) measurement and UV-Visible spectroscopy, respectively. Finally, the CsPbBr3/TiO2 annealed at the optimum temperature was compared with the bare CsPbBr3 QDs to prove the enhancement of their structural stability under ambient air by using X-ray diffraction (XRD).

No abstract

No abstract