Surface passivation of halide perovskite nanocrystals for stable and high purity color conversion
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Surface passivation using aminopropyl-functionalized siloxane is proposed via a post-synthesis ligand exchange reaction. The near-unity photoluminescence quantum yield (PLQY) is explained by more efficient surface passivation, which is confirmed by transient PL measurements. Alternatively, the siloxane can be introduced during the hot-injection synthesis, and a thicker SiO2 shell structure is formed on the surface of nanocrystals (NCs), which leads to agglomeration and degrades optical properties. The low-temperature ligand exchange reaction lends precision process control; thereby, an optimized PLQY of 99% is achieved. Moreover, the emission wavelength of the siloxane passivated CsPbBr3 can be modulated via halide exchange for highly saturated and stable green emissions. The stability of these NCs is first ascribed to the siloxane moiety. Siloxane passivated CsPbI3 NCs were also prepared with bright red emission. A wide color gamut of 134.9% National Television System Committee or 100.7% Rec. 2020 is realized using blue light-emitting diodes together with green and red perovskite NCs. We stress the effect of Cs vacancy repair via the ligand exchange and the essentially monolayer thickness of the ligand shell to ascribe the high performance of these NCs.Keywords:
Passivation
Siloxane
Quantum yield
Nanocrystalline material
Stability of the passive 18-8 steel in acid solution is found to depend on the potential during the etching treatment as well as the passivation treatment. The potential of the steel during the passivation treatment is controlled by changing the concentration of nitric acid solution or by using a potentiostat. Also a constant potential of the steel during the etching treatment is attained in a dilute nitric acid solution or in a concentrated sulphuric acid solution with or without applying the external polarization. Stability which is decided by measuring the self-activation time in oxygen-free sulphuric acid solution increases with increasing the potential of the passivation treatment, and a critical potential, at which the stability changes abruptly, is admitted irrespective of the method of the passivation treatment, i. e., chemical passivation or potentiostatically controlled passivation. Structural changes of the passive film are concluded to take place at this critical potential of 0.4 volt (vs. SCE). Etching potential, also, changes the self-activation time of the passive steel treated at a constant passivation condition. The maximum stability is obtained at -0.32V of the etching potential. This fact is explained by assuming the selective enrichment of chromium on the surface bofore passivation.
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Nitric acid
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Duplex (building)
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The effect of the deposition and annealing temperature on the surface passivation of atomic layer deposited Al2O3 films was investigated on n-type Cz silicon wafers. The deposition temperature was varied between 200 and 500̊C and the annealing temperature between 300 and 450̊C, respectively. Films prepared at 200 and 300̊C showed an improvement of surface passivation with increasing anneal temperature. The Al2O3 films grown at 400 and 500̊C did not improve by annealing. By corona charging experiments it was revealed that the improvement in surface passivation with increasing anneal temperature of films grown at 300̊C can be attributed to a significant increase in chemical passivation with a minor increase in field-effect passivation. For Cz and FZ wafers an identical surface passivation was achieved with the chemical passivation being lower for Cz wafers due to the surface morphology and the field-effect passivation being quite similar. Consequently the field-effect passivation was found to be the more important passivation mechanism.
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Control over the growth and crystallographic orientation of nanocrystals in amorphous alloys is of particular importance for the development of advanced nanocrystalline materials. In the present study, Nd2Fe14B nanocrystals with a strong crystallographic texture along the [410] direction have been produced in Nd-lean amorphous Nd9Fe85B6 under a high pressure of 6 GPa at 923 K. This is attributed to the high pressure inducing the preferential growth of Nd2Fe14B nanocrystals in the alloy. The present study demonstrates the potential application of high-pressure technology in controlling nanocrystalline orientation in amorphous alloys.
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Floating junction (FJ) passivation is a relatively recent passivation scheme which has both experimentally and theoretically demonstrated superior passivation than either oxide or back surface field passivation. In addition, it is suited not only to high efficiency laboratory cells, but also to commercial solar cells. The improvement in surface passivation for commercial cells is an especially critical issue in achieving lower cost solar cells through reducing substrate thickness while simultaneously increasing efficiency. Despite the many advantages of FJ passivation, its applicability has been limited by the apparent inability to translate the excellent modelling results into actual solar cells. The objective of this paper is to present a complete analysis of FJ passivation and to demonstrate a method by which the problems with FJ passivation can be eliminated. Experimental evidence as well as theoretical modelling demonstrates that a solar cell with an optimized rear FJ is insensitive to parasitic effects.
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The surface properties of many inorganic electronic materials (e.g., MoS2, WSe2, Si) can be substantially modified by treatment with the superacid bis(trifluoromethane)sulfonimide (TFSI). Here we find more generally that solutions based on molecules with trifluoromethanesulfonyl groups, including TFSI, give rise to excellent room temperature surface passivation, with the common factor being the presence of CF3SO2 groups and not the solution's acidity. The mechanism of passivation comprises two effects: (i) chemical passivation; and (ii) field effect passivation from a negatively charged thin film likely to be physically adsorbed by the surface. Degradation of surface passivation is caused by de-adsorption of the thin film from the surface, and occurs slowly in air and rapidly upon vacuum exposure. The air stability of the passivation is enhanced by the presence of droplets at the surface which act to protect the properties of the film. The finding that nonacidic solutions can provide excellent electrical passivation at room temperature opens up the possibility of using them on materials more sensitive to an acidic environment.
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Degradation
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The electrochemical performance of 317L stainless steel used in medicine under different conditions of passivation (different contents of HNO3 solution, different passivation time and different passivation temperatures) was studied. The results show that the pitting potential of 317L stainless steel used in medicine can reach about 1.0 V (SCE) when electrochemically tested in 0.9% NaCl solution after the steel was passivated in 30% HNO3 solution at 35℃ for 6 h, which indicates that the passivation film has a relatively strong resistance to corrosion. The results also show that the corrosion resistance of the passivation film on the surface of 317SS can be increased after suitable amount of K2Cr2O7 is added into HNO3 passivation solution.
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An environmentally acceptable Cr-and P-free passivation agent SF-563 suitable for coating of Al wares was developed.The optimized passivation technology was established,and the properties of as-obtained passivation coating were evaluated.As the results,the optimized passivation parameters are suggested as bath concentration of 2%(mass fraction),pH value of 2.5～3.5,passivation time of 60～90 s,and passivation temperature of 10～35 ℃.Upon completion of passivation,the treated Al alloy surface does not need to be washed with water and can be directly dried at a maximum temperature of 120 ℃.Besides,the high-performance chemical conversion coating obtained under the optimized passivation parameters possesses excellent performance comparable to that of hexavalent Cr passivation coating,showing promising application in pre-treatment of Al alloy wares before coating.
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Hexavalent Chromium
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Anodizing
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