Waterproof Stability Research Articles

Flexible Single-Crystal Perovskite Photodetectors via Polymer-Controlled Transfer.

The large-sized perovskite single-crystal sheet (SCS) serves as the ideal research platform for perovskite photodetectors due to its outstanding carrier photophysics, pronounced geometric aspect ratio, and ultrahigh material utilization rate. However, its performance in flexible device applications is relatively lackluster due to the rigid and brittle nature of the three-dimensional cubic lattices. In this work, the indium tin oxide (ITO)-based multimillimeter-sized MAPbBr3 SCS is transformed into MAPbI3 SCS via ion exchange strategy. Significantly, we proposed and implemented a polymer-controlled transfer strategy─utilizing the dichloromethane (DCM) solution of poly(methyl methacrylate) (PMMA)─to nondestructively transfer the whole perovskite SCS off the ITO substrates and subsequently adhere it onto a flexible polyethylene terephthalate (PET) substrate of interdigital electrode, thereby fabricating a lateral-structured photodetector with a PMMA-SCS-Au-PET multilayer configuration. The tight self-encapsulation between the top PMMA membrane and the bottom PET substrate imparts excellent waterproof stability and concurrently excellent mechanical flexibility to these devices; additionally, the MAPbI3 device exhibits comprehensively superior performance to the MAPbBr3 one. This work represents a proactive attempt and exploration of the high-performance advancement of large-sized SCS photodetectors, undoubtedly introducing novel momentum and solutions to this domain.

Moisture‐Resistant Orange Emitters with Near‐Unity Quantum Yield from Mn2+ Alloyed Vacancy‐Ordered Quadruple Perovskites

AbstractMn2+‐doped metal halide perovskites present remarkable optical properties in optoelectronic applications, although the realization of high efficiency and stability is still a challenge. In this work, a series of highly efficient and stable orange‐emitting Mn2+ alloyed Cs4Cd1‐xMnxBi2Cl12 single crystals are successfully synthesized via a hydrothermal reaction. Combined with the crystal structure and spectral characterization at 7 K, the site occupation of Mn2+ and defect emission are systematically discussed. Benefiting from the effective [BiCl6]3−→[MnCl6]4− energy transfer and lattice distortion, these single crystals exhibit a maximum internal and external quantum yield of ≈97% and ≈65% at 35% heavy doping level. Interestingly, these Mn2+‐alloyed single crystals exhibit remarkably waterproof stability, no decrease in emission intensity is observed after immersion in deionized water for 4 h. After soaking in deionized water for 100 days, the internal quantum yield can still maintain 44%, implying good chemical stability and moisture resistance due to the formation of protective BiOCl layer. This work provides new insights into the optimization mechanism for Mn2+ luminescence and overcoming the downside of their waterproofing in humid conditions.

Key role of Nb5+ in achieving water-resistant red emission in K2Ta1-xNbxF7:Mn4+ phosphors

Mn4+-activated fluoride is one of the most important red phosphors for white light-emitting diodes (WLEDs) with high color rendering index (CRI). Due to a lack of water resistance, their potential applications are limited. Although surface coating strategies improve the waterproof stability of fluoride red phosphors, they have downsides. It was found that Nb5+ plays an important role in improving the water resistance of Mn4+-activated oxyfluorides by preventing the hydrolysis of [MnF6]2-. In this work, the influence of Nb5+ on the waterproof stability of Mn4+-activated fluorides was explored. A set of synthesized K2Ta1-xNbxF7:Mn4+ phosphors exhibit tunable and superior water resistance. The photoluminescence (PL) intensity of the representative sample K2Ta0.6Nb0.4F7:5%Mn4+ remains nearly 100% of its initial value even after being immersed in water for 60 min, which is significantly higher than the commercial K2SiF6:Mn4+ red phosphor (8.7%). Our findings open up new possibilities for the development of waterproof fluoride red phosphors.

Mn4+ activated dodec-fluoride red phosphor Na3Li3In2F12:Mn4+ with excellent waterproof stability for WLEDs

Mn4+ activated fluoride red phosphors, as candidate red materials in white light-emitting diodes (WLEDs), have received widespread attention. However, the poor water stability limits their application. Herein, a novel dodec-fluoride red phosphor Na3Li3In2F12:Mn4+ with good waterproof stability was successfully synthesized by solvothermal method. The crystal structure, optical property, micro-morphology, element composition, waterproof property and thermal behavior of Na3Li3In2F12:Mn4+ phosphor were analyzed. Under the 468 nm blue light excitation, the Na3Li3In2F12:Mn4+ phosphor has narrow emission bands in the area of 590–680 nm. Compared with commercial red phosphor K2SiF6:Mn4+, the Na3Li3In2F12:Mn4+ phosphor possesses better waterproof stability. When soaked in water for 360 min, the PL intensity of the Na3Li3In2F12:Mn4+ phosphor remains at initial 80%. Finally, warm WLEDs with CRI of 87 and CCT of 3386 K have been fabricated using blue InGaN chip, YAG:Ce3+ yellow phosphor and Na3Li3In2F12:Mn4+ red phosphor.

A novel Mn4+-activated fluoride red phosphor Cs30(Nb2O2F9)9(OH)3·H2O:Mn4+ with good waterproof stability for WLEDs

Due to the presence of Nb5+, a Mn4+-doped compound (denoted as CNOFM) shows very good waterproof stability, even without any surface modification. Warm WLEDs with a high color rendering index have been fabricated using the CNOFM red phosphor.

Single-Crystal Red Phosphors and Their Core-Shell Structure for Improved Water-Resistance for Laser Diodes Applications.

A solvent-vapor transport route produces centimeter-sized single-crystal red phosphors. The epitaxial growth route to yield its core-shell structure at ambient temperature was adopted. These red phosphors could be applied in all-inorganic WLED devices. Cs2 TiF6 :Mn4+ (CTFM) single crystal provides enhancement of quantum efficiency, moisture resistance, and thermal stability compared to polycrystalline powders. The internal quantum efficiency can reach as high as 98.7 %. To further improve waterproof stability, the Cs2 TiF6 (CTF) shell with tunable thickness has been epitaxially grown on the CTFM single crystal surface and a unique three-step photoluminescence intensity evolution mechanism has been proposed. By combining as-prepared CTFM@CTF core-shell structured single crystal, YAG:Ce single crystal and blue-chip, warm WLEDs with excellent color rendition (Ra =90, R9 =94), low correlated color temperature (CCT=3155 K), and high luminous efficacy were fabricated without any organic resins.

Single‐Crystal Red Phosphors and Their Core–Shell Structure for Improved Water‐Resistance for Laser Diodes Applications

AbstractA solvent‐vapor transport route produces centimeter‐sized single‐crystal red phosphors. The epitaxial growth route to yield its core–shell structure at ambient temperature was adopted. These red phosphors could be applied in all‐inorganic WLED devices. Cs2TiF6:Mn4+ (CTFM) single crystal provides enhancement of quantum efficiency, moisture resistance, and thermal stability compared to polycrystalline powders. The internal quantum efficiency can reach as high as 98.7 %. To further improve waterproof stability, the Cs2TiF6 (CTF) shell with tunable thickness has been epitaxially grown on the CTFM single crystal surface and a unique three‐step photoluminescence intensity evolution mechanism has been proposed. By combining as‐prepared CTFM@CTF core–shell structured single crystal, YAG:Ce single crystal and blue‐chip, warm WLEDs with excellent color rendition (Ra=90, R9=94), low correlated color temperature (CCT=3155 K), and high luminous efficacy were fabricated without any organic resins.

High moisture resistance of an efficient Mn4+-activated red phosphor Cs2NbOF5:Mn4+ for WLEDs

Mn4+-activated fluoride red phosphors, the most important red phosphors for warm white light emitting diodes (LEDs), usually suffer from inherent poor moisture resistance which is a major obstacle to their long-lasting outdoor applications in a high humidity environment. Surface modification of phosphors by coating with either organic or inorganic shells is an effective way to improve waterproof stability. However, the coating procedure usually has a negative impact on the luminous efficacy due to the increased passivation shell thickness. In this work, Mn4+-activated oxyfluoroniobate (Cs2NbOF5), a highly efficient phosphor with internal quantum efficiency of ca. 82%, has been successfully synthesized and it is interesting to note that Cs2NbOF5:Mn4+ can exhibit remarkably improved waterproof stability even without surface coating compared to well-accepted commercial fluoride red-emitting phosphor, K2SiF6:Mn4+. The results obtained indicate that Nb5+ ions inside red phosphor play a crucial role in improving the water-resistant performance of Mn4+, which provides a new concept for overcoming the downside of their waterproof in humid conditions and maintaining the luminescence efficiency. In the final phase white LEDs with a high luminous efficacy of 174 lm/W (higher than commercial fluoride red phosphors), low correlated color temperature (3164 K) and high color rendering index (Ra = 90 and R9 = 85) have been fabricated using Cs2NbOF5:Mn4+.

Facilely Electrophoretic Derived Aluminum/Zinc (II) Oxide Nanocomposite with superhydrophobicity and thermostability

Developed energetic composites (e.g. aluminum/zinc (II) oxide) with superhydrophobicity and outstanding thermostability destine to be an attractive new generation of energy materials with wide applications. In this work, the superhydrophobic aluminum/zinc (II) oxide coatings (SAZECs) have been designed by electrophoretic deposition (EPD) of components co-scattered in optimal stable suspension of isopropyl alcohol, acetylacetone, and polyethyleneimine as the effect additive, followed by surface energy reducing treatment. Combining energy dispersive X-ray, field emission scanning electron microcopy and X-ray diffraction, we characterized target coatings with relative even distribution and high purity. Wettability analysis results indicated that the SAZECs possessed both high water contact angle (CA) of ~168° and severe exothermic property with heat-release up to 1.88 × 103 J/g. Moreover, product showed excellent water-proof stability and thermostability after twelve months exposure experiments. This work demonstrates fundamental insights for the superhydrophobic energetic materials enabled by rationally designing electrophoretic co-assembly of charged particles, thus possessing universal significance in improving MICs life time while offering a facile reference to design other self-protected MICs for real industrial application.

Large area, waterproof, air stable and cost effective efficient perovskite solar cells through modified carbon hole extraction layer

The conventional unstable and expensive hole transporting materials (HTM) has been replaced by cost effective modified carbon hole extraction layer. Herein, we demonstrated a new recipe toward air stable and waterproof modified carbon hole extraction layer for efficient perovskite solar cells (PSCs). The commercial available carbon ink modified with methylammonium lead iodide (MAI) has been used as hole extraction layer for ambipolar perovskite solar cells. The fabricated optimized perovskite solar cell having Glass/FTO/mp-TiO2/MAPbI3-xClx/carbon + MAI/Carbon configuration exhibited η = 13.87% power conversion efficiency (PCE) with open circuit voltage (VOC) 0.997 V, current density (JSC) = 21.41 mAcm−2 and fill factor (FF) 0.65. Furthermore, the air stability were tested at room temperature in open atmosphere. The water proof stability was tested under water flushing. Our results revealed that, although our carbon based devices show lower PCE (η = 13.87%) compared to spiro-MeOTAD HTM (η = 15%), the fabricated PSCs could even retain >90% after water exposure >20 times and ambient air stability more than 160 days. Further the large area device (>1 cm2) device shows 13.04% PCE with Jsc = 21.47 mAcm−2, VOC = 0.996 V and FF = 0.61. We have also demonstrated >13% efficiency for large area device (>1.1 cm2), demonstrating that the developed method is simple, cost effective and promising towards large area device fabrication. The developed methodology based on low cost carbon hole extraction layer will be helpful towards waterproof and air stable perovskite solar cells for large-area devices.

Sustainable Hydraulic Barrier Design Technologies for Effective Infrastructure Engineering

Migration of liquids lead to embarrassing post construction scenarios such as that of leaks from roofs, potable water leaking from water tanks/ reservoirs, rising damp in walls with groundwater seeping into basement structures, leakage of water from ornamental lakes and ponds or leachate leakage into the environment from MSW landfill sites. Such failures demand immediate and expensive maintenance. A stringent control on structural and waterproof stability is deemed necessary for long term service life of structures and in particular underground and near surface structures. On a micro scale and over a longer time scale, the phenomenon of rising dampness occurs in older buildings with the groundwater rising up through walls, floors and masonry via capillary action. Even slower rates of contaminant fluid migration occur through landfill base liners. In this paper a variety of hydraulic barrier technologies is critically discussed against a backdrop of relevant case studies. The choice of an appropriate hydraulic barrier technology for a given scenario will depend also on the sustainability, financial affordability and subjective aesthetics.

Effects of Geometrical Shapes of Wood Particles on the Mechanical and Water-Uptake Properties of the Resulting Wood/High Density Polyethylene Composites

Waste wood particles of different shapes were used to reinforce high density polyethylene (HDPE) to prepare high performance wood/plastic composites (WPC). The wood particles showed a needle-, flake-, strand-, and powder-shape, respectively. The mechanical and water-uptake properties of the composites manufactured using extrusion were tested. The wood needles/HDPE composites (WN-WPC) exhibited slightly higher mechanical strengths and lower density than the composites with the other shapes of wood particles. When the flake-, strand-, and powder-shaped wood particles were replaced by wood needles, the flexural, tensile and impact strengths were increased approximately by 4.24%, 7.61%, and 16.6% on average, respectively, and the density was decreased by about 7.34%. The length and width of WPC specimens changed little when soaked in water, with the thickening on the edge area only. WN-WPC performed the best waterproof stability. Based on the experimental results, the wood needles with lager length-to-diameter ratio would be the most suitable for producing high performance WPC.