To avoid foodborne illness, maintaining the prolonged food freshness and real-time food quality/health monitoring are the challenges to be addressed in this era. Development of active food packaging is an advancing research for real-time food health monitoring. In this study, mesoporous silica nanospheres (MSNs) have been synthesized with controlled size (>100nm) and porosity by using modified Stöber method. These MSNs are capable of adsorbing oxygen by physisorption thus can be used as oxygen scavengers for food packaging materials to extend shelf life of the food products. Furthermore, this study aims to incorporate active metal oxide nanoparticles (MNPs) in the pores of synthesized MSNs to extend its applications as oxygen scavenging and detection to avoid oxygen produced food degradation. The MNPs with an average size of <10 nm were successfully synthesized with stable dispersions. The active MNPs including SnO2, Fe2O3, ZnO and TiO2 (<10 nm) have been incorporated in the pores of MSNs. The MNPs were incorporated in the MSNs using i) Synthesis of MNPs followed by in-situ synthesis of MSNs, ii) synthesis of MSNs first followed by in-situ synthesis of MNPs in the pores of MSNs and, (iii) Synthesis of MSNs and MNPs separately and mixing of stable suspension of both MSNs and MNPs to achieve the best results for oxygen scavenging. The results indicated that first route was more successful for embedding the MNPs in the pores of MSNs. The oxygen scavenging efficiency of the MNPs incorporated MSNs were evaluated.
KEYWORDS: Nanoparticles, Perovskite, Atomic layer deposition, Solar cells, Thin films, Tin, Thin film solar cells, Thin film deposition, Oxides, Interfaces
Tin oxide thin is a promising electron transport layer (ETL) for perovskite solar cells due to its excellent electronic properties and high thermal stability of SnO2. In addition, unlike TiO2 and ZnO, SnO2 does not have high photocatalytic activity and therefore would improve device stability under illumination compared to devices with titania or ZnO ETLs, and it can be deposited at low temperatures which makes it compatible with flexible devices. However, surface roughness, conformal coating, surface defects of SnO2, as well as its energy level alignment with the perovskite layer, affect the performance and stability of perovskite solar cells. In this study, we utilized ALD, sol-gel deposition and nanoparticle spin coating method to prepare SnO2 thin films and apply them as ETLs for planar perovskite solar cells. The obtained results indicate that the method of preparation of SnO2 significantly affects the solar cell performance. To improve the device performance, we investigated SnO2 bilayers to attempt to combine advantages of individual coating approaches. For an optimized order of layers to achieve efficient charge extraction across the interface, improved performance can be obtained compared to single layer SnO2 electron transport layers. Reasons for the performance improvement are discussed.
Metal oxide materials for solid state gas sensors has attracted lots of attention in the past few decades due to its low fabrication cost, small device size and potential application in toxic gases detection. SnO2 is one of the favorable materials since it has outstanding performance towards the detection of various gases. Its sensing mechanism in brief was based on the change in charge carrier density of the materials due to the presence of gas molecules and the change was determined by measuring the resistance or capacitance. Despite of its great success, researches has continue to further optimize the selectivity, sensitivity, response time and more importantly lowering the working temperature of the material. In this work, SnO2 nanostructures with metal nanoclusters on the surface was prepared. The incorporation of different metal nanoclusters would offer feasibility on the selection of gas detection. The energy level alignment and the Schottky barriers at the metal-metal oxide interface would further improve the sensitivity and response time of the materials. The surface plasmon generated by the metal nanoclusters utilizing visible light could lower the operation temperature and enhance sensitivity by offering more charge carriers. The SnO2 nanofiber in this work was prepared by a scalable electrospinning method and the Ag and Au nanoclusters were prepared by sputtering or thermal evaporation. Effect of the SnO2 morphology, size and distribution of the metal nanoclusters and the illumination on the device performance will be investigated and the detail working mechanism will be discussed.
TiO2 thin film photocatalysis has suffered from poor photocatalytic efficiency due to its low surface area-to-volume ratio. The efficiency can be enhanced by narrowing the bandgap, defect engineering or introducing surface plasmonic effect. However, the fabrication process is normally complicated and time consuming. This work offers a simple method to fabricate disordered defect-rich black TiO2 ultrathin film by atomic layer deposition (ALD). Surface defects of TiO2 have been suggested to play a significant role in the process of photocatalysis. With ALD, the bandgap and surface defects of the material can be controlled effectively through the deposition parameters. Surface plasmonic effects could also be introduced by the deposition of Ag nanoclusters via simple thermal evaporation. Absorption at ~450 nm was significantly enhanced. The overall photocatalytic behavior of composite material is greatly boosted and we observed an excellent efficiency towards the degradation of organic pollutants such as bisphenol A. The mechanism of surface plasmonic enhanced black TiO2 photocatalysis was studied by in-situ infrared atomic force microscope (IR-AFM) under the illumination of different wavelength. The reaction sites of the composite materials were determined accurately and the working mechanism was discussed.
Perovskite solar cells are emerging photovoltaic technology with potential for low cost, high efficiency devices. Currently, flexible devices efficiencies over 15% have been achieved. Flexible devices are of significant interest for achieving very low production cost via roll-to-roll processing. However, the stability of perovskite devices remains a significant challenge. Unlike glass substrate which has negligible water vapor transmission rate (WVTR), polymeric flexible film substrates suffer from high moisture permeability. As PET and PEN flexible substrates exhibit higher water permeability then glass, transparent flexible backside encapsulation should be used to maximize light harvesting in perovskite layer while WVTR should be low enough. Wide band gap materials are transparent in the visible spectral range low temperature processable and can be a moisture barrier. For flexible substrates, approaches like atomic layer deposition (ALD) and low temperature solution processing could be used for metal oxide deposition. In this work, ALD SnO2, TiO2, Al2O3 and solution processed spin-on-glass was used as the barrier layer on the polymeric side of indium tin oxide (ITO) coated PEN substrates. The UV-Vis transmission spectra of the prepared substrates were investigated. Perovskite solar cells will be fabricated and stability of the devices were encapsulated with copolymer films on the top side and tested under standard ISOS-L-1 protocol and then compared to the commercial unmodified ITO/PET or ITO/PEN substrates. In addition, devices with copolymer films laminated on both sides successfully surviving more than 300 hours upon continuous AM1.5G illumination were demonstrated.
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