Shelf life | EPFL Graph Search

Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or no longer on a supermarket shelf (unfit for sale, but not yet unfit for use). It applies to cosmetics, foods and beverages, medical devices, medicines, explosives, pharmaceutical drugs, chemicals, tyres, batteries, and many other perishable items. In some regions, an advisory best before, mandatory use by or freshness date is required on packaged perishable foods. The concept of expiration date is related but legally distinct in some jurisdictions. Background Shelf life is the recommended maximum time for which products or fresh (harvested) produce can be stored, during which the defined quality of a specified proportion of the goods remains acceptable under expected (or specified) conditions of distribution, storage and display. According to the

Compositional Engineering of Perovskite Light Absorbers for Enhanced Stability and Performance through 2D/3D Interfacing

Anwar Qasem M Alanazi

The semiconducting hybrid-organic inorganic halide perovskites have excellent optical and electronic properties that attract the interest of scientists and researchers. Perovskite solar cells have seen the most rising-rate in the chart of solar cell efficiency from 3 to over 25% in less than ten years. In the last three years, most researchers have been focusing on the Î±-FAPbI3-based perovskite solar cells due to having a lower bandgap (1.45 eV) which is closer to the Shockley-Queisser optimum (1.1- 1.4eV) to gain high efficiency. A distinctive feature of FAPbI3 is that it is more thermally stable compared to MAPbI3. However, the Î±-FAPbI3 perovskite is not stable at room temperature as it converts to the undesirable ÎŽ-phase. The 2D- Ruddlesden-Popper-phase-doped 3D FAPbI3 enhancing the stability of the structure, albeit the bandgap is increased rendering a less optimal bandgap. The main achievement of this thesis is discovering that the doping of FAPbI3 with large alkyl ammonium moieties enhances efficiency and stability while maintaining the bandgap of pure Î±-FAPbI3 perovskite phase. I describe the resulting composition by the formula (A)xFAPbI3, where A represents the large alkyl ammonium iodide species. I study the stabilization of Î±-FAPbI3 via doping with 5-amino valeric acid hydroiodide (AVAI). By using solid-state NMR, we demonstrate the atomic-level interaction between this molecular modulator and the perovskite lattice and propose a structural model of the stabilized three-dimensional structure, further aided by density functional theory (DFT) calculations. We find the presence of AVAI produces highly crystalline films with large, micrometer-sized grains and enhanced charge-carrier lifetimes, as probed by transient absorption spectroscopy. Optical measurements confirm that there is no effect on the bandgap of FAPbI3 after doping. The devices based on (AVAI)0.25FAPbI3 exhibit superior operational stability in comparison with neat FAPbI3 while achieving power conversion efficiency of 19%. A similar approach based on benzylammonium iodide (BzI) has been used. The structural and optical characterization of films based on (BzI)xFAPbI3 composition demonstrate that there is no 2D phase forming under these conditions. Moreover, solid-state NMR results show BzI interacting on the atomic level with Î±-FAPbI3 by binding to the 3D perovskite through hydrogen bonding interaction and stabilizing it against the detrimental Î±-to-ÎŽ phase transition. Perovskite solar cells based on the (BzI)0.25FAPbI3composition achieve power conversion efficiencies exceeding 20%, which is accompanied by enhanced shelf-life and operational stability, maintaining 80% of the performance after one year at ambient conditions.Finally, films based on (BzI)0.25FAPbI3 compositions are further investigated upon aging under the ambient conditions, as they show an unexpected transition from black to red color without transition to expected yellow ÎŽ phase, unlike the reference FAPbI3. I perform different measurements to investigate the nature of this red phase as a function of annealing temperature compare these properties to the corresponding Ruddlesden-Popper phase (Bz2FAn-1PbnI3n+1). The red phase was found to be a mixture of a 2D phase (n = 2) Bz2FAPb2I7 and ÎŽ-FAPbI3, which acts as a barrier to the Î±-to-ÎŽ phase transition.

EPFL2021

Characterization of Efficiency and Mechanisms of Cold Atmospheric Pressure Plasma Decontamination of Seeds for Sprout Production

Alexandra Waskow

The consumption of fresh fruit and vegetable products has strongly increased during the past few decades. However, inherent to all minimally processed products is the short shelf life, and the risk of foodborne diseases, which have been increasingly related to such products in many parts of the world. Because of the favorable conditions for the growth of bacteria during the germination of seeds, sprouts are a frequent source for pathogenic bacteria, thus highlighting the need for seed decontamination to reduce the risk of foodborne illness. Consequently, this study focused on cold atmospheric pressure plasma (CAPP) treatment of artificially inoculated seeds in a diffuse coplanar surface barrier discharge to determine the inactivation efficiency for relevant foodborne pathogens and fungal spores. Plasma treatment of seeds resulted in a highly efficient reduction of microorganisms on the seed surface, while preserving the germination properties of seeds, at least for moderate treatment times. To characterize the mechanisms that contribute to microbial inactivation during plasma treatment, an experimental setup was developed to separate ultraviolet light (UV) and other plasma components. The combination of bacterial viability staining with confocal laser scanning microscopy was used to investigate the impact of ozone and other reactive species on the bacterial cells in comparison to UV. Further characterization of the effect of CAPP on bacterial cells by atomic force microscopy imaging of the same Escherichia coli cells before and after treatment revealed an increase in the surface roughness of treated E. coli cells and a decrease in the average height of the cells, which suggests physical damage to the cell envelope. In conclusion, CAPP shows potential for use as a decontamination technology in the production process of sprouts, which may contribute to food safety and prolonged shelf life of the product.

FRONTIERS MEDIA SA2018

Benzylammonium‐Mediated Formamidinium Lead Iodide Perovskite Phase Stabilization for Photovoltaics

Anwar Qasem M Alanazi, Masaud Hassan S Almalki, Felix Thomas Eickemeyer, David Lyndon Emsley, Michael Graetzel, Ulf Anders Hagfeldt, Dominik Józef Kubicki, Jovana Milic, Aditya Mishra, Dan Ren, Zaiwei Wang, Shaik Mohammed Zakeeruddin, Hong Zhang

There is an ongoing surge of interest in the use of formamidinium (FA) lead iodide perovskites in photovoltaics due to their exceptional optoelectronic properties. However, thermodynamic instability of the desired cubic perovskite (α-FAPbI3) phase at ambient conditions leads to the formation of a yellow non-perovskite (δ-FAPbI3) phase that compromises its utility. A stable α-FAPbI3 perovskite phase is achieved by employing benzylammonium iodide (BzI) and the microscopic structure is elucidated by using solid-state NMR spectroscopy and X-ray scattering measurements. Perovskite solar cells based on the FAPbI3(BzI)0.25 composition achieve power conversion efficiencies exceeding 20%, which is accompanied by enhanced shelf-life and operational stability, maintaining 80% of the performance after one year at ambient conditions.