Do hydrogen peroxide mouthwashes have a virucidal effect? A systematic review.

BACKGROUND: The presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in saliva has alerted health professionals to the possibility of contamination by aerosols generated in a number of procedures. The indication of preoperative mouthwash containing 1% hydrogen peroxide for reducing the viral load of SARS-CoV-2 in saliva prior to oral procedures has been significantly disseminated through several citations and influenced various dental associations in the elaboration of dental care protocols during this pandemic period, including patients admitted to hospital wards and intensive care units. AIM: To Our aim was to perform a systematic review to answer the following question: does hydrogen peroxide mouthwash (at any concentration) have a virucidal effect? METHODS: The Cochrane, LILACS, PubMed, Scopus, and Embase databases were searched by using the following key-words: 'hydrogen peroxide', 'mouthwash', 'mouth rinse', 'rinse', 'oral rinse', 'mouth bath', 'mouth wash', and 'mouth washes'. Reviews, letters to the editor, personal opinions, book chapters, case reports, congress abstracts, studies with animals and studies on mouthwash containing other compounds other than hydrogen peroxide were excluded. FINDINGS: During the initial search 1342 articles were identified on the five electronic databases. After excluding some duplicates, 976 articles remained. Only studies assessing the virucidal effect of hydrogen peroxide mouthwash were selected, regardless of publication date. CONCLUSION: After reading titles and abstracts, no article met the eligibility criteria. In conclusion, there is no scientific evidence supporting the indication of hydrogen peroxide mouthwash for control of the viral load regarding SARS-CoV-2 or any other viruses in saliva.

Honeycomb micro-textures for light trapping in multi-crystalline silicon thin-film solar cells.

The liquid phase crystallization (LPC) of silicon is an emerging technology for fabricating 10 - 20 µm thin multi-crystalline silicon layers on glass. LPC silicon solar cells exhibit similar electronic performance to multi-crystalline wafer-based devices. Due to the reduced absorber thickness, however, effective measures for light trapping have to be taken. We present tailor-made micro-structures for light trapping at the LPC silicon back-side, whereby a nano-imprinted resist layer serves as a three-dimensional etching mask in subsequent reactive ion etching. Contrary to state-of-the-art random pyramid textures produced by wet-chemical etching, this method allows to produce tailor-made textures independent of grain orientation. Differently shaped micro-textures were replicated in LPC silicon. Absorptance and external quantum efficiency of periodic honeycomb patterns and random pyramids were found to be equivalent. Thus, the method enables the potential to further optimize light trapping in LPC silicon solar cells.

Unravelling the low-temperature metastable state in perovskite solar cells by noise spectroscopy.

The hybrid perovskite methylammonium lead iodide CH3NH3PbI3 recently revealed its potential for the manufacturing of low-cost and efficient photovoltaic cells. However, many questions remain unanswered regarding the physics of the charge carrier conduction. In this respect, it is known that two structural phase transitions, occurring at temperatures near 160 and 310 K, could profoundly change the electronic properties of the photovoltaic material, but, up to now, a clear experimental evidence has not been reported. In order to shed light on this topic, the low-temperature phase transition of perovskite solar cells has been thoroughly investigated by using electric noise spectroscopy. Here it is shown that the dynamics of fluctuations detect the existence of a metastable state in a crossover region between the room-temperature tetragonal and the low-temperature orthorhombic phases of the perovskite compound. Besides the presence of a noise peak at this transition, a saturation of the fluctuation amplitudes is observed induced by the external DC current or, equivalently, by light exposure. This noise saturation effect is independent on temperature, and may represent an important aspect to consider for a detailed explanation of the mechanisms of operation in perovskite solar cells.

Sinusoidal nanotextures for light management in silicon thin-film solar cells.

Recent progresses in liquid phase crystallization enabled the fabrication of thin wafer quality crystalline silicon layers on low-cost glass substrates enabling conversion efficiencies up to 12.1%. Because of its indirect band gap, a thin silicon absorber layer demands for efficient measures for light management. However, the combination of high quality crystalline silicon and light trapping structures is still a critical issue. Here, we implement hexagonal 750 nm pitched sinusoidal and pillar shaped nanostructures at the sun-facing glass-silicon interface into 10 µm thin liquid phase crystallized silicon thin-film solar cell devices on glass. Both structures are experimentally studied regarding their optical and optoelectronic properties. Reflection losses are reduced over the entire wavelength range outperforming state of the art anti-reflective planar layer systems. In case of the smooth sinusoidal nanostructures these optical achievements are accompanied by an excellent electronic material quality of the silicon absorber layer enabling open circuit voltages above 600 mV and solar cell device performances comparable to the planar reference device. For wavelengths smaller than 400 nm and higher than 700 nm optical achievements are translated into an enhanced quantum efficiency of the solar cell devices. Therefore, sinusoidal nanotextures are a well-balanced compromise between optical enhancement and maintained high electronic silicon material quality which opens a promising route for future optimizations in solar cell designs for silicon thin-film solar cells on glass.

Metastable defect formation at microvoids identified as a source of light-induced degradation in a-Si:H.

Light-induced degradation of hydrogenated amorphous silicon (a-Si:H), known as the Staebler-Wronski effect, has been studied by time-domain pulsed electron-paramagnetic resonance. Electron-spin echo relaxation measurements in the annealed and light-soaked state revealed two types of defects (termed type I and II), which can be discerned by their electron-spin echo relaxation. Type I exhibits a monoexponential decay related to indirect flip-flop processes between dipolar coupled electron spins in defect clusters, while the phase relaxation of type II is dominated by 1H nuclear spin dynamics and is indicative for isolated spins. We propose that defects are either located at internal surfaces of microvoids (type I) or are isolated and uniformly distributed in the bulk (type II). The concentration of both defect type I and II is significantly higher in the light-soaked state compared to the annealed state. Our results indicate that in addition to isolated defects, defects on internal surfaces of microvoids play a role in light-induced degradation of device-quality a-Si:H.

Atomic structure of interface states in silicon heterojunction solar cells.

Combining orientation dependent electrically detected magnetic resonance and g tensor calculations based on density functional theory we assign microscopic structures to paramagnetic states involved in spin-dependent recombination at the interface of hydrogenated amorphous silicon crystalline silicon (a-Si:H/c-Si) heterojunction solar cells. We find that (i) the interface exhibits microscopic roughness, (ii) the electronic structure of the interface defects is mainly determined by c-Si, (iii) we identify the microscopic origin of the conduction band tail state in the a-Si:H layer, and (iv) present a detailed recombination mechanism.

Large-area 2D periodic crystalline silicon nanodome arrays on nanoimprinted glass exhibiting photonic band structure effects.

Two-dimensional silicon nanodome arrays are prepared on large areas up to 50 cm² exhibiting photonic band structure effects in the near-infrared and visible wavelength region by downscaling a recently developed fabrication method based on nanoimprint-patterned glass, high-rate electron-beam evaporation of silicon, self-organized solid phase crystallization and wet-chemical etching. The silicon nanodomes, arranged in square lattice geometry with 300 nm lattice constant, are optically characterized by angular resolved reflection measurements, allowing the partial determination of the photonic band structure. This experimentally determined band structure agrees well with the outcome of three-dimensional optical finite-element simulations. A 16% photonic bandgap is predicted for an optimized geometry of the silicon nanodome arrays. By variation of the duration of the selective etching step, the geometry as well as the optical properties of the periodic silicon nanodome arrays can be controlled systematically.

Cytotoxicity and thermomechanical behavior of biomedical shape-memory polymer networks post-sterilization.

Shape-memory polymers (SMPs) are being increasingly proposed for use in biomedical devices. This paper investigates the cytotoxicity, surface characteristics and thermomechanics of two acrylate-based SMP networks as a function of sterilization using a minimal essential media elution test, FTIR-ATR and dynamic mechanical analysis (DMA). Networks sterilized by low-temperature plasma elicited a cytotoxic response and are shown to completely destroy the cell monolayer. FTIR-ATR analysis showed evidence of surface oxidation with an increase and broadening of the absorbance peak from approximately 3500 to 3100 cm(-1), which is associated with an increase in hydroxyl groups. DMA revealed small, but statistically significant, differences in reduction of the glass transition temperatures of both networks when sterilized with gamma irradiation. One network showed an increase in rubbery modulus, which is an indication of crosslink density, after gamma irradiation. Lastly, practical sterilization concerns of SMP devices are discussed in light of the different methods.