Attributes of High-Performance Electron Transport Layers for Perovskite Solar Cells on Flexible PET versus on Glass.

Electron transport layers (ETLs) play a fundamental role in perovskite solar cells (PSCs) through charge extraction. Here, we developed flexible PSCs on 12 different kinds of ETLs based on SnO2. We show that ETLs need to be specifically developed for plastic substrates in order to attain 15% efficient flexible cells. Recipes developed for glass substrates do not typically transfer directly. Among all the ETLs, ZnO/SnO2 double layers delivered the highest average power conversion efficiency of 14.6% (best cell 14.8%), 39% higher than that of flexible cells of the same batch based on SnO2-only ETLs. However, the cells with a single ETL made of SnO2 nanoparticles were found to be more stable as well as more efficient and reproducible than SnO2 formed from a liquid precursor (SnO2-LP). We aimed at increasing the understanding of what makes a good ETL on polyethylene terephthalate (PET) substrates. More so than ensuring electron transport (as seen from on-current and series resistance analysis), delivering high shunt resistances (R SH) and lower recombination currents (I off) is key to obtain high efficiency. In fact, R SH of PSCs fabricated on glass was twice as large, and I off was 76% lower in relative terms, on average, than those on PET, indicating considerably better blocking behavior of ETLs on glass, which to a large extent explains the differences in average PCE (+29% in relative terms for glass vs PET) between these two types of devices. Importantly, we also found a clear trend for all ETLs and for different substrates between the wetting behavior of each surface and the final performance of the device, with efficiencies increasing with lower contact angles (ranging between ∼50 and 80°). Better wetting, with average contact angles being lower by 25% on glass versus PET, was conducive to delivering higher-quality layers and interfaces. This cognizance can help further optimize flexible devices and close the efficiency gap that still exists with their glass counterparts.

Fast and facile preparation of nanostructured silicon surfaces for laser desorption/ionization mass spectrometry of small compounds.

RATIONALE: Many important biological processes rely on specific biomarkers (such as metabolites, drugs, proteins or peptides, carbohydrates, lipids, ...) that need to be monitored in various fluids (blood, plasma, urine, cell cultures, tissue homogenates, …). Although mass spectrometry (MS) hyphenated to liquid chromatography (LC) is widely accepted as a 'gold-standard' method for identifying such synthetic chemicals or biological products, their robust fast sensitive detection from complex matrices still constitutes a highly challenging matter. METHODS: In order to circumvent the constraints intrinsic to LC/MS technology in terms of prior sample treatment, analysis time and overall method development to optimize ionization efficiency affecting the detection threshold, we investigated laser desorption/ionization mass spectrometry (LDI-MS) by directly depositing the sample under study onto cheap inert nanostructures made of silicon to perform straightforward sensitive and rapid screening of targeted low mass biomarkers on a conventional MALDI platform. RESULTS: The investigated silicon nanostructures were found to act as very efficient ion-promoting surfaces exhibiting high performance for the detection of different classes of organic compounds, including glutathione, glucose, peptides and antibiotics. Achieving such broad detection was compulsory to develop a SALDI-MS-based pre-screening tool. CONCLUSIONS: The key contribution of the described analytical strategy consists of designing inert surfaces that are fast (minute preparation) and cheap to produce, easy to handle and able to detect small organic compounds in matrix-free LDI-MS prerequisite for biomarkers pre-screening from body fluids without the recourse of any separation step.

MoS2/TiO2/SiNW surface as an effective substrate for LDI-MS detection of glucose and glutathione in real samples.

Here, we report for the first time, the use of molybdenum disulfide/titanium oxide/silicon nanowires (MoS2/TiO2/SiNW) surfaces for SALDI-MS detection as alternative to MALDI-MS method. Silicon nanowires were fabricated by the well-known metal-assisted chemical etching process followed by the deposition of TiO2 by atomic layer deposition. MoS2 deposition was achieved through hydrothermal treatment. The MoS2/TiO2/SiNW substrate has shown high performance for the detection of small compounds of different molecular weights, including glutathione, glucose, amino acids, antibiotics to name a few. All of the tested compounds, in pure or in mixed solutions were successfully detected in positive ion mode. Therefore, we have also attempted quantitative measurements of GSH and glucose in human blood serum.

CdSe nanorod/TiO2 nanoparticle heterojunctions with enhanced solar- and visible-light photocatalytic activity.

CdSe nanorods (NRs) with an average length of ≈120 nm were prepared by a solvothermal process and associated to TiO2 nanoparticles (Aeroxide® P25) by annealing at 300 °C for 1 h. The content of CdSe NRs in CdSe/TiO2 composites was varied from 0.5 to 5 wt %. The CdSe/TiO2 heterostructured materials were characterized by XRD, TEM, SEM, XPS, UV-visible spectroscopy and Raman spectroscopy. TEM images and XRD patterns show that CdSe NRs with wurtzite structure are associated to TiO2 particles. The UV-visible spectra demonstrate that the narrow bandgap of CdSe NRs serves to increase the photoresponse of CdSe/TiO2 composites until ≈725 nm. The CdSe (2 wt %)/TiO2 composite exhibits the highest photocatalytic activity for the degradation of rhodamine B in aqueous solution under simulated sunlight or visible light irradiation. The enhancement in photocatalytic activity likely originates from CdSe sensitization of TiO2 and the heterojunction between these materials which facilitates electron transfer from CdSe to TiO2. Due to its high stability (up to ten reuses without any significant loss in activity), the CdSe/TiO2 heterostructured catalysts show high potential for real water decontamination.

Formation of silicon nanowire packed films from metallurgical-grade silicon powder using a two-step metal-assisted chemical etching method.

In this work, we use a two-step metal-assisted chemical etching method to produce films of silicon nanowires shaped in micrograins from metallurgical-grade polycrystalline silicon powder. The first step is an electroless plating process where the powder was dipped for few minutes in an aqueous solution of silver nitrite and hydrofluoric acid to permit Ag plating of the Si micrograins. During the second step, corresponding to silicon dissolution, we add a small quantity of hydrogen peroxide to the plating solution and we leave the samples to be etched for three various duration (30, 60, and 90 min). We try elucidating the mechanisms leading to the formation of silver clusters and silicon nanowires obtained at the end of the silver plating step and the silver-assisted silicon dissolution step, respectively. Scanning electron microscopy (SEM) micrographs revealed that the processed Si micrograins were covered with densely packed films of self-organized silicon nanowires. Some of these nanowires stand vertically, and some others tilt to the silicon micrograin facets. The thickness of the nanowire films increases from 0.2 to 10 µm with increasing etching time. Based on SEM characterizations, laser scattering estimations, X-ray diffraction (XRD) patterns, and Raman spectroscopy, we present a correlative study dealing with the effect of the silver-assisted etching process on the morphological and structural properties of the processed silicon nanowire films.

Fluorescence spectroscopy and imaging to improve diagnosis of normal and tumoral cytological pancreatic cells.

We investigated a simple and effective diagnostic method for normal and malignant pancreatic cells using fluorescence emission of endogenous and exogenous molecules in cytological cells. Fluorescence imaging was performed to assess the spectral properties and the spatial distribution of the fluorescence emitted by pancreatic cells. The results revealed quite different fluorescence distributions between tumor cells, characterized by perimembrane fluorescence localization, and normal cells exhibiting an intracellular fluorescence. This was not caused by differences in the fluorescence emission of the endogenous fluorophores NAD(P)H or porphyrins but by various localizations of the exogenous molecules (the EA 50 Papanicolaou stain).

Purification of silicon powder by the formation of thin porous layer followed byphoto-thermal annealing.

Porous silicon has been prepared using a vapor-etching based technique on a commercial silicon powder. Strong visible emission was observed in all samples. Obtained silicon powder with a thin porous layer at the surface was subjected to a photo-thermal annealing at different temperatures under oxygen atmosphere followed by a chemical treatment. Inductively coupled plasma atomic emission spectrometry results indicate that silicon purity is improved from 99.1% to 99.994% after annealing at 900°C.

Crystallization of amorphous silicon thin films deposited by PECVD on nickel-metalized porous silicon.

Porous silicon layers were elaborated by electrochemical etching of heavily doped p-type silicon substrates. Metallization of porous silicon was carried out by immersion of substrates in diluted aqueous solution of nickel. Amorphous silicon thin films were deposited by plasma-enhanced chemical vapor deposition on metalized porous layers. Deposited amorphous thin films were crystallized under vacuum at 750°C. Obtained results from structural, optical, and electrical characterizations show that thermal annealing of amorphous silicon deposited on Ni-metalized porous silicon leads to an enhancement in the crystalline quality and physical properties of the silicon thin films. The improvement in the quality of the film is due to the crystallization of the amorphous film during annealing. This simple and easy method can be used to produce silicon thin films with high quality suitable for thin film solar cell applications.