Correlation between the Effectiveness of the Electron-Selective Contact and Photovoltaic Performance of Perovskite Solar Cells.

Metal halide perovskites (MHPs) are mixed electronic-ionic semiconductors with a remarkable photovoltaic potential that has led to a current world record efficiency surpassing 23%. This good performance stems from the combination of excellent light harvesting and relatively slow nonradiative recombination, which are characteristic of MHPs. However, taking advantage of these properties requires electron and hole transport materials that can efficiently extract charge with minimal photovoltage losses and recombination. It is well-known that n-type anatase TiO2 is a good electron-selective contact (ESC), although the fundamental reasons for its functioning are not completely clear to date. In this Letter, we investigate this issue by preparing perovskite-based solar cells with various n-type metal-oxide electron-selective contacts of different chemical nature and crystal structure. Our main finding is that the open-circuit photovoltage remains essentially independent of the nature of the contact for highly selective electron contacts, a fact that we attribute to a recombination rate that is mainly governed by the bulk of the MHPs. In contrast, replacement of the "standard" TiO2 contact by alternative contacts leads to lower short-circuit photocurrents and more pronounced hysteresis, related to enhanced surface recombination at less effective electron-selective contacts.

Carbohydrate source affects the synthesis of silver nanoparticles by Lactobacillus plantarum 1449 and Lactobacillus ruminis 1313.

Strains of Lactobacillus have been used for the synthesis of metallic nanoparticles. Since the carbohydrate source could influence the yield and size of the synthesised nanoparticles, the authors evaluated the potential of Lactobacillus plantarum 1449 and Lactobacillus ruminis 1313 to produce silver nanoparticles (AgNPs) using three carbohydrate sources and AgNO3. The presence of AgNO3 in the medium extended the duration of the acceleration and logarithmic phases of the two strains independently of the carbohydrate source used but did not inhibit their growth. The synthesis of AgNPs started at the second day of culture. In general, the size of the AgNPsranged from 10 to 150 nm; they were smaller and more homogeneous in lactose. In the medium supplemented with glucose, there was a lower production of nanoparticles for both strains. The AgNPs synthesised by L. ruminis 1313 remained enclosed in an extracellular polymeric substance, which probably played an important role in the synthesis of the nanoparticles. The carbohydrate source influenced the yield and size of the AgNPssynthesised by L. plantarum 1449 and L. ruminis 1313; the pH was also important for obtaining nanoparticles of uniform size.

Magnetic field modification of optical magnetic dipoles.

Acting on optical magnetic dipoles opens novel routes to govern light-matter interaction. We demonstrate magnetic field modification of the magnetic dipolar moment characteristic of resonant nanoholes in thin magnetoplasmonic films. This is experimentally shown through the demonstration of the magneto-optical analogue of Babinet's principle, where mirror imaged MO spectral dependencies are obtained for two complementary magnetoplasmonic systems: holes in a perforated metallic layer and a layer of disks on a substrate.

High magneto-optical activity and low optical losses in metal-dielectric Au/Co/Au-SiO(2) magnetoplasmonic nanodisks.

Metal-dielectric Au-Co-SiO(2) magnetoplasmonic nanodisks are found to exhibit large magneto-optical activity and low optical losses. The internal architecture of the nanodisks is such that, in resonant conditions, the electromagnetic field undertakes a particular spatial distribution. This makes it possible to maximize the electromagnetic field at the magneto-optically active layers and minimize it in the other, optically lossy ones.

Probing the electromagnetic field distribution within a metallic nanodisk.

A Co nanolayer is used as a local probe to evaluate the vertical inhomogeneous distribution of the electromagnetic (EM) field within a resonant metallic nanodisk. Taking advantage of the direct relation between the magneto-optical activity and the electromagnetic field intensity in the Co layer, it is shown that the nonuniform EM distribution within the nanodisk under plasmon resonant conditions has maximum values close to the upper and lower flat faces, and a minimum value in the middle.

Longitudinal cutting of pure and doped carbon nanotubes to form graphitic nanoribbons using metal clusters as nanoscalpels.

We report the use of transition metal nanoparticles (Ni or Co) to longitudinally cut open multiwalled carbon nanotubes in order to create graphitic nanoribbons. The process consists of catalytic hydrogenation of carbon, in which the metal particles cut sp(2) hybridized carbon atoms along nanotubes that results in the liberation of hydrocarbon species. Observations reveal the presence of unzipped nanotubes that were cut by the nanoparticles. We also report the presence of partially open carbon nanotubes, which have been predicted to have novel magnetoresistance properties.(1) The nanoribbons produced are typically 15-40 nm wide and 100-500 nm long. This method offers an alternative approach for making graphene nanoribbons, compared to the chemical methods reported recently in the literature.