Isabelle Rodriguez

Solar energy harvesting in photoelectrochemical solar cells

Here we study different approaches for increasing energy harvesting in titania based photoelectrochemical solar (PES) cells. We study the light harvesting of PES cells when photonic crystal and photonic sponge architectures are used. We also report on the influence of the surface corrugation of the metal electrode on the harvesting of photocarriers in solar cells

Apollony photonic sponge based photoelectrochemical solar cells

We have developed a quasi-fractal colloidal crystal to localize efficiently photons in a very broad optical spectral range; it has been applied to prepare dye sensitized photoelectrochemical solar (PES) cells able to harvest very efficiently photons from the ultraviolet (UV) and the visible (VIS) regions of the solar spectrum.

Layering transitions in colloidal crystal thin films between 1 and 4 monolayers

This paper investigates the sequence of morphological transitions in a nearly hard particle arrangement of colloidal crystals confined in a wedge cell. Earlier studies have shown intermediate particle arrangements (such as the buckling, rhombic, prismatic, and hcp like phases) to account for the drastic changes in the filling fraction values between the triangular and square arrangements. However, to the best of our knowledge, there is no complete description of the transitions between n and n + 1 layers. Here we describe the ordering of the particles for films between 1 and 4 layers. We also present a new intermediate phase hcp(011) to show the transition between n□ → n△ for n > 2 layers.

Fabrication and characterization of colloidal crystal thin films

We present a laboratory experiment that allows undergraduate or graduate students to get introduced to colloidal crystal research concepts in an interesting way. Moreover, such experiments and studies can also be useful in the field of crystallography or solid-state physics. The work concerns the growth of colloidal crystal thin films obtained from the crystallization of a latex colloidal solution in a wedge cell. Depending on the thickness of the sample, microcrystals with different structures and orientation are obtained. Colloidal arrangements are studied by scanning electronic microscopy images of the top and edge views of several areas of the crystals.

Single Crystal Growth of Hybrid Lead Bromide Perovskites Using a Spin-Coating Method

Synthesis and studies of single crystals of hybrid perovskite are important for achieving a better understanding of the optoelectronic phenomena occurring in this material and for improving ongoing applications. Here, we report on the growth of micrometer-size single crystals of methylammonium lead bromide (MAPbBr3) using the spin coating deposition method on a quartz substrate. We studied the influence of the rotation speed and the use of three different additives N-cyclohexyl-2-pyrrolidone, dimethyl sulfoxide, and 4-tert-butylpyridine on the crystal size and shape. The introduction of an additive in the precursor solution is revealed to be very useful for obtaining crystals with well-defined geometries and for decreasing the amount of defects. In this way, high-quality single crystals that sustain optical resonating modes were obtained and characterized by transmittance and photoluminescence measurements.

Magnetic light and forbidden photochemistry: the case of singlet oxygen

Most optical processes occurring in nature are based on the well-known selection rules for optical transitions between electronic levels of atoms, molecules, and solids. Since in most situations the magnetic component of light has a negligible contribution, the dipolar electric approximation is generally assumed. However, this traditional understanding is challenged by nanostructured materials, which interact strongly with light and produce very large enhancements of the magnetic field in their surroundings. Here we report on the magnetic response of different metallic nanostructures and their influence on the spectroscopy of molecular oxygen, a paradigmatic example of dipole-forbidden optical transitions in photochemistry.

7 – Phase transitions in colloidal crystal thin films

Abstract: This chapter reviews the crystal order of colloidal suspensions as hard spheres when confined in wedge type cells with flat walls. This type of cell allows the study of colloidal crystal growth transitions between one and n monolayers.