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WPE. Coatings for optical control, photonic applications and solar energy collection

This workpackage points to the development of new families of coatings (single- and multi- layers) requiring a strict control of their optical behaviour. This implies the implementation of mathematical tools to predict and adjust the final characteristics of the films for designed optical properties and applications. It also requires a tailored synthesis of films with a high reproducibility of parameters like refraction index, thickness, layer structure, absorption coefficient, emissivity, etc. This imposes many constrains during the processing of the films. In all cases, the control of microstructure (e.g., porosity of films), nanostructure (e.g., multilayers of nanometric thickness) and composition (e.g., doping of oxide or polymer thin films) are key issues that require the inputs from workpackages A and B. Composite thin films formed by the inclusion of metal nanoparticles within a dielectric matrix are a hot scientific and technological topic with applications as solar absorbent coatings, plasmonic sensors, non-linear optical devices, etc.

An additional development intended within this WP is related to the fabrication of thin films containing dye molecules for photonic applications (e.g., sensors, lasers, etc.) by plasma polymerisation. Applications as sensors and conductive and luminescent films will be targeted here.

E1.
Low emissivity layers on glass panels and polymeric films:
Low emissivity coatings are currently used as decorative layers for architecture panels where the aim goal is to control the flow of heat and radiation in and out through glass windows. These coatings are able to select certain wavelengths of the solar light for an effective control of interior environments, and consist of a multilayer of very thin films of metals (generally some tens nanometres of silver) and oxides (tin and other oxides), with a very precise structure and design

Adhesion problems and stability of the coatings for long time exposure outdoors are key issues that will require of a systematic consideration within this WP. This topic will be mainly pursued by the groups of UMA and UZA-GTF in tight connection with other groups participating in WP’s A-C to effectively solve the many fundamental and application problems that face this technology.
E2.
Transparent and conductive oxides in the form of thin films, used as electrodes on glass and rigid substrates to avoid static charging (coatings of doped SnO2 are currently used in TV monitors for example). FUNCOAT pretends to go a step forward with respect to the state of the art and develop new formulations based on ZnO and other oxides (e.g., oxides of Te) and their preparation on not common substrates as plastics and photovoltaic Si or III-V solar cells. As for activity E1, adhesion and stability problems, togeter with the requirement of a high transmission and conductivity are the main shortages for the development of these materials.
E3.
Metal-dielectric composite coatings. This type of coatings is being proposed for the last generation of selective absorbent coatings for solar energy collection in thermo-electrical generation. FUNCOAT proposes the study of new formulations and structures for the production of selective absorbent coatings for collection of solar energy in high-T thermal collectors. Here, the objective is to reduce the re-emitted energy in the form of infrared when the devices are at high working temperatures (i.e., around 400 ºC) and for this purpose the control of the nanostructure and distribution of the particles is critical. Metal dielectric composites coatings have also attracted a large interest from basic research because the nanoparticles of noble metals (Ag, Au) forming metal-dielectric composite thin films (SiO2, Al2O3, and other related oxides) can support plasmon structures. E3 is expected to produce composite thin films that can be used efficiently as selective absorbent coatings and plasmon-based sensors.
E4.
Dye polymerized thin films for photonic applications:
As a final application of functionalised plastics, this activity aims at the preparation of fluorescent, conductive and/or semiconductive layers based on dyes and related molecules prepared by plasma polymerization techniques. The purpose is the synthesis of novel photonic films based on polymer dyes with fluorescent properties able to act as photonic sensors (gas sensors, light dosimeters, etc.) and be used for organic photovoltaic cells. Experimental studies and theoretical calculations will be done in parallel.

The internal relationship between the activities/tasks with themselves and with other Work Packages is described in the following picture.

Diagrama WPE