PhD defense : Multispectral digital diffractive element for smart sunlight concentration for third generation photovoltaic devices

PhD defense : Abbas ALBARAZANCHI

Team : IPP

Title : Multispectral digital diffractive element for smart sunlight concentration for third generation photovoltaic devices

Abstract : The sunlight represents a good candidate for an abundant and clean source of renewable energy. This environmentally friendly energy source can be exploited to provide an answer to the increasing requirement of energy from the world. Several generations of photovoltaic cells have been successively used to convert sunlight directly into electrical energy. The third generation multijunction PV cells are characterized by the highest level of efficiency between all types of PV cells. Optical devices have been used in solar cell systems such as optical concentrators, optical splitters, and hybrid optical devices that achieve Spectrum Splitting and Beam Concentration (SSBC) simultaneously. Recently, the diffractive optical elements (DOE’s) attract more attention for their smart use it in the design of optical devices for PV cells applications.
This thesis was allocated to design a DOE that can achieve the SSBC functions for the benefit of the lateral multijunction PV cells or similar. The desired design DOE's have a subwavelength structure and operate in the far field to implement the target functions (i.e. SSBC). Therefore, some modelling tools have been developed which can be used to simulate the electromagnetic field behavior inside a specific DOE structure, in the range of subwavelength feature. Furthermore, a rigorous hybrid propagator is developed that is based on both the diffraction theories (i.e. rigorous and scalar diffraction theory). The FDTD method was used to model the propagation of the electromagnetic field in the near field, i.e. inside and around a DOE, and the ASM method was used to model rigorously the propagation in the free space far field.
The proposed device required to implement the intended functions is based on two different DOE’s components; a G-Fresnel (i.e. Grating and Fresnel lens), and an off-axis lens. The proposed devices achieve the spectrum splitting for a Vis-NIR range of the solar spectrum into two bands. These two bands can be absorbed and converted into electrical energy by two different PV cells, which are laterally arranged. These devices are able to implement a low concentration factor of “concentrator PV cell systems”. These devices allow also achieving theoretically around 70 % of optical diffraction efficiency for the both separated bands. The impact distance is very small for the devices proposed, which allows the possibility to integrate these devices into compact solar cell systems. The experimental validation of the prototype fabricated appears to provide a good matching of the experimental performance with the theoretical model.

This thesis was supervised by Patrick Meyrueis (University of Strasbourg) and co-diriged by Philippe Gérard (University of Strasbourg) and Pierre Ambs (University of Upper Alsace).

The presentation willl take place on Monday 21 September 2015 at 2.00pm in the amphitheater A207 of the pôle API building in Illkirch.