Metallic Nano Structures For Light Trapping In Ultra Thin Gaas And Cigs Solar Cells

One of the natural tendencies of photovoltaic technologies is the systematic reduction of the thickness of the solar cells in order to reduce the cost, to save rare or toxic elements or to limit recombination. So far, crystalline thin-film (GaAs) and poly-crystalline (CIGS) technology are reaching optimum conversion efficiency for thicknesses around 1 or 2 microns. Typically, this thickness range does not require new solutions of optical trappings as it is the case for amorphous silicon. However, if we want to reduce these thicknesses by a factor of 10 or even 100 to study new concepts of collections and conversions (GaAs or GaSb) or reduce the use of indium (CIGS), new needs for efficient light absorption are necessary for these technologies. This manuscript is focused on the design, simulation and realization of innovative nanophotonic solutions for future ultra-thin crystalline solar cells.As a first step, we were engaged in an approach at odds with the usual design of solar cells to trap light in a ultra-thin (≤100 nm) layer of material (GaAs, GaSb and CIGS). We propose an array of metal nanostructure placed in front of the cell, transferred on a metal mirror in order to obtain a high, multi-resonant absorption independent of the angle of incidence and polarization. Numerical analysis of the resonant mechanisms involved was conducted as well as the fabrication and optical characterization of demonstrators. The results of this study are motivating for future work on the ultra-thin devices, involving new concepts of collection (ballistic transport) or conversion (hot carrier solar cells).On the other hand, we studied the possibility of integrating a rear gold nanostructured back contact (200-400 nm) in thin CIGS solar cells to potentially increase the current of short circuit and open circuit voltage. We have proposed an innovative process to achieve this structure and the optical trapping for CIGS solar cells. Numerical study, manufacture of demonstrators and first measurements are presented.