Design and fabrication of photonic crystals and diffraction gratings for ultra thin film Si solar cells In this thesis, light trapping schemes based on Photonic Crystals (PCs) and Diffraction Gratings are considered. The goal is to integrate such structures into ultra-thin film silicon photovoltaic solar cells, with a view to improve their conversion efficiency. First, a PCs assisted ultra-thin film crystalline silicon (c-Si) solar cell is designed optimized by using the Finite Different Time Domain (FDTD) approach. An increase over 50% is achieved for the absorption, as integrated over the whole spectral range, by patterning a 2D PCs in the active Si layer. This enhancement is achieved by combining Slow Bloch modes and Fabry-Perot modes. In order to fabricate such solar cells, we developed a process based on Laser Holographic Lithography, Reactive Ion Etching and Inductivity Coupled Plasma etching. We have investigated the influence of the parameters taking part in these processes on the obtained patterns. Finally the optical and electrical properties of the devices have been characterized by our co-workers at IMEC, Belgium. Absorption measurements are in good agreement with the theoretical simulations. Moreover, the integrated absorption is tolerant with regard to the sunlight angle of incidence. The final fabricated 2D PCs patterned solar cell exhibits a 20% higher short circuit current (Jsc = 15mA/cm2) than the reference. Additionally, a more complex thin film c-Si solar cells integrating front and back diffraction gratings has been designed. Long wavelength absorption is increased thanks to the long period (750 nm) back grating, while the incident light reflection is reduced by using a short period (250 nm) front grating. A short-circuit current increase up to 30 mA/cm² is predicted for this device, far above the 18 mA/cm² value for the unpatterned reference These are first steps towards the development of a future generation of PC and diffraction grating assisted solar cells.
