In this paper, we present the integration of combined front and back 1D and 2D diffraction gratings with different periods, within thin film photovoltaic solar cells based on crystalline silicon layers. The grating structures have been designed considering both the need for incident light absorption enhancement and the technological feasibility. 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. The simulated short circuit current in a solar cell combining a front and a back grating structures with a 1.2 µm thick c-Si layer, together with the back electrode and TCO layers, is increased up to 30.3 mA/cm², compared to 18.4 mA/cm² for a reference stack, as simulated using the AM1.5G solar spectrum intensity distribution from 300 nm to 1100 nm, and under normal incidence.

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The positive effects of various perturbations introduced in a bidimensional photonic crystal patterned membrane on its integrated absorption are investigated numerically and theoretically. Two phenomena responsible for the enhanced absorption observed are identified: an increase of the spectral density of modes, obtained thanks to folding mechanisms in the reciprocal lattice, and a better coupling of the modes with the incident light. By introducing a proper pseudo-disordered pattern, we show that those two effects can be exploited so as to overcome the integrated absorption obtained for an optimized and single pattern unit cell Photonic Crystal.http://link.aps.org/