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Light trapping in thin film solar cells: towards the Lambertian limit

In this work we theoretically investigate the light trapping properties of one- and two-dimensional periodic patterns etched in crystalline silicon solar cells with anti-reflection coating and back-reflector, in a wide range of active material thicknesses. The resulting short-circuit current (taken as the figure of merit for efficiency) and the optical spectra are compared with those of an unpatterned cell, and with the ultimate limits to light trapping in the case of a Lambertian (isotropic) scatterer. Photonic patterns are found to give a substantial absorption enhancement, especially for twodimensional patterns and for thinner cells, thanks to physical mechanisms like reduction of reflection losses, diffraction of light into the cell, and coupling into the resonant optical modes of the structure.