Rear Side Gratings For Silicon Solar Cells: Efficiency Enhancement Finally Demonstrated

After more than 20 years of research on rear side gratings for light trapping in solar cells, we have been able to demonstrate enhanced efficiencies for crystalline silicon solar cells with two different grating concepts and solar cell architectures. In both cases planar front sides have been used. With hexagonal sphere gratings and the tunnel oxide passivated contact (TOPCon) concept, a grating induced J(sc) increase of 1.4 mA/cm(2) and an efficiency increase of 0.8% absolute could be achieved. With binary crossed gratings fabricated by a nanoimprint based process chain, a grating induced J(sc) gain of 1.2 mA/cm(2) and an efficiency gain of 0.7% absolute could be achieved.For the binary grating concept, cell thickness variations have also been performed. The increasing importance of the light trapping properties towards low solar cell thicknesses could be confirmed by an enhanced EQE in the long wavelength region (J(sc) increase: 1.6 mA/cm(2) for 150 mu m and 1.8 mA/cm(2) for 100 mu m thick solar cells).The results are in very good agreement with simulations using the OPTOS modeling formalism. OPTOS enables the further analysis and optimization of grating concepts in silicon solar cells and modules. So a grating induced J(sc) gain of 0.8 mA/cm(2) is forecast for solar cells with pyramidal front side texture. On module level, still a grating induced J(sc) gain of 0.6 mA/cm(2) can be expected.