Deeply etched grating structures for enhanced absorption in thin c-Si solar cells

Sub-wavelength periodic structures in crystalline-silicon (c-Si) for solar cell applications can be designed for maximizing optical absorption in thin films. We have investigated optical response of deeply etched c-Si grating structures using rigorous modeling, hemispherical reflectance, one-sun LIV, and internal quantum efficiency measurements. Model calculations predict that almost ∼ 100 % optical absorption can be achieved in subwavelength 2D structures etched to a depth of ∼ 15 μm. Using advanced reactive ion etching techniques, subwavelength deeply etched grating structures have been fabricated and integrated into solar cells. Preliminary one-sun solar cell measurements from ∼ 10-μm 2D period structures have demonstrated short-circuit current enhancement of ∼ 10 mA. The cell efficiencies were poor due to the lack of surface passivation and emitter optimization. Subwavelength grating solar cells failed to provide any performance boost probably due to the lack of surface passivation. Optimization of emitter formation on these types of deeply etched grating surfaces is expected to lead to high-efficiency, thin-film c-Si solar cells.