Ultrathin crystalline silicon solar cells by textured triangular grating

Grating structures can effectively enhance the light absorption abilities of solar cells with ultrathin active layer. In this work, a light trapping scheme composed of front surface triangular grating structure, bilayer antireflection coating and Ag back reflector is first designed for a ultrathin c-Si solar cell with a active layer thickness of 12 μm. The geometrical parameters of grating structure are then optimized by a dimensionless absorption enhancement factor. Finally, four methods are adopted to comprehensively evaluate the performances of the optimal grating structure, i.e. the front surface reflectance of external and internal light with different incident angles, intensity distribution of internal diffraction light and photocurrent density. The results show that the reflectance of external light with the incident angle smaller than 45° can be decreased to a level less than 5 %; light absorbed incompletely in a single pass through the active layer can obtain a diffraction angle larger than 38° for TE mode and 50° for TM mode in the c-Si active layer; internal nonzero-order diffraction light reflected by Ag back reflector can achieve a reflectance larger than 80 % at the front surface; the cell photocurrent density can reach 35.12 mA/cm2.