Optical absorption enhancement in a Si nanohole structure with hexagonal unit cell for solar cell application.

Periodic hexagonal unit cell silicon nanohole (SiNH) structures with different structural dimensions have been fabricated using polystyrene spheres and investigated in terms of their microstructures and optical reflectance. Compared with a planar Si wafer, such structures exhibit much lower reflectance due to the enhanced scattering introduced by the SiNHs. Optical simulation using the finite element method has also been carried out in order to optimize the structural periodicity and hole diameter for maximum light absorption. The optimum structure is found to have a periodicity of 693 nm and hole diameter of 560 nm, and it yields the highest ultimate efficiency of 28.8%.