Influence of periodic texture profile and parameters for enhanced light absorption in amorphous silicon ultra-thin solar cells.

We have investigated the antireflection and light trapping properties of two-dimensional grating arrays in the hexagonal symmetry with various texture morphologies. Optical simulation based on finite-difference time-domain (FDTD) analysis is carried out to understand the role of the structure profile for different periodicities and heights to achieve enhanced light trapping. The considered active medium of interest is 200-nm-thick hydrogenated amorphous silicon. Although the considered texture profiles possess an incremental change of refractive index from incident medium to active medium, a parabolic-shaped front side texture provides better antireflection effects owing to its high diffraction efficiencies in the higher-order modes as compared to other pattern morphologies. In the back side texture, the parabolic-shaped pattern also dominates with better light trapping efficiencies due to its ability to distribute a major amount of diffracted energy in the higher-order modes. The average reflection calculations in the wavelength range of 300-800 nm confirm that in both side textures, a periodicity of 500 nm with a height of 200 nm can be preferentially recommended for less reflection loss and improved scattering in oblique angles. The quantum efficiency calculation verifies that a device designed with these optimized parameters can offer improved efficiency for ultra-thin solar cells.