Reflection behavior of two-dimensional super-quadratic subwavelength gratings for silicon-based photovoltaics

We theoretically introduce a concept of two-dimensional super-quadratic subwavelength gratings (2D SQSWGs) to further investigate how geometrical shape influences the reflection behavior for biomimetic moth-eye structures, and the outline shape can be controlled by changing the degree of the grating's profile function. Numerical studies on the reflection behavior of the 2D SQSWGs and nanorod gratings reveal that the parabola-shaped grating (degree n=2) with a nearly linear graded index profile has superior antireflection performance, and its average weighted reflectivity (R_ave) is as low as 0.99% under AM1.5 solar illumination. Moreover, research results indicate that the 2D nanocone gratings (n=1) have the best angle-independent optical property. The research findings can be used to guide the design of photovoltaic cells based on biomimetic moth-eye structures, and the concept of 2D SQSWGs can be potentially applied to other photovoltaic and optical devices.