Broadband Ta2O5 moth-eye antireflection coatings for tandem solar cells on Si

Wafer-scale Ta2O5 moth-eye antireflection coatings are directly patterned on dual junction GaAsP/SiGe solar cells on Si substrates using deep UV photolithography and plasma etching. These sub-wavelength structures have an aspect ratio of 1.2, which results in excellent antireflection properties with an average reflectance of 7% over the entire 400–1100nm. Further optimizations of moth-eye and traditional double layer antireflection coatings (DLARCs) on the device using finite difference time domain (FDTD) method are performed. Optimized moth-eye structures outperform optimized traditional DLARCs with average reflection as low as 2.2% from 400-1100nm.