High efficiency triple-junction solar cells employing biomimetic antireflective structures

In this work, we demonstrate a thorough device design, fabrication, characterization, and analysis of biomimetic antireflective structures implemented on a Ga0.5In0.5P/GaAs/Ge triple-junction solar cell. The sub-wavelength structures are fabricated on a silicon nitride passivation layer using polystyrene nanosphere lithography followed by anisotropic etching. The fabricated structures enhance optical transmission in the ultraviolet wavelength range, compared to a conventional single-layer antireflective coating (ARC). The transmission improvement contributes to the enhanced photocurrent, which is also verified by the external quantum efficiency characterization of fabricated solar cells. Under one-sun illumination, the short-circuit current of a cell with a biomimetic structures is enhanced by 24.1% and 2.2% due to much improved optical transmission and current matching, compared to cells without an ARC and with a conventional ARC, respectively. Further optimizations of the biomimetic structures including the periodicity and etching depth are conducted by performing comprehensive calculations based on a rigorous couple-wave analysis method.