Multilayer anti-reflective coating with ultra-low refractive index SiO2 nanopillars for high efficiency multi-junction GaAs solar cells

The anti-reflective coating (ARC) is an essential component in inverted metamorphic triple-junction gallium arsenide (GaAs) solar cells (IMM-SCs) to improve the light absorption and efficiency. The common approach to realize AR function is to construct a multilayer thin-film with a gradient refractive index (n) change from air to the solar cell. In this study, SiO2 nanopillars (SiO2-NPs) are implemented as the top layer in multilayer thin-films to enhance their broadband anti-reflection capability. The transfer matrix method and electron beam (oblique angle) deposition process are applied for the design and fabrication of the multilayer thin-films, respectively. By optimizing the thickness and n of SiO2-NPs thin-films, an IMM-SC with a SiO2-NPs/Al2O3/TiO2 ARC is achieved with an average reflectivity as low as 5.506% in the 300–1300 nm range. The proposed ARCs have significant implications for the window layer designs of high-performance multi-junction solar cells.