GaAs-based multi-junction solar cells (MI-SCs) provide a wide solar-energy absorption-band (300-1800 nm), but designing and fabricating a broadband antireflection coating (ARC) are challenging. Because MJ-SCs are typically in a series that connects each subcell, the total output current is limited by the subcell that generates the smallest photocurrent. Thus, the ARC for MI-SCs must be designed not only to obtain broadband absorption but also to minimize light reflection at the wavelength band of the current-limited cell. This study proposes a broadband SiO2/gracled-inclex TiO2 ARC for improving the current-limited subcell performance by using a hybrid deposition (e-beam evaporation and spin-on coating). A bottom TiO2 layer and a top SiO2 layer were deposited through e-beam evaporation, but the middle TiO2 layer was deposited using spin-on coating because the refractive index values of the TiO(2)films could be tuned by applying the spin speed. Therefore, the graded-index TiO2 layers were easily obtained using a hybrid deposition method. In addition, a suitable reflectance spectrum of an ARC structure for a middle-cell current-limited triple-junction (3-J) GaAs solar cell was simulated using commercial optical software. The photovoltaic current-voltage and external quantum efficiency (EQE) were measured and compared. The resulting improvements of a short-circuit current of 32.4% and conversion efficiency of 31.8% were attributed to an enhanced EQE of 32.97% as well as a low broadband reflectance exhibited on the middle cell of the 3-J GaAs solar cell with a SiO2/graded-index TiO2 ARC. (C) 2014 Elsevier BY. All rights reserved.