A single-material graded refractive index layer for improving the efficiency of III–V triple-junction solar cells

Abstract

We present a single-material titanium oxide (TiO₂) bi-layer antireflection coating (ARC) produced using oblique angle deposition for improving the power conversion efficiency (PCE) of III–V compound semiconductor triple-junction (TJ) solar cells. Experimental demonstration of the porous TiO₂ layers and optical modelling by rigorous coupled-wave analysis indicate that bi-layer TiO₂ could be used as universal ARC for all known TJ stacks with various material combinations. The optimum TiO₂ bi-layer ARC produced on a Ga_0.5In_0.5P/GaAs/Ge TJ solar cell exhibits considerably enhanced PCE of 31.6%, which is higher than that of the cells without ARC (23.8%) and with TiO₂ single-layer ARC (29.1%). Incident angle-dependent device characteristics of the fabricated TJ solar cells are also discussed.