ZnO Nanostructures as Efficient Antireflection Layers in Solar Cells

TLDR

An efficient antireflection coating can enhance solar cell performance by increasing light coupling. The study investigates solution‑grown ZnO nanostructures as antireflection coatings for silicon solar cells, compares them to conventional single‑layer ARCs, and proposes further performance gains by tuning the bottom ZnO layer thickness and tip tapering. Rigorous coupled‑wave analysis shows that tapered ZnO nanorod arrays act as modified single‑layer ARCs, with tapering providing impedance matching between silicon and air through a gradual reduction of effective refractive index and eliminating interference fringes via air–ZnO interface roughening. ZnO nanorod arrays achieve broadband reflection suppression from 400 to 1200 nm, with a tapered array averaging 10 nm tip diameter reaching a weighted global reflectance of 6.6%, outperforming an optimized silicon nitride single‑layer ARC.

Abstract

An efficient antireflection coating (ARC) can enhance solar cell performance through increased light coupling. Here, we investigate solution-grown ZnO nanostructures as ARCs for Si solar cells and compare them to conventional single layer ARCs. We find that nanoscale morphology, controlled through synthetic chemistry, has a great effect on the macroscopic ARC performance. Compared with a silicon nitride (SiN) single layer ARC, ZnO nanorod arrays display a broadband reflection suppression from 400 to 1200 nm. For a tapered nanorod array with average tip diameter of 10 nm, we achieve a weighted global reflectance of 6.6%, which is superior to an optimized SiN single layer ARC. Calculations using rigorous coupled wave analysis suggest that the tapered nanorod arrays behave like modified single layer ARCs, where the tapering leads to impedance matching between Si and air through a gradual reduction of the effective refractive index away from the surface, resulting in low reflection particularly at longer wavelengths and eliminating interference fringes through roughening of the air−ZnO interface. According to the calculations, we may further improve ARC performance by tailoring the thickness of the bottom fused ZnO layer and through better control of tip tapering.