This paper presents the use of nanorods of different sizes, deposited from a chemical solution, as an antireflection layer in copper-zinc-tin selenide (CZTSe) solar cells. With the aid of the nanorods, the surface reflection of the CZTSe solar cells was reduced from 7.76% to 2.97%, and a cell efficiency of 14% was obtained as a result. Omni-directional anti-reflection was verified by the angle-dependent reflection measurements. The nanorod arrays also provided the CZTSe solar cells with a hydrophobic surface, allowing it to exhibit high resistance against humidity during weatherability tests. This shows that the surface passivation brought by the nanorod layer at the surface could effectively extend the lifetime of the CZTSe solar cells. The rate of efficiency decay of the CZTSe solar cells was reduced by 46.85% from that of the device without a nanorod array at the surface, indicating that this surface layer not only provided effective resistance against reflection at the device surface, but also served as a passivation layer and humidity-resistant surface-protection layer.