HfO2 Nanorod Array as High‐Performance and High‐Temperature Antireflective Coating

Abstract

Antireflective (AR) coating with both high antireflectance and omnidirectional characteristic is desired for many advanced optical device applications and photovoltaic thin‐film solar cells. The application of double‐layer antireflective (DLAR) coating to reduce reflectance is largely constrained at wide wavelength range due to refractive index variation within individual layer and between the air–substrate interfaces. In this article, high performance gradient refractive index double‐layer AR coatings with periodically patterned hierarchical porous hafnia nanorods that mimic moth compound eyes are fabricated on a dense hafnia matrix layer using glancing angle deposition technique. The refractive indices for the top and bottom layers of the DLAR hafnia coatings are 1.36 and 1.87. The fabricated films possess high transparency showing zero reflectance at calculated wavelength of 550 nm but also give <1% reflectance over broad range of visible spectrum at different angles of light incidence displaying its omnidirectional characteristic. The shifting and tuning of reflectance to nearly <1% in visible, infrared, and ultraviolet regions was achieved for wide range of substrate materials by tailoring refractive index through porosity and film thickness of the two layers. Moreover, the DLAR hafnia thin films show high thermal stability at high temperatures up to 300 °C.