Spherical-chain silica with super-hydrophobic surface and ultra-low refractive index for multi-functional broadband antireflective coatings.

• A double-layer broadband AR coating was designed by the thin film design software (TFCalc™). • The average transmittance of the double-layer AR coating reached 99.64% in the region of 400–800 nm. • The coating exhibits good environmental-resistance and self-cleaning properties. • This broadband antireflective coating holds great potential for use in the field of solar cells. We present a new type of ultra-low refractive index antireflective (AR) coating based on spherical-chain silica particle with super-hydrophobic surface. This AR coating is fabricated using methyltriethoxysilane (MTES) and ethylsilicate (TEOS) as co-precursors to direct silica particles to form a spherical-chain structure. Then hexamethyldisilazane (HMDS) was further used to modify the surface of spherical-chain silica particle, which greatly decreases the refractive index of the silica thin film from 1.139 to 1.098. The formation mechanism of the ultralow refractive index thin film is proposed. The spherical-chain silica particle surface modification with HMDS significantly improves the hydrophobicity of the coated film; the water contact angle of the film increases from 42° to 168°. Ultimately, using this hydrophobic ultralow-index coating as a top-layer, a high-performance double-layer antireflective coating was fabricated with self-cleaning, environmental resistance and a high average transmittance of 99.64% in the wavelength range of 400–800 nm. This multi-functional broadband antireflective coating has potential value in the field of solar cells. [ABSTRACT FROM AUTHOR]