Preparation And Properties Of Antirefractive Films For Solar Energy Application

Antireflective （AR） films prepared by sol-gel process have been widely used in solarphotovoltaic industry. Generally, films for photovoltaic glass substrate need not only excellentoptical properties, but also good scratching resistance due to the atmospheric conditions. Inthis work, antireflective films with high transmittance and excellent mechanical propertieswere fabricated by sol-gel process.Effects of different preparation techniques on optical and mechanical properties of ARfilms were investigated by UV-VIS-NIR spectrometer, pencil hardness and adhesion test. Theaging time and catalysis condition of the silica sols have found to have significant influenceon the transmission performance and mechanical properties of the films. Base-catalyzed silicafilms can possess high transmittance but poor abrasion-resistance, while acid-catalyzed silicafilms possess low transmittance but good abrasion-resistance. In comparison, acid-catalyzedCTAB/silica films combine the advantages of the acid-catalyzed films and base-catalyzedfilms, possessing high transmittance and good abrasion-resistance.Orthogonal experiment method was used to determine the mole ratio of acid-catalyzedCTAB/silica sols. Effects of CTAB amount and baking time on the properties of the filmshave been investigated. The stability mechanism of CTAB/silica sols was discussed. A bestfilm with maximum light transmittance of99.8%, pencil hardness of5H, and adhesion ofgrade5B was obtained, when molar ratio of TEOS: H₂O: EtOH: HCl: CTAB was1:12:23:0.004:0.2and the baking time was4h.In order to satisfy the integration of film and glass production, the films were pre-heatedat180℃and tempered at720℃. TG-DTA curves and Raman spectrum showed that thetemplate CTAB can be removed completely by tempering, which shortens the baking timeand reinforces the bonding strength between the film and the substrate. The adhesion of thetempered films all reaches5B and their hardness is3H or above. The maximum lighttransmittance of97.7%was obtained which increased about6.0%compared with its glasssubstrate.Making films less susceptible to contamination such as water vapor and volatile organiccompounds, we utilized HMDS as post-treatment agent to modify the surface of the films.The impact of the treatment on the optical properties and weather resistance of the films wasstudied by UV-VIS-NIR spectrometer, water contact angle test and PCT test. The surfacemodification treatment appears to lead to transmittance loss of the films, but improve the hydrophobic property and good weather resistance of the films. The average transmittanceattenuation after pressure cooker test reduced from3.4%to0.7%remarkably, thanks to theimmersion treatment of hexamethyldisiloxane （HMDS） for30min followed by heattreatmentat160℃for3min.