TEOS/silane coupling agent composed double layers structure: A novel super-hydrophilic coating with controllable water contact angle value

The soiling of the photovoltaic (PV) modules' front surfaces decreases the power generation efficiency a lot. In this paper, a novel self-cleaning (super-hydrophilic) glass coating material with double layers' structure is prepared and the synthesis process is simple and low-price. This super-hydrophilic coating barely decreases the transparency of the glass above solar cells in the PV modules. It only reduces about 2.9% of transparency compared with original glass. Briefly, TEOS (Tetraethylorthosilicate) is skillfully utilized as hydrophobic interlayer, connected to the substrate surface and super-hydrophilic layer, whose effective component is a particular silane-coupling agent named as 2-[acetoxy (polyethyleneoxy) propyl] triethoxysilane (abbreviated as SIA). The interlayer has three advantages: firstly, after the TEOS hydrophobic layer is coated, SIA's hydrophobic siloxane terminals assemble toward this layer; secondly, SIA's steric hindrance would decrease obviously because most of the molecules assemble orderly on the interlayer; thirdly, TEOS provides much more grafting sites and more SIA molecules are grafted. Thus, with the increasing TEOS's concentration, the SIA's coating becomes firmer, and the SIA's concentration influences the water contact angle (CA). When it is bigger than 2.5%, the CA is less than 10 and the surface turns to super-hydrophilic. Besides, according to the samples with different SIA's concentration and contact angle value, a fitting curve whose R-2 is higher than 0.95 is made. Based on this, the experimental contact angle value of a surface made from this SIA could be predicted. And the difference between experimental and theoretical contact angle value ranges from 1.11% to 5.88%. (C) 2015 Elsevier Ltd. All rights reserved.