Monolayer Thin Film of Subwavelength Nanospheres for Antireflection Coatings

Abstract ² Excellentbroadband antireflection(AR) effect from thin films of monolayer silica nanospheres with diameter of ~100nm self-assembled on glass substrates was demonstrated. With a monolayer thin film of silica nanospheres coated on both sides of a glass, we achieved maximum transmittance of ~99% at 560nm. Preliminary result shows that such monolayer thin film could be applied in organic solar cells to enhance the light absorption in the polymer active layer. OPV device with single side nanospheres AR layer has gained an efficiency enhancement of ~8% compared to devices without AR layers. Index Terms ± antireflection, silica nanospheres, OPV. I. I NTRODUCTION Antireflection coatings (ARCs) have important roles in a wide range of industrial applications such as solar cells, buildings, smart phone displays and camera lenses. Especially in solar cell application, ARCs help enhance the conversion efficiency via achieving low reflectance and increasing light coupling into the active layer [1]. Nevertheless, most of the current ARC technologies are based on destructive interference mechanism, which usually require costly vacuum deposition techniques such as plasma-enhanced chemical vapor deposition (PECVD) [2-3], electron-beam (E-beam) evaporation [4], and sputtering [5]. Meanwhile, recent development in nanotechnologies suggest that subwavelength nanostructures, such as nanowires, nanospheres, nanorods, could be used as a potential low cost antireflection materials. These nanostructures, when carefully designed, create a graded refractive index layer between air and the bottom substrate materials which suppress reflection. Optimized refractive index of single AR film was given by the equation [6]: