Spherical antireflection coatings by large-area convective assembly of monolayer silica microspheres

Solution-processed surface textures are highly desirable for antireflection in high-performance cost-effective solar cells. Inorganic spherical surface textures can be formed with monolayers of microscale silica spheres partially immersed into spin-on-glass films. We report here a convective assembly process for the formation of large-area self-assembled monolayers of silica microspheres on glass, quartz, and silicon substrates. The structure of the self-assembled monolayers and their spatial extent are significantly influenced by sphere concentration in the suspension, dispersed suspension volume, solvent, coating plate speed, and wedge angle. Glass substrates up to 150×150 mm² are uniformly coated with monolayers of 2-μm silica spheres. It is found that the spherical coating improves the transmittance of quartz wafer from 89.2% to 92.7% around 400 nm and from 90.8% to 92.5% around 1100 nm, demonstrating its broad-spectrum nature. The spherical structure offers an attractive solution to antireflection in crystalline silicon solar cells, as well as thin-film, quantum dot, organic, and flexible solar cells.