Design and fabrication of a porous prism film for display backlight applications

This study demonstrates a fabrication method of a porous brightness enhancement film (pBEF) that offers brightness enhancement, light diffusion, color shift reduction, and improved thermal stability. During the ultraviolet imprinting and solvent evaporation processes, the nano/submicron-sized air pores are generated within the polymer prism structure, and micropatterns spontaneously form on the prism surface. The inner pores ranging from 30 to 450 nm can effectively scatter light to mitigate color shift, which is caused by multiple internal reflections within the prism structure. The micropatterns have multiple rings formed one around another with 5–15-µm diameter on the prism surface improve visual quality. Moreover, the obtained functions are achieved in a single film solution, obviating the need for using multiple materials, and the fabrication process is relatively simple and fast as it is conducted under ambient conditions. When the pBEF is integrated into a liquid-crystal display backlight, it provides the brightness enhancement performance and comparable viewing angle distribution of a regular BEF combined with an additional diffuser (two films) and increases brightness by ∼8% compared to a bead prism (particle-based BEF). Additionally, it reduces the redshift (Δxy) from 0.1605 to 0.1415. Furthermore, the pBEF exhibits a lower coefficient of thermal expansion than the regular BEF.