This study concerns the design optimization of thin-film luminescent solar concentrators (TLSCs) based on polymethylmethacrylate (PMMA)/silica nanohybrid films doped with coumarin dyestuffs specialized in coloring plastics. Two designs of TLSCs had been prepared and characterized.The first consists of a transparent nanohybrid layer coated on a fluorescent PMMAsubstrate. The second design is the ordinary configuration in which fluorescent nanohybrid layer is coated on a transparent PMMA substrate. The investigation of the spectral properties and efficiency parameters recommended the best solar energy conversion efficiency for the second design.The outdoor performance of optimized TLSC was also evaluated under clear sky conditions of Riyadh city, and the hourly values of the optical efficiency,