In thin film solar cells, the surface textures for light trapping is employed to enhance the energy converting efficiency. The propagating wave reflects on the metal surface coated with thin transparent conducting oxide (TCO) material and it scatters from the top TCO layer by total internal reflection. Therefore, in order to improve the energy transform efficiency due to sunlight absorbed in the absorbing layer between the top and the bottom TCO layers, the reflection angle control is required. The design issue of wave direction control is replaced with the optimization problem to maximize the wave flux at an objective domain, which is set to guide the reflection wave direction. This research suggests a texture structure using the topology optimization scheme and the design domain is set on the position of the TCO layer above the back reflector.