Manufacturing of Compound Parabolic Concentrator Devices Using an Ultra-fine Planing Method for Enhancing Efficiency of a Solar Cell

Various structural patterns are used to control light properties during propagation. In particular, when light is trapped and concentrated onto solar cells, they generate more electricity than without concentration. Since the sun moves continuously, a compound parabolic concentrator (CPC) can enhance the efficiency of solar cells by light-trapping and concentration because a CPC minimizes optical loss by reducing the reflection and the scattering on the surface of solar cells. However, CPC devices are generally expensive to manufacture and are too large in size to be used for applications requiring portability. Here, we developed a novel manufacturing process for a small CPC device and verified the enhanced efficiency of solar cells. Based on ultra-fine planing and injection molding, this process is an efficient method for mass production because it relies on replication. Two metal molds were precisely machined using an ultra-fine planing method with a diamond tool, and a CPC device was accurately manufactured by injection molding at low cost and within one minute. The variation of the specific cutting resistance during machining of the metal molds increased by four times, and the minimum uncut chip thickness decreased from 1.3 to 0.5 μm, which is called a size effect. The finished CPC device exhibited a surface roughness less than 40 nm and showed high optical efficiency in virtue of light-trapping. Finally, the efficiency of a solar cell with the CPC device was enhanced about 10%.