Solar cell system using a polished concave Si-crystal mirror

We demonstrated a solar cell system comprising a concave-Si-mirror solar cell and a conventional small Si solar cell set at the focal point of the concave-mirror solar cell. The concave-Si-crystal mirror was prepared by mechanically polishing a single-crystal Si wafer. It was used both as a solar cell and mirror. This system can make effective use of the photons reflected from the concave-mirror solar cell because the number of total photons is the sum of photons from both the mirror solar cell and the small solar cell set at the focal point. When the conventional small solar cell with an efficiency of 13.0% was used, the total conversion efficiency of the present system increased to 12.2% compared with the conversion efficiency of 11.5% for only the concave-Si-mirror solar cell. These results show that the present solar cell system has the capability to achieve high efficiency through the effective use of the photons reflected from conventional solar cells.