Hemisphere-shaped silicon crystal wafers obtained by plastic deformation and preparation of their solar cells

Hemisphere-shaped crystal wafers can be prepared by the plastic deformation of Si crystal wafers. To obtain hemispherical Si wafers, graphite convex and concave dies were used. A Si wafer was set between dies and pressed at high temperatures. The Si wafer was pressed by an overweight of 200 N at various temperatures. The deformation regions in which well-shaped (100) and (111) wafers can be obtained by plastic deformation were determined using parameters of thickness and temperature. In order to demonstrate that the shaped wafers are of sufficiently high quality to be used in the preparation of devices, solar cells were fabricated using the hemispherical Si wafers pressed at 1,120°C and 1,200°C. The conversion efficiency of the hemispherical solar cells is 8.5–11.5%. It was clarified from the conversion efficiency of solar cells that the quality of the shaped crystal wafers can be improved by a proper annealing process. Thus, the hemispherical shaped wafers are of high quality to be used in the preparation of devices.