Fabrication of spherical silicon crystals by dropping method and their application to solar cells

Abstract

Spherical Si crystals for solar cell substrates have been successfully fabricated by a dropping method. In the dropping method, melted Si droplets were instilled at normal pressure or in the decompression state (0.5 atm) to control the cooling rate of the spherical Si, dominating crystal quality parameters such as dislocation density in crystal grains. Differences in the crystal quality of the spherical Si crystals were analyzed by surface observation with scanning electron microscopy after Dash etching. Through our baseline process, spherical Si solar cells were fabricated using spherical Si crystals with a diameter of 1 mm fabricated in the decompression state. The current-voltage measurement of the solar cell showed an energy conversion efficiency of 11.1% (short-circuit current density: 24.7mA/cm2, open-circuit voltage: 60ImV, fill factor: 74.6%). These results indicated that spherical Si crystals fabricated by the dropping method have a great potential for the substrate material of high-efficiency and low-cost solar cells. © 2007 The Japan Society of Applied Physics.