Phosphorous Gettering on Spherical Si Solar Cells Fabricated by Dropping Method

Abstract

Si spheres for spherical Si solar cells are produced by a dropping method. In the current state, the Si spheres are generally multicrystalline. In the dropping method, some impurities, mainly iron, which act as minority carrier recombination centers can be introduced in the Si spheres. To remove the impurities, phosphorous diffusion gettering (P-gettering) has been performed on spherical Si solar cells at 925 °C for 40 min. The effect of P-gettering was evaluated by solar cell performance and external quantum efficiency (EQE). The increase in the EQE of a long wavelength region was confirmed, which indicates that the deleterious impurities in a bulk region (not only the surface region) would be effectively reduced. Also, a minority carrier diffusion length estimated by the surface photovoltage method increased after P-gettering. Consequently, the efficiency of the spherical Si solar cell was improved. These results confirmed that P-gettering is effective to improve the solar cell performance of spherical Si solar cells.