Comparison of Boron and Gallium doped p-type Czochralski silicon for photovoltaic application
A set of p-type Czochralski (Cz) silicon materials grown by Shin-Etsu Handotai was used for a comprehensive investigation, including carrier lifetime measurements and fabrication of high-efficiency solar cells at Fraunhofer ISE. The set of different materials consists of gallium and boron doped wafers grown with the Cz method and boron doped wafers grown with the magnetic Czochralski (MCz) method. A clear correlation of the Cz-specific lifetime degradation and the concentration of boron and interstitial oxygen was observed. Thus, gallium-doped wafers with a high concentration of interstitial oxygen of 13·7 ppm showed no degradation. Excellent stable lifetimes of 1098 ?s and 862 ?s were determined for boron-doped MCz wafers and for gallium-doped Cz wafers, respectively. This high lifetime level was maintained or even improved throughout the cell process optimized for Cz silicon and record efficiencies of 22·7% and 22·5% were achieved for boron-doped MCz silicon and gallium-doped Cz silicon, respectively.