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 concentrationof boron and interstitial oxygen was observed. Thus, gallium-doped wafers with a high concentration of interstitial oxygen of 1377 ppm showed no degradation. Excellent stable lifetimes of 1098 mu s and 862 mu s were determined for boron-doped MCz wafers and for gallium-dopedCz wafers, respectively. This high lifetime level was maintained or even improved throughout the cell process optimized for Cz silicon and record efficiencies of 2277% and 2275% were achieved for boron-doped MCz silicon and gallium-doped Cz silicon, respectively. [ABSTRACT FROM AUTHOR]