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 Hando tai was used for a comprehensive investigation, including carrier lifetime measurements and fabrication of hi,high-efficiency solar cells at Fraunhofe r ISE. The set of different materials consists of gallium and boron doped w afers grown,with the Cz method and boron doped wafers grown with the magnet ic Czochvalski (MCz) method. A clear correlation of the Cz-specific lifetim e degradation and the concentration of boron and interstitial oxygen was ob served. Thus, gallium-doped wafers with a high concentration of interstitia l oxygen of 13.7 ppm showed no degradation. Excellent stable lifetimes of 1 098 mu s and 862 mu s were determined for boron-doped MCz wafers and for ga llium-doped Cz wafers, respectively. This hi,oh lifetime level was maintain ed or even improved throughout the cell process optimized for Cz silicon an d record efficiencies of 22.7% and 22.5% were achieved for boron-doped MCz silicon and gallium-doped Cz silicon, respectively. Copyright (C) 1999 John Wiley & Sons, Ltd.