Improvement of photovoltaic characteristics of B-doped Czochralski-Silicon by Ge codoping

概要

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Boron (B)-doped Si solar cell strongly degrades during practical operation which results low minority carrier lifetime (MCL) thereby low efficiency. The effect of Ge codoping on the MCL, light induced degradation (LID) and the formation mechanism of void defects are investigated in B doped CZ-Si[1]. From the lifetime measurement, it was observed that the MCL increases evidently when the Ge concentration increases in the crystal. Moreover, LID experiment shows that the B-doped CZ-Si wafers showed a rapid initial degradation of lifetime under illumination and almost saturated after prolonged illumination. In the case of B and Ge codoped wafers, the initial lifetime degradation was relatively low with high degraded lifetime especially for the heavily Ge(>1x10^<18>cm^<-3>) codoped CZ-Si. Moreover, the flow pattern defect (FPD) density was drastically decreased as the Ge concentration increased in the crystal. The mechanism for the MCL enhancement, LID and FPD suppression was explained based on Ge-vacancy defect formation during post-growth cooling of the ingots.
2013-05-09