Light-Induced Degradation in Crystalline Silicon Solar Cells

Abstract

Solar cells manufactured on single-crystalline boron-doped Czochralski-grown silicon (Cz-Si) degrade in efficiency by up to 10% (relative) when exposed to light or minority carriers are injected in the dark until a stable level of performance is reached. This effect, which is now known for 30 years, is due to the activation of a specific metastable defect in the silicon bulk. Although a conclusive explanation of the effect is still to be found, recent investigations have clearly revealed that the metastable defect is correlated with the boron and the oxygen concentration in the material. In block-cast multicrystalline silicon (mc-Si) the same degradation behavior can be observed, but due to the lower oxygen content of mc-Si compared to Cz-Si, the degradation occurs to a lesser extent. The first part of this paper reviews the current status of the physical understanding of the degradation effect and gives an overview of the defect models proposed in the literature. In the second part, an overview of different strategies for avoiding or reducing the degradation is presented.