Study on reducing the contamination of metal impurities for casting silicon ingots by using non-oxide crucible barrier layer

Abstract

This work introduces a novel design of oxide-free and low-cost diffusion barrier layer to reduce the contamination from SiO2 crucible. The diffusion barrier layer consists of two Si3N4 layers and a middle layer of high purity Si powder. The diffusion barrier layer was applied for casting crystalline silicon with different types of seeds and the influence on impurity diffusion in crucible was analyzed. The results show that the diffusion barrier layer could effectively reduce the solid phase diffusion distance of metal impurities from crucible and significantly reduce the low minority carrier lifetime region at the bottom and edge of cast crystalline silicon ingot. Meanwhile, the performance of solar cells made of the wafers at the bottom and edge of ingots are obviously improved. Therefore, this non-oxide diffusion barrier layer could significantly improve ingot quality and increase ingot yield in industrial production.