论文部分内容阅读
n-type silicon solar cells offer the potential of a very high efficiency,due to the feasibility of high minority carrier recombination lifetime in the silicon wafer.This lifetime benefits from the absence of the boron-oxygen defect,and the lower recombination activity of common metallic impurities.However,this reduction of Boron- and metal-related defects means the impact of other defects could become more noticeable.Recent reports by Sunpower have described that oxygen-induced stacking faults (OiSF) are sometimes visible as ring-like features in PL of high-efficiency n-type cells,and reduce the cell efficiency.In this paper we will discuss OiSF and other typical defects with ring-like distribution ("striations") in n-type Cz ingots.We will show examples of their dependence on cell process and ingot pull parameters.We will illustrate with results of ingot characterisation as well as results of our industrial bifacial n-type cell process,capable of efficiencies well in excess of 19%.n-type ingots will have a larger resistivity gradient than B-doped p-type ingots,due to the difference in dopant segregation coefficients.This should cause a variation of cell parameters.We will however show that the effect on cell efficiency of the larger resistivity gradient can be kept very modest.