Characterization of defects in mono-like silicon wafers and their effects on solar cell efficiency

Cell efficiency distribution of mono-like silicon ingot was investigated. And a long low-efficiency tail was found in the efficiency distribution chart, which degraded the cost-effectiveness of this material. Highly spatial resolved photoluminescence and electron back-scattered diffraction characterizations of the mono-like silicon wafers were performed to investigate the low-efficiency reasons. In the experiments, we found that lots of sub-grains, invisible with naked eyes, formed by low angle grain boundaries and high density of dislocations. Relationship of low angle grain boundaries, dislocations and cell efficiency were also investigated and calculated. It is found that the density of dislocations and low angle grain boundaries increase rapidly in the directional solidification of mono-like silicon ingot. Wafers from the top side of the ingot had high density of dislocations and low angle grain boundaries, which led to low-efficiency cell performance and long low-efficiency tail distribution.