Multi-crystalline Silicon Casted With The Seed

A large number of impurities and defects, to degrade the minority carrier lifetime,are exited in the multi-crystalline silicon. The unsmooth solid-liquid interface caninfluence on the area where the minority carrier is not uniform, reduces the quality ofthe multi-crystalline silicon.In this paper, the WT-2000instrument was used to measure the minority carrierlifetime of multi-crystalline silicon, the PLI-20D instrument was used to measure thedislocation density of the silicon wafer. Comparing and analyzing the minority carrierlifetime and the dislocation density of the unseed process and the seed process, someconclusions are obtained as following:1. The solid-liquid interface of silicon ingot casted with unseed process is convex,the difference of the minority carrier lifetime between the center and the around of thecrucible is bigger, and the unsmooth solid-liquid interface have a greater impact to thesubsequent growth, the larger fluctuant solid-liquid interface cause the greater changesof the minority carrier lifetime around the area are.2. The solid-liquid interface of the center brick casted by the seed process is moresmoother than by the unseed process, the minority carrier lifetime of each silicon brickincrease, the minority carrier lifetime of the central silicon brick increases from4.44μ sto5.01μ s, increased by0.57μ s; and the minority carrier lifetime of the edge siliconbrick changes from2.81μs to4.76μs, the average residual of the minority carrierlifetime is1.95μ s, the average minority carrier lifetime of the central silicon wafercasted with seed are increased by0.4μ s.3. Comparing the silicon ingots casted by the unseed process and the seed process,the results show that the change curve of the minority carrier lifetime of the unseedprocess is in accordance with the trend of big to small to big, but the change curve ofthe seed process is increased gradually, so the uniformities of the minority carrierlifetime casted by the seed process was higher than by the unseed process. 4. The results of PL show that the dislocation density of the multi-crystallinesilicon can reduce by the seed process, decreased by13%-20%, and the grain sizeincreases about2.12mm.5. The average photoelectric conversion efficiency of the minority carrier lifetimesolar cell casted by the seed process can increase from16.74%to17.20%, improved0.46%.The above results show that the seed process which use the broken silicon wafersas seed in the bottom can increase the minority carrier lifetime of the minority carrierlifetime, improve the quality and increase the photoelectric conversion efficiency.