Different nucleation approaches for production of high-performance multi-crystalline silicon ingots and solar cells

Abstract

Two different process approaches for growing high-performance multi-crystalline silicon (HPM-Si) material for photovoltaic applications are presented. Assisted nucleation was achieved by seeding on fine polycrystalline silicon chunks and on a rough silica crucible bottom, respectively. For each of the two methods industrially sized ingots of 650kg were directionally solidified. Wafers of these ingots and those from conventionally solidified multi-crystalline (mc) silicon ingots were used to produce solar cells on industrial line. Solar cell parameters were analyzed and compared.Both assisted nucleation methods are suitable for industrial growing of HPM-Si ingots. The grain size is more homogeneously distributed resulting in improved material quality. Less dislocation clustering results in higher average conversion efficiency of solar cells compared to those made of conventionally solidified mc-Si material. Moreover, it is also experimentally proven that assisted nucleation procedure is effective for both Siemens polysilicon feedstock and cheaper solar grade silicon. Further improvements of nucleation procedures, which can be used to achieve higher conversion solar cell efficiency and lower product cost, are proposed.