Material limitations due to crucible impurities in multicrystalline silicon for high efficiency solar cells

For the fabrication of high efficiency silicon solar cells, bulk material with low recombination losses is required. Crystal defects and impurities from feedstock and crucible system harm the electrical material quality of multicrystalline silicon wafers. In this work, spatially resolved efficiency losses in multicrystalline silicon are estimated from injection-dependent bulk lifetime measurements, and the impact of decorated crystal defects, dissolved impurities and impurities diffused into the crystallized silicon by solid-state diffusion is quantified. The high-temperature steps of two solar cell processes, a standard PERC process and a high efficiency approach, are applied to two different p-type multicrystalline silicon materials: One block was crystallized in a G1 sized crucible of industrial material quality and the other in a crucible of very pure electrically fused silica. The high purity wafers allow higher efficiencies than the wafers from the standard crucible after both cell processes and profit from a larger efficiency boost achieved by the high efficiency process. An efficiency gain of 0.5% absolute is estimated to be attainable on wafers including a block edge by using a high purity crucible.