Exceeding 1 ms effective lifetime in High High-Resistivity P-Type Kerfless Multi-crystalline Wafers

Kerfless p-type wafers of varying resistivity are grown with Direct Wafer technology with precise control of dosing the Boron concentration in the melt. At very low Boron concentration, bulk resistivity values ≫100 Ω-cm are achieved and an effective lifetime above 1 ms is measured, corresponding to an estimated bulk lifetime around 2 ms. In contrast to ingot-based wafers, continuous growth using Direct Wafer technology produces a very tight resistivity distribution at any desired target resistivity, without variations caused by zone refining. In addition, the technology enables growth of 3D wafers, e.g. thin wafers with a thick frame that allows to maintain mechanical wafer strength. Thus, Direct Wafer product can be customized for a given solar cell architecture by growing each individual wafer at the optimum bulk resistivity and optimum thickness.