Investigation on gettering of impurities during phosphorus diffusion in multicrystalline silicon

This work the influence on the gettering efficiency of varying cooling down ramps following a phosphorus-emitter-diffusion in a high-efficiency solar cell process is investigated. A hold-time ramp is applied at low temperature where the emitter sheet resistance remains nearly unchanged and recombination active defects are still mobile. We observed a significant enhancement of the effective minority carrier lifetime measured by the Carrier Density Imaging (CDI) and Quasi Steady State Photoconductance (QSSPC) methods. This improvement is explained by an increased diffusion of metal impurities into the gettering layer and by formation or growth of precipitates due to a lower solubility of impurities in silicon at low temperatures.