Recombination in ingot cast silicon solar cells

Minority carrier recombination is studied in multicrystalline ingot cast silicon solar cells. The normalized recombination strength Gamma of dislocations is obtained by correlating topograms of the internal quantum efficiency (IQE) with those of the dislocation density rho. Gamma is obtained by fitting an extended theory of Donolato to the experimental data. The measured Gamma-values vary significantly between adjacent dislocation clusters and correlate with the spatial pattern of the dislocations. All Gamma-values are strongly dependent on the parameters of the solar cell process. The influence of phosphorus diffusion and hydrogenation is shown. After solidification of the silicon, impurities from the crucible enter the ingot and deteriorate its border regions during cooling to room temperature. These deteriorated border regions can be significantly improved by an additional low temperature anneal that is applied after phosphorus diffusion. The experiments indicate that the mechanism of the anneal is external phosphorus gettering into the emitter.