New measurement method for the investigation of space charge region recombination losses induced by the metallization of silicon solar cells
Screen printed silver thick film contacts on the front side of industrial silicon solar cells induce parasitic impurities due to diffusion processes during the high-temperature contact formation process. This leads to space charge region recombination (SCR-recombination) corresponding to efficiency-limiting dark saturation current densities j02. The quantitative determination of j02 via fitting the two diode model to the dark IV curve of the solar cell is subject to errors as the result for j02 strongly depends on individual cell parameters like the series resistance as well as on fit parameters. For detailed studies on the dependency of SCR-recombination on different solar cell process parameters, mainly with focus on the realized front side metallization fraction, a special test structure (front side metallization test pattern) was developed and applied on Cz-Si H-patterned solar cells. With this new measurement method it is possible to vary the metallization fraction over different solar cell groups whereas the series resistance RS is kept nearly constant. This ensures a quantitative evaluation of SCR-recombination. We expect this new measurement method to allow for a more thorough optimization of metallization pastes, emitters and related processes by ensuring a quantitative determination of SCR-recombination. First results with respect to SCR-recombination related fill factor losses are presented.