Recombination at Metal-Emitter Interfaces of Front Contact Technologies for Highly Efficient Silicon Solar Cells

We present an experimental approach to extract the dark saturation current density j0e-met at the emitter-metal interface of the front contact. For this purpose, 2×2 cm2 sized silicon solar cells have been realized featuring different metallization fractions FM. By simply applying the one-diode-model, the dark current density j01 is determined from the open circuit voltage Voc. From the slope of the j01 over FM plot, j0e-met is extracted. However, this is only valid if the dominant recombination mechanism at Voc features a diode character that is close to unity. Hence, the local ideality factor m is determined from the suns-Voc-curve indicating the required value close to one. Three main effects are observed. First, the metallization methods which are compared show different influences on j0e-met on the same emitter configuration. Second, an emitter drive-in due to an additional short thermal oxidation lowers j0e-met. Also, the field-effect passivation of the highly n-doped selective emitter decreases j0e-met effectively. By combining the field effect passivation with a short drive-in step the very low value of j0e-met = 549 fA/cm2 is reported.