Void Formation on PERC Solar Cells and Their Impact on the Electrical Cell Parameters Verified by Luminescence and Scanning Acoustic Microscope Measurements

This paper shows a non-destructive and fast characterization of solar cells by applying electroluminescence (EL) and photoluminescence (PL) measurements to investigate the effect on the electrical parameters after locating the voids by scanning acoustic microscopy (SAM). For filled contacts EL and PL measurements correlate well with the resulting values for series resistance (RS) and dark saturation current density (j0): the formed LBSF leads to a good surface passivation (high PL signal intensity, low value for j0) and the eutectic layer ensures a good electrical contact (high EL signal intensity, low value for RS). Voids with a sufficiently thick LBSF show a high PL signal intensity whereas the intensity is significantly reduced for a very thin or completely missing LBSF. Increased values for RS can be explained by the missing eutectic layer. In addition, the electrical connection of the LBSF to the paste can be derived from the value of RS.