Correlation study of doped layer mid-IR properties to the end-of-line parameters of bifacial PERC solar cells

Rapid and non-contact doped layer characterization using mid-IR reflectance and transmittance measurement is a proven inline monitoring approach commercially used in the production lines. Extending this technique to correlate to the end-of-line cell parameters would be highly beneficial in achieving an optimized line. From this study of 200 bifacial PERC cells batch, the phenomenon of shorter wavelength reflectance (RA) correlating with the diffusion profile, and longer wavelength reflectance (RB) correlating with pyramid size [1] is further reinforced. It was also observed that RA, which is directly related to the emitter sheet resistance, is correlated positively with blue response and negatively with $V_{\text{mpp}}$ . Hence lighter emitters have better blue response and worse metal recombination and contact resistance. A very strong correlation was also observed between the blue and red response to the cell Voc, with the red response having higher correlation and hence Voc mostly attributed to base diffusion length variations.