Quantitative Understanding and Implementation of Screen Printed p+ Poly-Si/Oxide Passivated Contact to Enhance the Efficiency of p-PERC Cells

This paper reports on the modeling, optimization, and implementation of p-TOPCon (tunnel oxide passivating contacts) on the rear side of a PERC to enhance its cell efficiency. Local Al-BSF of a traditional PERC was replaced by p+ poly-Si/oxide passivated contact composed of ~15Å thick chemically grown tunnel oxide, capped with 120-250nm thick p+ poly-Si layer grown by LPCVD. Process optimization resulted in full-area un-metallized recombination current density (J
_0b
,
_pass
) of <; 5fA/cm
²
for planar surface, nearly independent of poly-Si thickness in this range. Metallized Jo showed an increase with decreased poly-Si thickness and was found to be 9.6 and 25fA/cm
²
for 250nm and 120nm poly-Si respectively, with 4.6% direct metal-Si contact fraction, suitable for bifacial cells. A 21.4% baseline PERC cell with local BSF was fabricated and characterized to extract the rear side recombination current density (J
_0b
,) of 65fA/cm
²
. Detailed analysis and device simulation showed that by replacing this LBSF with 250nm TOPCon developed in the study should produce a V
_oc
enhancement of 9.2mV, consistent with the observed cell V
_oc
increase of 10mV.