Effect of Laser Oxidation Patterning of Polysilicon on The Morphology, Passivation, and Efficiency of Selective DS-TOPCon Cells

Laser oxidation is a rapid, scalable, and production-friendly technique for patterning polysilicon to fabricate double-side tunnel-oxide passivated contact (DSTOPCon) solar cells with selective polysilicon contact on the textured front surface. In this work, we studied the change in morphology and metalized and unmetallized passivation quality if polysilicon subjected to nanosecond UV laser-induced oxidation. Using high-resolution microscopy, we observed significant redistribution of polysilicon leading to non-uniformity in thickness in combination with increased recombination in both metalized and unmetallized regions by a factor of ~4. Full area J<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> of passivated textured polysilicon increased from 9 fA.cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> to 36 fA.cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> while metallized J<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> went up from 41 fA.cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> to 180 fA.cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup>. Accounting for 8.1% area coverage of poly fingers and 2.47% for metal-polysilicon contact area, the total J<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> increase due to laser oxidation was only ~5 fA.cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup>. We also fabricated and modeled 23.2% selective DS-TOPCon cells for reference using inkjet patterning of polysilicon. Device modeling showed that incorporating the observed increases in J<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> due to laser patterning decreases the V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> by only 3 mV, resulting in a mere 0.1% loss in cell efficiency. This minimal efficiency loss is justified by the significant advantage of laser patterning in eliminating multiple processing steps, offering a faster, simpler, and more scalable alternative to traditional methods like inkjet resist printing.