Influence of backside surface morphology on passivation and contact characteristics of TOPCON solar cells

Compared with P-PERC cells, the rear tunnel oxide/n + polysilicon passivation contact structure in N-TOPCon cells makes the influence of rear surface morphology more significant. In this work, the effects of different chemical etching methods and weight loss on the surface topography and passivation characteristics and contact resistance of SiOx/n + poly Si passivated contact structures were investigated by finely controlling the etching process. Studies have shown that for textured surfaces, both increasing the roundness of the pyramids (acid polishing) and flattening the pyramids (alkaline polishing) lead to a more uniform SiOx layer, which improves surface passivation. The significant deterioration of the contact resistance of the alkali-polished flat surface may be more due to the influence of the thickness of the tunnel oxide layer and the concentration of trailing P doping in the substrate. Acid polishing preserves the round pyramid structure but removes the sharp pyramid tips, improving contact passivation while ensuring good metal contact. It can better balance the contradiction between passivation characteristics (J0 ∼ 4.73fA/cm2, J0, metal ∼ 67.26fA/cm2, iVoc ∼ 740 mV) and contact characteristics (ρc, B ∼ 1.67mΩcm2), and achieve the highest average cell efficiency (24.05%).