Influence of the medium-temperature light soaking process on the passivation and electronic performance of the N-TOPCon solar cells

Hydrogen (H) passivation is one of ideal candidates to reduce interfacial and bulk defects for providing good passivation by the light soaking process. Herein, we investigate the influence of the medium-temperature light soaking process on the passivation and electronic performance of the N-TOPCon solar cells. The medium-temperature light soaking process had the significant impact on the metallization-induced recombination of the p⁺⁺ layer and the Si substrate with a corroded silver (Ag) at a depth of >165 nm. During the light soaking process, the breaking the bending of (Si:H₂)_n bonds causes H transitions from a bound state in the Si–H bond to a free state. In this state, H captures movable Ag and boron atoms on the wafer's surface for passivation. The mechanism for enhancing the passivation on the metallization-induced recombination under the metal contact (J₀,_metal) of SiO_x/n⁺-poly-Si layer, the emitter dark saturation current density under the passivation layer (J₀) of p⁺ layer, and SiO_x/n⁺-poly-Si layer is to prevent the formation of new defects by removing excess H. An efficiency gain of 0.87 % was observed after the light soaking process, attributed to the increase in open circuit voltage (V_oc), short circuit current density (J_sc), and fill fact (FF) values by 10 mV, 0.15 mA/cm², and 1.5 %, respectively. The partial gain of FF comes from the effect of medium-temperature enhanced metal contact. This research contributes to a profound understanding of the mechanism behind improving the medium-temperature light soaking process improvement and offers a feasible strategy for enhancing the efficiency N-TOPCon solar cells. After optimizing the front surface recombination and the medium-temperature light soaking processes, we manufactured industrial-grade TOPCon cells with in-house efficiency (E_ff), V_oc, J_sc, and FF values as high as 25.8 %, 729 mV, 42.1 mA/cm², and 84 %, respectively.