26.35%-Efficiency and high-bifaciality n-TOPCon solar cells enabled by UV-ps laser-induced selective modification of double-layered SiOx/n+-poly-Si passivating contacts

Abstract

Double-layered SiO_x/n⁺-poly-Si films with laterally modulated thickness applied in TOPCon (Tunnel Oxide Passivated Contact) solar cells can reduce recombination, enhance contact quality and decrease risk of paste burn-through of the passivation layer. We utilized laser-induced modification technology coupled with sodium hydroxide (NaOH) etching to fabricate poly-Si films with laterally modulated thickness. This approach can effectively remove the outer SiO_x/n⁺-poly-Si layer and retain the inner SiO_x/n⁺-poly-Si layer (close to the silicon substrate), and reduce parasitic absorption. As a result, the parasitic absorption of the poly-Si layer reduces while maintaining the passivation of the poly-Si layer. The laser-treated area exhibited a low reverse saturation current density (J₀) of 4.8 fA cm⁻², low metallization-induced recombination (J_0,metal) of approximately 49.42 fA cm⁻², and low contact resistivity (ρ_c) of about 2.1 mΩ cm². Moreover, the increase in short-circuit current density (J_sc) of 0.31 mA cm⁻² resulted in a 0.1% gain in efficiency. As a result, a certified power conversion efficiency of 26.35% is achieved for TOPCon solar cells with a selective n⁺-poly-Si structure, featuring higher current density and bifaciality. Interestingly, the implementation of a selective n⁺-poly-Si structure in an industrial production line demonstrates high efficiency.