High-efficiency n-TOPCon bifacial solar cells with selective poly-Si based passivating contacts.

Improving the conversion efficiency of n-TOPCon solar cell is still a hot topic. The selective poly-Si based passivating contacts (Poly-SEs) are ideal candidates for reducing the parasitic absorption and contact resistivity of n-type silicon solar cells and for providing better current collection. In this work, we used LPCVD and the POCl 3 tube furnace diffusion methods to fabricate the selective poly-Si based passivating contacts, and studied the influences of key process parameters of the SiO x layer formation process (the oxidation duration (t oxidation) and the constant pressure duration (t pressure)), and POCl 3 tube diffusion process parameters (the POCl 3 -N 2 carrier gas flow rate at the deposition, deposition temperature, drive-in temperature) on the n+-poly-Si profiles, recombination current density (J 0), contact resistivity (ρ c) of n-TOPCon solar cells. The results showed that the t oxidation and t pressure had a significant impact on J 0 and ρ c which were mainly related to the distribution number of O and Si4+ content on the growth of the SiO x layer. And the influence of the drive-in temperature of phosphorus (P) diffusion process on J 0 value is stronger than that of the deposition temperature, which was mainly related to the chemical passivation of SiO x layer induced by P-indiffusion into Si at high temperature. The reduction in the thickness of poly-Si from 110 nm to 30 nm led to an increase in the short-circuit current density (J sc) per nanometer of ∼0.0093 mA/cm2 per nm. The Poly-SEs were fabricated by 3D printing mask technology and secondary LPCVD/phosphorus diffusion with J 0, n+ ≈ 5 fA/cm2 (n+-poly-Si layer ≈ 50 nm) and J 0, metal,n++ ≈ 73.8 fA/cm2 (n++-poly-Si layer ≈ 110 nm), and the efficiency was improved by 0.12% owing to the increase in J sc value of 0.28 mA/cm2. After optimizing the passivation process, the industrial-grade TOPCon bifacial cells reached an efficiency (E ff), V oc , J sc , and FF values as high as 25.4%, 721 mV, 42.2 mA/cm2, and 83.5%, respectively. • The SiO x /n+-poly-Si layer induced parasitic absorption encountered in n-TOPCon solar cells. • Selective poly-Si based passivating contacts formed by 3D printing mask technology and secondary LPCVD/phosphorus diffusion. • The key process parameters of the SiO x layer and n+-poly-Si layers were investigated. • Cells with J 0, n+ ≈5 fA/cm2 (50 nm) and J o, metal,n++ ≈73.8 fA/cm2 (110 nm) exhibited the efficiency gain of 0.12%. • A pilot efficiency >25.4% of cells treated with optimized passivation process. [ABSTRACT FROM AUTHOR]