Investigation on Effects of the Laser-Enhanced Contact Optimization Process With Ag Paste in a Boron Emitter for n-TOPCon Solar Cell

Abstract

TOPCon solar cell with boron (B)-doped emitters plays an important role in photovoltaic cell technology. However, a major challenge to further improving the metallization-induced recombination and electrical contact of B-doped emitters. Laser-enhanced contact optimization (LECO) technology is one of ideal candidates for reducing the metallization recombination and contact resistivity. In this study, we investigate the influence of LECO technology using special Ag paste with a decreased Pb content on the performance of the metallization-induced recombination (J₀,_metal), contact resistivity (ρ_c), microtopography of the contact, the I–V parameters, and possible conductive mechanisms. The results showed that the linear resistivity is reduced from 3.56 to 2.60 μΩ·cm owing to special Ag paste, and after LECO treatment, it also has lower ρ_c about 0.91 mohm·cm². Both of them have a large contribution to the FF enhancement. Meanwhile, the J_0,metal drops from 500 to 200 fA/cm², which provides a great contribution to the improvement in open-circuit voltage. The efficiency improved by 0.26% absolute to 25.94%, mainly because of the increased open-circuit voltage (V_oc) of 4 mV and a fill factor (FF) of 0.26%. Simulated by COMSOL, the electron concentration rises to 4 × 10¹⁹ cm⁻³ after LECO treatment, which can generate a larger reverse current to provide a melting temperature for the glass frit, increasing the interface glass phase conductivity. The possible current transport mechanism of LECO is current tunneling effect, resulting in the decrease in the metallization recombination. After the optimization of the LECO process with low-corrosion paste, we manufactured industrial-grade TOPCon cells with E_ff, V_oc, J_sc, and FF values as high as 26.5%, 736 mV, 42.1 mA/cm², and 85.5%, respectively.