Investigation of the synergistic regulation mechanism of levelling and plasticity in front-side silver paste for TOPCon solar cells

The printing quality of silver pastes is critically dependent on their rheological properties, particularly for the front-side fine-grid system of TOPCon solar cells. This study investigates the synergistic optimization of printing quality and rheology in front-side fine-grid silver pastes for TOPCon cells. Employing three-stage shear tests (3ITT) and yield stress measurements, we systematically evaluated the effects of A-type short-chain silicone levellers and B-type polyacrylate levellers, across varying dosages, on the paste's initial viscosity, thixotropy, recovery kinetics, and printed grid morphology. Results demonstrate that incorporating 0.2 wt% silicone leveller (A-S-0.2 system) significantly enhances paste recovery, achieving 87 % recovery at 17 s with t 50  < 1 s. This performance markedly surpasses both the control group and B-series samples, ensuring morphological stability during screen printing and pre-sintering. Continuous production-line printing verification revealed that formulations A-S-0.23 and A-S-0.25 achieved aspect ratios of 28.9 % and 34.2 %, respectively. Consequently, series resistance was reduced by 19.2 %–26.9 %, and conversion efficiency increased from 26.19 % to 26.59 %. Analysis indicates that the leveller achieves a precise "shear-softening–structural-reconstruction" balance by reducing particle surface energy and suppressing viscosity hysteresis, thereby effectively inhibiting lateral spreading and morphology collapse. This work provides essential design concepts and a theoretical foundation for high-precision fine-grid printing and the fabrication of highly efficient TOPCon devices.