Process-window and morphology prediction in laser-induced forward transfer of high-viscosity silver paste

Laser-induced forward transfer (LIFT) is a promising non-contact technique for transferring high-viscosity silver paste onto silicon wafers for photovoltaic metallization. To predict the stable transfer window and line morphology, a semi-empirical process-window model was established to clarify the effects of laser density, pulse frequency, and scanning speed on silver-paste transfer. Single-point and continuous silver-line transfer experiments were conducted to validate the proposed model. The results show that stable transfer occurs within an energy–density window. Among the tested conditions, a laser density of 6.69 J/cm 2 combined with a pulse frequency of 1400 kHz and a scanning speed of 13 m/s produced continuous and dense silver lines with clear boundaries and the highest aspect ratio. Compared with the flat donor substrate, the micro-grooved donor substrate reduced the average line width by approximately 49.8 % and increased the aspect ratio by about 2.02 times by suppressing lateral paste spreading. Lower pulse frequency or scanning speed led to local thermal damage and sintering, whereas higher pulse frequencies or scanning speeds resulted in insufficient energy input and intermittent lines. This study provides process guidance for process-window and morphology prediction of high-precision, high-density silver electrode lines.