Laser induced forward transfer of high viscosity silver paste on double groove structure

Abstract

Front side metallization is a critical process for the production of solar cells; current research focuses on downsizing finger electrodes and lowering printing costs. Laser-induced forward transfer (LIFT) has the advantages of non-contact and non-mask, which can reduce wafer breakage and silver paste usage during front side metallization. Although LIFT is beneficial in reducing printing costs, it is difficult to further downsize fingers electrodes. In this study, a silicon wafer with a laser-etched double groove structure was adopted as the acceptor to increase the printing resolution of LIFT. During the transfer process, contact between silver paste film and acceptor can only occur in the narrow area between the double grooves. Since the contact area is restricted, the width of the printed line will not exceed the narrow area. This approach improves printing resolution while preserving non-contact and non-mask characteristics. The lines printed have an average width of 30.5 μm and an average aspect ratio of 0.97. Furthermore, the line’s width will not be affected by fluctuations in laser fluence within a specific laser fluence interval. The research with different viscosities revealed four distinct transfer regimes. Through a visual observation system, the donor removal processes of different transfer regimes were observed. The experimental results show that only the sharp-shaped line transfer can achieve high-resolution lines, and the optimal results can be obtained only at a viscosity of 25 Pa·s. Finally, double pulses transfer was adopted to address the issue of excessive line thickness fluctuations.