Single-step printing of high-resolution, high-aspect ratio silver lines through laser-induced forward transfer

Abstract

Laser-induced forward transfer (LIFT) has the advantage of the absence of contact and masking, which is beneficial for the front-side metallization of solar cells. However, due to the influence of the interaction between adjacent pulses, it is difficult to obtain continuous lines with a high resolution. In this paper, by optimizing relevant parameters (laser fluence, gap distance, viscosity, spot size, and spot pitch), we demonstrate that silver lines with a high resolution and high aspect ratio (thickness over width) can be printed stably. The printing of single-voxel aims to initially determine the range of parameters necessary to generate high-resolution and high-aspect ratio voxels. Subsequently, based on this parameter range, lines are printed at different spot pitches to define the optimal parameters required to produce continuous lines. A comparison of two different viscosities (250 and 50 Pa·s) reveals that high-resolution continuous lines can only be realized at a viscosity of 50 Pa·s. In addition, the continuous lines printed at a large spot size (150 μm) are more uniform and narrower than those printed at a small spot size (60 μm). Finally, according to the optimal parameters (50 Pa·s viscosity, 150 μm spot size, 30 μm gap distance, 70 μm spot pitch, and 1.3 J/cm2 laser fluence), continuous lines with a 44 μm width and 0.54 aspect ratio are achieved via the single-step printing process.