Plated contacts for solar cells with superior adhesion strength to screen printed solar cells

Abstract

The improvement of adhesion strength and durability of plated contacts is required for cell manufacturers to gain confidence for large-scale manufacturing. To overcome weak adhesion at the metal/Si interface, new approaches were developed. These involve the formation of laser-ablated anchor points, or grooves in the extreme case of overlapping anchor points, in the heavily doped silicon surface. When plated, these features greatly strengthen the mechanical adhesion strength of the metal. A stylus-based adhesion tester was developed specifically for evaluating the effectiveness of plated contacts to smooth silicon surfaces. The use of such a tester was also extended in this work to textured and roughened surfaces to allow evaluation of different metal contacting approaches. The adhesion strengths for various metal contacting schemes were evaluated, including screenprinted silver contacts, nickel/copper (Ni/Cu) lightinduced plated (LIP) contacts for laser-doped selective emitter (LDSE) cells, buried-contact solar cells (BCSCs), and Ni/Cu LIP contacts formed with laser-ablated anchoring points in selective emitter (LAASE) cells. The latter has superior adhesion strength. The standard “peel test” of the industry was compared to the stylus-based adhesion testing, with the latter shown value for testing metal contacts on smooth surfaces but with caution needed for use with textured or roughened surfaces.