Realization of Micropatterned, Narrow Line-Width Ni–Cu–Sn Front Contact Grid Pattern Using Maskless Direct-Write Lithography for Industrial Silicon Solar Cells

An industry-ready strategic process for the fabrication of cost-effective, micropatterned Ni–Cu–Sn front contact metallization has been demonstrated using maskless direct-write lithography, which could effectively reduce the shadow loss and thereby enhance the efficiency of silicon solar cells by increasing the active area. This investigation also addresses the challenging issues in Ni–Cu–Sn metallization, such as adhesion of the seed layer, low-ohmic contact formation, background plating, and cell processing complications. An eco-friendly aluminum paste with a sheet resistivity of 35 mΩ/cm2 has been developed to fabricate the rear contact on silicon solar cells. A front contact metallization grid with an optimal narrow finger width of 20 μm with an interfinger spacing of 1000 μm has been micropatterned using maskless direct-write lithography for the metallization process. To improve the electrical and mechanical properties of the nickel seed layer, the thickness was optimized as ∼100 nm with a contact resistivity of 6.87 μΩ cm2, which exhibited an adhesion strength of 2.5 N/mm. A low ohmic contact intermediate silicide layer has been created at the Ni–Si interface by the rapid thermal annealing process at 420 °C for 90 s with subsequent copper and tin electroplating to form the Ni–Cu–Sn contacts. An average cell efficiency of 18.5% is achieved for silicon solar cells with a micropatterned Ni–Cu–Sn-based narrow line-width front contact grid design, which could exhibit an ∼1% cell efficiency enhancement as compared to commercial Ag screen-printed solar cells. An ∼6% improvement in cell performance is achieved by reducing the shadow loss with the Ni–Cu–Sn-based front contact metallization as compared to the commercial Ag screen-printed metallization.