Screen printable fire through nickel contacts for silicon solar cells

Abstract

Metallization of crystalline silicon (Si) solar cells is indispensable for reducing the cost while increasing the overall efficiency. Developing alternative materials to the most commonly used screen printed silver (Ag) contacts is a critical factor. Here, in this study, a nickel (Ni) metal paste consisting of Ni metal particles, glass frit and an organic vehicle is fabricated for screen printed Ni contacts. To prevent possible Schottky barrier formation, a graphene layer is placed on the front surface of the Si solar cell between Ni and Si forming a metal-2D-semiconductor structure ensuring the ohmic (or ohmic-like) contacts. It is demonstrated here that the graphene is transferred successfully onto the textured front surface of the cells and G/2D peaks are observed clearly, indicating the good quality of the graphene layer. Constituents of Ni metal paste, glass frit and organic vehicle, are fabricated in concordance with nickel metal powder and mixed to achieve optimal electrical output parameters. The findings suggest that the transition temperature of the glass frit is between 270 °C and 300 °C resulting in around 475 °C softening temperature, which gives excellent etching behavior to the paste. The average contact resistance of the screen printed Ni contacts governed by etching process is measured around 6.9 mΩ cm2. The SEM images of the contacts show a uniform distribution and sintering behavior similar to that of silver counterparts. The light current-voltage measurements read the open circuit voltage of 660 mV, the short circuit density of 39.11 mA/cm2 and the fill factor of 81.4% resulting in around 21% efficiency.