Alleviating contaminant-induced degradation of TOPCon solar cells with copper plating

Abstract

With the development of silicon (Si) solar cell technology, the tunnel oxide passivated contact (TOPCon) architecture has become the dominant industrial technology in the solar market. At the same time, concerns are raised about the long-term stability of TOPCon photovoltaic modules. The front side metallization of TOPCon solar cells is reported to be susceptible to corrosion as identified during cell and module level damp-heat (DH) testing. In this work, we use copper (Cu) plating on screen-printed (Ag paste with up to 3 % Al) TOPCon solar cells to address this problem. The plated cells show an improved performance due to the higher fill factor, indicating the potential of reducing the silver (Ag) consumption and material cost without sacrificing the solar cell efficiency. NaCl was chosen as a representative contaminant to assess the reliability at the cell level after 6 h of DH. The Cu-plated TOPCon solar cells showed only a ∼11.5% rel drop in efficiency, compared to ∼80% rel reduction in efficiency for the as-received cells. We also show that the Cu plating process results in a considerably denser contact, which hinders the penetration of contaminants. Consequently, the method presented in this work enhances the stability of photovoltaic technology with corrosion-sensitive contacts during field operation, thus contributing to an increase in lifetime and reduction in levelized cost of electricity. • ∼1 μm Cu was plated on the front grid of TOPCon cells with Al-containing front Ag-paste to improve reliability. The increased fill factor enabled ∼0.09% abs higher efficiency of as-plated cells. • Over 80% rel efficiency degradation occurred in non-plated TOPCon cells after 6 hours of DH testing due to increased R s and V oc drop, while plated cells showed only ∼11.5% rel efficiency loss. • Bare cells showed a 10-fold contact resistivity increase after 0.5 hours of DH testing, indicating metal-Si contact corrosion, while plated-Cu retained 1–2 orders lower contact resistivity after 2 hours of DH testing. • SEM and EDS analysis illustrated that plated-Cu can fill the voids of screen-printed contact and make the contact denser, which hinders the contaminant penetration and alleviates contact degradation.

Topics & Concepts