Impact of Acetic Acid Exposure on the Screen-Printed Tellurite-Based Silver Contacts

Degradation due to acetic acid in photovoltaic modules has been a commonly observed phenomenon for both damp-heat exposure and outdoor operations. Acetic acid is formed as a decomposition product of ethylene-vinyl acetate (EVA), a common module encapsulation material. It interacts with the front metallization, causing degradation in the glass layer/metal-silicon interface. This results in the loss of cell performance, contact adhesion, increased resistance, dark areas seen in electroluminescence (EL) imaging, etc. It has been reported that lead oxide (PbO) contained in the glass layer is dissolved by acetic acid causing significant performance losses. To address this issue, robust metallic pastes and new metallization techniques are being developed. However, it is important to assess how these technologies perform in acetic acid environment and withstand degradation before they are implemented in the solar market. In this work, we investigate the impact of acetic acid exposure on novel screen-printable pastes, including a lead-tellurite (Pb-Te-O) based paste and a lead-free tellurite (Te-O) based paste. Solar cells fabricated using these pastes were exposed to acetic acid for different amounts of time. A subset of the cells were also exposed to water to monitor and compare the impact. We measure the change in contact resistivity for the samples by a non-destructive circular transmission line method (cTLM). The contact recombination characteristics are extracted by intensity-dependent photoluminescence imaging and multivariate regression analysis with Griddler AI. Additionally, Suns-V OC measurement was performed to further characterize the cells. Finally, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) were performed to understand the change in materials properties. Our study suggests that both the contact recombination and contact resistivity is affected by exposure to acetic acid. The lead-based paste performs better overall compared to lead-free paste even after different stages of exposure.