Contact resistivity of ECA bonded joints

The replacement of the traditional tin-lead solder to interconnect solar cells by using electrically conductive adhesives (ECAs) has been under study for decades. Proof of concept has been demonstrated by shingling technology among other applications. However, the long-term stability of such innovative interconnection approaches needs further research. In this work, we extrapolate the figure of merit known as contact resistivity to assess the electrical performance of different ECA bonded joints. Our aim is to demonstrate that the Transmission Line Method (TLM) and the End Resistance Method (TLM-CER) are valid techniques to extrapolate the contact resistivity of such bonds. In addition, we study different contact area sizes to determine the proper sample to obtain an ohmic contact. Moreover, since current crowding may lead to non-ohmic contacts, the source current level is also varied. Results show that both TLM and TLM-CER are valid techniques within the criteria proposed. The former tend to be more accurate for larger contact areas (> 0.64 mm2) while the latter for smaller contact areas (< 0.64 mm2). Wider fingers behave in an ohmic way in the range 10−4 – 10−1 A and lead to better TLM plots, where the contact resistance can be easily extrapolated. Contact resistivity for all the samples studied in this work are in the range 0.108 mΩ cm2 up to 5.7 mΩ cm2.