Optimization of Electrically Conductive Adhesive Bonds in Photovoltaic Modules

Abstract

Gluing ribbons to silicon solar cells by using electrically conductive adhesives (ECAs) is an alternative interconnection technology for module integration to the state-of-the-art soldering process. We reveal cost reduction potentials by analyzing the influence of volume and contact resistivity, as well as the bond design of ECAs on the fill factor of photovoltaic modules. Solar cells with structured busbars are considered in the analysis. The volume resistivity is controlled by the cure temperature. We contact individual cells at different curing conditions and measure their fill factors. A volume resistivity of 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> Ω · cm does not cause a significant fill factor reduction compared with an ECA with around 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> Ω · cm. The contact resistivity is varied by using different ribbon coatings. Ag and Sn coatings achieve almost identical fill factors. A bare Cu surface reduces the fill factor. We lower the consumed ECA from 40 to 3 mg/cell by modifying the bond design. A design with 16 mg/cell achieves similar fill factors as with 40 mg/cell. A finite-element model is developed to study the combined influence of electrical properties and the bond design. We propose an optimized contact design for high fill factors and reduced material consumption.