Towards Enhanced Reliability of Busbar-Free IBC Solar Cell Interconnections by Non-Conductive Adhesive Reinforcement

Current crystalline silicon solar cell metallization layouts feature pad busbars and have (compared to total available interconnection ribbon area) a reduced available surface for soldering or gluing the narrow copper ribbons (rectangular cross section) or wires (round cross section). For further reduction of silver consumption, an emerging trend implies omitting totally the busbars from cell’s metallization, which means that (usually silver-plated) interconnection copper tracks are bonded directly to cell’s fingers and SixNy coated surface [1]. At interdigitated back contact (IBC) solar cell ZEBRA [2], the thermo-mechanical stress during and after interconnection process is higher than for front-back contacted solar cells [3]. Removing completely the busbars at this cell type would therefore pose exceptional challenges for a robust stable interconnection [4]. One promising approach implies point fixing additionally the connected ribbons to the cell surface by non-conductive adhesive (NCA) pads [5]. In this work, we describe the investigation of ECA formulations as electrical connection, in combination with NCA formulations, which will reinforce mechanically the interconnection. The reliability of interconnection was investigated at mini-module level by temperature-cycling test (TCT). The goal of this experiment is to shape a cell interconnection process and testing sequence, and to identify suitable ECA-NCA formulations for a technical and economical competitive ECA pad –NCA pad connection procedure for busbar-free IBC ZEBRA solar cells. The process addresses also environmental aspects, since the interconnection is lead-free, and add additional options for cell-ribbon separation [6].