Thermomechanical-stress-free interconnection of solar cells using a liquid metal

Abstract

Research efforts to overwhelmingly fortify the economics of photovoltaics have focused on increasing the light-to-electricity conversion efficiency and reducing the overall manufacturing costs. Since lowering the consumption of silicon has the potential to greatly curtail the material costs, studies on wafering thin silicon substrates have been performed. However, current methods to interconnect solar cells with metal ribbons are not sufficient to employ thin silicon wafers. Therefore, this study explores a novel route to interconnect solar cells with metal ribbons without thermomechanical stress using a highly conductive liquid metal. Galinstan, which is notoriously difficult to print, is successfully harnessed to be printable by suspending submillimetre-sized Galinstan droplets in the carrier vehicle, as aided by the yield stress. By mechanically sintering the Galinstan paste with gentle mechanical pressure, solar cells are interconnected with metal ribbons at room temperature. Albeit the averaged maximum power of the unit modules interconnected using the Galinstan paste was significantly degraded after just 100 thermal cycles due to the possible formation of resistive intermetallic compounds of Galinstan, the power degradation of the best unit module using the Galinstan paste is −0.9%, which is smaller than the averaged one of the unit modules using a conventional soldering method (-1.35%), implying the thermomechanical-stress-free interconnection method using a liquid metal has a chance to be improved for being a comparable competitor to the conventional soldering method.