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Synthesis of a lead- and particle-free metal-organic Ink for front side metallization of crystalline silicon solar cells
We synthesize and investigate a lead- and particle-free metal-organic ink based on silver salts and various glass components to be used for the front side metallization of crystalline silicon solar cells. This novel metallization ink can be considered as a low-temperature sintering ink, as the silver salt reduces and builds a seed-layer layer at 450-480oC. It can locally open the silicon nitride layer as well as form contact to the phosphorous-doped emitter at the surface. Due to the absence of particles in the ink, aerosol or ink jet printing are the ideal deposition technologies, as clogging of the printer nozzles is avoided. Additionally, as another advantage of particle-free inks, no aggregation occurs, allowing long-term stability and homogeneity. For a sufficient conductivity of the contact lines, plating of nickel and copper is investigated as an additional option for cost reduction. A final stable silver-based particle-free ink was developed consisting of 26 wt% metal content including silver-, bismuth-, and zinc-neodecanoate. Both the bismuth and zinc components are responsible for etching the ARC SiNx layer and have been analyzed separately for ink stability, as well as etching parameters in order to reach the optimum component ratio. The solvents used were xylol and N-Methyl-2-pyrrolidon to ensure solubility of the silver-neodecanoic in the solution as well as enable good printability of the ink.