Quaternary phosphonium salts as cationic selective dispersants in silver conductive pastes for photovoltaic applications

Abstract

Over a dozen novel cationic phosphonium dispersants were used in preparation of conductive silver pastes for photovoltaic applications. We investigated the relationship between the structures of phosphonium compounds and the efficiency of p-type silicon PV cells and the phosphorus interaction with the wafer, frit, and silver particles in the paste. Three dispersants were found to be the most beneficial with increases in the cell efficiencies of 0.1–0.3% on poly-crystalline and mono-crystalline Si cells. All of them have long chain substituents at phosphonium function and weakly coordinating anions. Better dispersion of metal oxide particles, which are making the frit, was seen when these phosphonium dispersants are present. Laser ablation – ICP-MS was used to measure the phosphorus profile, and was able to detect phosphorus within silver particles and the silicon substrate indicating the possibility of self-doping. Additionally, the transmission line method (TLM) was applied to quantify the contact resistivity.