Controllable Synthesis Of Low-cost Silver-coated Copper Conductive Pastes And Their Application In Solar Cells

Front electrodes of traditional solar cells are made of conductive pastes that mainly consist of metal silver.Although metal silver has stable chemical qualities and excellent electrical conductivity,its high price increases the cost of solar cells largely and limits its further application in photo-voltaic industry.By comparison,metal copper has a low cost and a good electrical property,showing great potential in low-cost conductive pastes.Metal copper has a poor oxidation stability,which makes it easy to be oxidized and lose its conductivity.Metal copper is not suitable for conductive pastes directly.By coating the metal copper with a complete and successive silver layer to form a silver-coated copper core-shell structure in this work,we successfully increase the oxidation stability and reduce the cost of conductive pastes at the same time.Firstly,we studied on the coating methods of silver layer and optimized the coating process.After adjusting the proper concentrations,adding order and speed and complexing agents,we successfully obtained a complete and successive coating layer.Results show that the obtained silver-coated copper particles have a standard silver-coated copper core-shell structure.The coating property and the oxidation stability at room temperature are good.The average thickness of coating layer is 75 nm while the average diameter of silver-coated copper?Cu@Ag?particles is about 520 nm.Then,we synthesized conductive pastes by these Cu@Ag particles and further researched on the relationship between the ratio of copper to silver in Cu@Ag particles and the properties of conductive pastes.Results show that Cu@Ag particles with copper to silver=10:1 and 2:1 have a good coating layer and the latter has a thicker coating layer.Cu@Ag particles with different ratios of copper to silver also show different thermal oxidation stability and particles with higher silver concentration tend to have better thermal oxidation stability.Cu@Ag particles with ratio of copper to silver=10:1 begin to oxidize at 198.6°C while Cu@Ag particles with ratio of copper to silver=2:1 begin to oxidize at 236.6°C.Finally,we can come to the conclusion that Cu@Ag particles with copper to silver=10:1 are most suitable for low-temperature very low-cost conductive pastes with electric resistivity of 2.96×10^-2??cm while Cu@Ag particles with ratio of copper to silver=2:1 are most suitable for high-temperature low-cost conductive pastes with electric resistivity of 7.143×10^-5??cm.The efficiency of solar cell with front electrodes made of Cu@Ag particles with copper to silver=2:1 is close to commercial one,indicating a great potential of employing these novel low-cost conductive pastes as the conducive pastes for front electrodes of solar cells.