Study On Preparation Of Highly Dispersive Spherical Silver Powders

In order to meet the requirements of miniaturization and integration of electronic component, the market demand of highly dispersive spherical silver powders continue to grow. Meanwhile, extensive studies on the preparation of highly dispersive spherical silver powders have been carried out worldwide. In this work, highly dispersive spherical silver powders were prepared by liquid-phase reduction method with ascorbic acid as reductant. The influences of processing parameter on the particle size and morphology of silver powders were studied. The optimum reaction condition was decided by orthogonal experiments. The application of dispersive spherical silver powders in grid electrode paste for crystalline silicon solar cell was preliminary studied.The influences of pH value of reductive system, concentration of silver nitrate and ascorbic acid, dosage of dispersant and dropping speed on the silver particle size and morphology were studied. The results indicated the particle size increased with the increasing of concentration of silver nitrate and ascorbic acid, decreased with the increasing of dispersant dosage and dropping speed, and increased first and then decreased with the increasing of pH value of reductive system. The process of PVP in the preparation of silver powders was investigated by fourier transform infrared spectrometer and ultraviolet spectrometer. It was found that the process of PVP can be explained as three aspects. The first aspect was the formation of coordinative bonding between PVP and silver ions,the second aspect was the reduction reaction of silver ions was promoted due to PVP, and the third aspect was PVP prohibited grain growth and particle aggregation.The optimum reaction condition was decided by orthogonal experiments. The factors of pH value of reductive system, concentration of silver nitrate, concentration of ascorbic acid and dosage of dispersant were analyzed with particle size as check index. It was found that the optimum reaction condition was concentration of silver nitrate is 0.29mol/L, concentration of ascorbic acid is 0.11mol/L, weight ratio of dispersant to silver nitrate is 0.5, pH value of reductive system is 6. Under this condition, spherical silver powders with average size 1²Î¼m were generated, the size distribution of the silver powders was 0.5⁵μm, the surface area of the silver powders was 0.5¹m²/g, the silver powders tap density was more than 3.5g/cm³ and the silver powders loose density was more than 2.6g/cm³, the liquidity of the silver powders was good.In order to meet the demand of grid electrode paste for crystalline silicon solar cell, SiO₂-B₂O₃-PbO glass was designed and prepared. The softening temperature of the designed glass was 400⁶00℃. The composition of 82⁸5% silver powders, 3% glass powders and 12¹5% organic phase were mixed to prepare grid electrode paste. After screen printing and sintering, the grid electrode was gained. The test results indicated that the sheet resistivity of the grid electrode paste was lower than 2.2mΩ/â–¡, the series resistance of the grid electrode was more than 0.25Ωand the photoelectric transformation efficiency of the solar cell was 2.5%. It was found that the grid electrode paste had good electrical conductivity, but under the object process condition(830℃/2s), the formation of perfect Ag-Si ohmic contacts didn't happened due to the high softening temperature of designed glass, which lead to low photoelectric transformation efficiency of the solar cell.