Research On Conductive Silver Pastes For Front Electrode Of Crystalline Silicon Solar Cells

Due to the excellent electrical,optical,catalytic and thermal properties,silver powders are widely used in the electronics industry.In particular,micron-sized silver particles play an important role in the preparation of conductive silver pastes used for the front electrodes of crystalline silicon solar cells.Silver paste is a three-phase mixture of silver powders,glass powders and organic carriers.Silver powder is the most important conductive phase.Therefore,higher standards are required to obtain the silver powder of high quality.However,the currently prepared micron-sized spherical silver particles still have problems such as poor repeatability,low sphericity,and uneven particle size.Considering the problems mentioned above this paper proposes a method,which can be used to chemically control the nucleation and growth process of silver particles by using two surfactants to achieve monodisperse silver particles with high sphericity and uniform particle size.Through the investigation of the chemical reaction mechanism and reaction parameters,the size control of the silver particles has been successfully achieved.Subsequently,the prepared silver powder was formulated into a paste,the silver paste ratio with the best printing performance was obtained through the rheological test,and the silver paste was sintered to form a film and tested for its electrical conductivity and adhesion properties.Through a series of experiments,the correlation between the sintering parameters of the silver paste and the performance of the silver film was found.The main conclusions obtained are as follows:1)The preparation of micron silver particles was studied systematically.The morphology control of the silver particles is achieved by controlling the size and morphology of primary particles.Gum arabic is used as an auxiliary reducing agent and carrier,firstly a small amount of silver is reduced by the gum arabic as a seed crystal,then the long chain of gum arabic is used as a carrier for secondary growth.During the secondary growth process,the carboxyl group of anhydrous citric acid chemically adsorbs on the silver surface,causing it to grow into silver nanoplates with a size of about 15 nm.During the assembly process,the long chains of gum arabic make the assembly units(silver nanoplates)of the silver assembly exhibit a certain regularity.With the help of ultraviolet-visible absorption spectroscopy and Fourier infrared absorption spectroscopy,it can be proved that the two surfactants essential for the nucleation and growth of silver particles.Combining the selected area electron diffraction pattern and high-resolution images,it can be observed that the silver nanoplates are single crystal flakes growing along the Ag(100)direction.2)Based on the investigation of mechanism,the preparation parameters of micronsized spherical silver particles is optimized.The size of the prepared micron-sized silver particles is 1.8 μm-4.6 μm,the tap density is 3.787 g/cm3-4.265 g/cm3,and the specific surface area is 1.7273 m2/g-2.6962 m2/g,which meets the requirements of silver powder used in conductive silver paste.3)Through the research on the rheological properties of silver paste,the silver paste formula has been optimized.The ratio of silver powder:glass powder:organic carrier-72:3:25 is determined,the viscosity at a shear rate of 10 s’1 is 20.7 Pa·s,and the shear thinning index is 9.95.4)During the sintering process of silver paste,the larger the size of silver particles,the higher the optimum sintering temperature.The glass phase acts as a binding phase,which diffuses around and carries the silver particles to rearrange in a molten state,forming a dense conductive network.Therefore,it is rational to deduce that the property of the glass melt has a strong relationship with the holding time and heating rate.It is found that the optimized sintering plan for silver paste prepared with 3.8μm silver powder is to set sintering temperature of 900℃,heating rate of 3℃/min,holding time of 10 min,and cooling with the furnace.After curing,the square resistance of the silver film is 4.77 mΩ/□,and the adhesion is 23.5 N.