Study On Synthesis And Performance Of Front Silver Paste For Solar Cell

Solar energy is the most important one of the renewable energy, and it is a pollution-free, abundant, renewable energy of the future. Therefore, the study and application of solar energy is a main direction in the future of mankind. Silver paste is the key material of mading solar cells, and its ingredient, preparation process has a direct impact on physical and electrical performance of solar cell. Aimming at the frontier of science and technology of the world today, two key ingredients of solar cell silver paste, namely silver powder and organic vehicle, were investagated. Using chemical liquid-phase reduction method, micron/submicron spherical silver powder for solar cell front silver paste application was prepared. And organic vehicle for solar cell front silver paste application was optimized. At the same time, the law of silver powder characteristics parameter and solar cell performance, the relevance between organic vechicle and scree-pinting, electrical performance and the relevance between preparation processes of silver paste with solar cell performance are discovered. The main results are as follows:1. Highly dispersive micron/submicron spherical silver powder for solar cell front silver paste is investigated. And dispersion mechanism of polyvinyl alcohol for preparing silver powder is firstly revealed, namely it is the chemical and physical adsorption, which is a key technology breakthrough of preparing silver powder by the chemical reduction method. We use silver nitrate as raw materials to prepare silver powder, using chemical liquid-phase reduction process. Through single factor experiment and orthogonal designs, we have optimized two processes preparing silver powder for the solar cell front silver paste.For single factor experiment design, eleven factors of influencing granularity, morphology and dispersivity of silver powder are experimented. The desired silver powder is prepared successfully and its law is discovered. The process conditions:ascorbic acid as reduction agent, PVA as disperser, pH=7, disperser usage of8wt%(relativer to the mass of silver nitrate), dipping speed of12.500mL·s-1, stirring speed of200PRM, the concentration of reducion solution of1.177mol·L-1, the concentration of silver nitrate solution of0.294mol·L-1, adding disperser to silver nitrate solution, adding silver nitrate solution to reduction solution, temperature of50℃, a ethanol solution of glyceryl monostearate as posttreatment agent, as-prepared silver powder has good dispersivity, spherical shape, the average particle size of0.81μm, the distribution of0.37～1.04μm, the tap density of4.9g·cm-3. Using ultraviolet and visible spectrum, the disperser mechanism of the preparation of silver powder using polyvinyl alcohol as disperser is suggested firstly, which mechanism is the chemical and physical absorption mechanisms.Using the orthogonal experimental design, six factors and five levels are experimented. The optimal process conditions:silver nitrate solution concentration of0.3mol·L-1, ascorbic acid solution concentration of1.4mol·L-1, gelatin as disperser, the disperser usage of8wt%(relative to the mass of silver nitrate), pH=4, the temperature of50℃. As-prepared silver powder has the nearly spherical shape, good dispersivity,0.36～1.67μm size distribution, average particle size of0.89μm and the tap density of5.4g·cm-3.Silver powders prepared through the above two kinds of processes are all suitable for preparing front silver paste of solar cell. Each of them has its advantage. Silver powder prepared by the former process has good dispersion while the one prepared by the latter process has high tap density.2. For the first time, a significant impact of dispersivity, tap density of silver powder and silver content in silver paste on the thick film and solar cell has discovered, and a higher dispersivity and tap density of silver powder is conducive to the preparation of the high quality silver paste, and its thick film has good screen-printing, which is helpful to increase conversion efficiency of solar cell (up to17.803%for monocrystalline silicon solar cell). This new discovery has been not reported.3. An optimal organic vehicle formula is found. The solar cell front silver paste prepared using it has desired levelling, thixotropy and screen printing property. And the thick film has bigger wet weight (up to0.18g), thicker thickness (up to33μm) and bigger aspect ratio (up to0.306), and the thick film is even and compact. The grid has high adhesion (up to0.4N/mm2) and good solderability. The cell has higher photo-electric conversion efficiency (up to17.963%). This formula has been not reported.4. This paper for the first time reported that wet silver powder is directly applied to prepare silver paste, which the negative impact of silver powder agglomeration is abated and improve cell efficiency (up to18.020%) by the greatest extent. This process has yet been not seen in reports.5. By improving the preparation process of silver paste, the use of advanced mechanical method in mixxing of solid/liquid and solid/solid and gridding is more even and achieving better performance than the manual methods. At the same time, a significant impact of screen printing, coasting, sintering on the performance is discovered. Only matching the various techniques can high performance be required.