Rheology Study Of Silver Pastes And Their Application In Screen Printing For Solar Cell Front Side Metallization

An important requirement in processing of front side metallization for solar cells is to print fine lines with a high aspect ratio in mass production. Rheological property of the silver pastes is a key to control printing characteristics and highly related to the cell efficiency. In practice it is however difficult to correlate the aspects of easy printing and non-slumping with commonly used basic paste rheological parameters such as Viscosity and Thixotropic Index. Therefore, to explore the relationship between the rheological properties of the conductive paste and the actual printing, developing simple experimental model for efficient performance evaluation of printing paste is very necessary. The main results from the work of this thesis are as follows:1. We have innovatively synthesized silver powers using the small molecules of succinic acid as dispersant, which has good appearance, uniform particles, good dispersion. And we have optimized the synthesis method. It is applicable to the preparation of the silver paste used in solar cells. In this paper, we optimized the synthesis method. To date, the synthesis method of silver power have not been reported.2. Prepared conductive silver pastes with a simple model system, and examinated their rheological characteristics, with rheological testing methods, such as Flow Ramp, Flow Peak Hold.Studied the effects of adding a small amount of dispersant on the viscosity of the slurry, thixotropy, the stability, using rheological characterization test methods. Experiments showed that a small amount of dispersing agent can produce a significant effect on the slurry viscosity, thixotropy, and the stability of the slurry system can be improved.3. A new rheology characterization method for the silver pastes was developed and applied, using an oscillation rheometry, simulating the paste behavior during screen printing process with a three-stage set-up in a single experiment. The Oscillation Amplitude tests were performed with five commercially available silver pastes for crystalline Si solar cells, and characterized with viscoelastic complex modules(G’ and G”) and respective phase angles at three different stages. The results of screen printing tests on these five pastes with respective solar cell efficiency confirmed that the interpretation of the measured complex modulus and phase angle can effectively predict the pastes performance.