| Summary: | 碩士 === 國立聯合大學 === 材料科學工程學系碩士班 === 104 === Silver front contact pastes using for solar cell consist of silver powders, lead-glass powders and organic vehicle system. The lead glass frit in the silver front contact paste plays a critical role for good adhesion, wetting, and etching during sintering process. Lead glass may cause damage to the environment and human, so there is the motivation amongst the researchers to develop lead-free glass for contact pastes.
In this study, using the SiO2-B2O3-Bi2O3-ZnO glass system was investigated the structure and physical properties of the glass by changing Bi2O3/ZnO ratio. This glass system was studied to replace lead glass in the silver front contact paste. The relation between silver paste and silicon substrate after sintering process were investigated.
FTIR absorption measurements have been performed for SiO2-B2O3-Bi2O3-ZnO glass system. Adding Bi2O3 to glass network, the vibration intensity of [BO3] and [BO4] units decrease, and shifted to low wavenumber. Bi3+ ion has high polarization to form Bi-O bonding and new [BiO6] units that glass transition temperature and softening temperature decreasing. While the density, molar volume, and thermal expansion coefficient of the glasses decreased with increasing Bi2O3 content.
While changed the Bi2O3 content in glass, the glass content in silver front paste, and the sintering temperature by the rapid heat treatment to investigate the relation between silver paste and silicon wafer. Using SEM to observe the microstructure, glass was softened in the high temperature that would enable wetting and adhesion between silver paste and silicon wafer. Increasing Bi2O3 content of glass has lower softening temperature that is helpful to sintering. The molten glass can dissolve the amount of silver powder and increase the number of Ag-Bi solid solution precipitation in the cooling process.Therefore, it can decrease the resistivity. While increasing sintering temperature and content of glass promote to increase the precipitation of Ag-Bi solid solution to precipitate and decrease the resistivity.
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