THE SILVER AND METAL OXIDE COMPOSITE FOR HIGH PERFORMANCE OF FRONT SILVER ELECTRODE WHICH APPLIED BULK SILICON SOLAR CELL

摘要

Solar energy is one of the good solutions for energy and environmental problems because fossil fuel and nuclear power generation cause serious environmental pollution. Photovoltaic (PV) technology and converting efficiency is remarkably progress. Various types of solar cells with high efficiency and low fabrication cost have been developed such as CdTe, Amorphous Si, and CIGS solar cell etc. Although, bulk Silicon based solar cell is still having best converting efficiency. Front Ag paste is the most important materials for High efficiency of the solar cell because front Ag determine omic contact with emitter layer and collect electrons. Recent technology trend of the solar cell is decreasing the emitter doping concentration because lightly doped emitter can lead to lower emitter saturation current density (Joe) and higher blue response with good surface passivation. However, lightly doped emitter has shallow emitter thickness and narrow thermal budget to preventing junction leakage because silver has fast diffusivity even at lower temperature. Regularly, depth of heavy doped emitter which is 45Ω/sq emitter resistance has junction depth of 0.495μm. In case of 100Ω/sq emitter, Junction depth is shallower than 45Ω/sq emitter which is 277μm. Junction leakage reduces the open-circuit voltage (Voc) and fill factor (FF) of the solar cell. To solve this problem, high emitter resistance cells usually manufactured by selective emitter Process. It has selectively deep emitter thickness beneath silver electrode. A lot of selective emitter techniques have been established such as two step diffusion with oxide layer, doping (phosphorous) paste and laser scribing. However, these methods need additional process and chemical wastes. In this study, focus on another approach about high emitter without additional process. We synthesized core-shell type of silver and metal composite with spray pyrolysis using thermal atomizer. Generally, diffusivity of metal oxide is lower than metal. Therefore metal oxide shell prohibits excessive diffusion or migration of Ag to prevent junction leakage.