A Study For Modification Of Front Electrode Silver Paste Of

The demand for high efficiency and low-cost solar cells become more and more urgent with the pressure of the energy and environmental crisis. The present paper focuses on modification of front electrode silver paste of crystalline silicon solar cells, including experiments of adding a low melting point metal, Bi or Sn, to a commercial front electrode silver paste, and investigations into their effect on firing behavior, and the electrode conductivity and contact resistivity of the fired electrode on silicon nitride-coated silicon wafers. A detailed study of the principle and the methodology of the contact resistance measurement have been carried out before that. Furthermore, numerical simulations of solar cell performance have been conducted to understand the effects of the relevant properties involved in the modifications of the frond electrodes.The study shows, An addition of Bismuth (5%wt) leads to a reduction of the optimum firing temperature of the front electrode from800℃to750℃, with a good electrical performance. It resulted in a sheet resistance of6.5mΩ/□and a specific contact resistance about10-4Ω·cm2, as compared to7.2mΩ/□and about10-4Ω·cm2for the original paste fired at850℃. It is suggested that the reason for the beneficial effects from addition of the low melting point metals is presence of liquid phase, which enhances the sintering of silver powders. In particular, the addition of5%wt Bismuth can harmonize the relationship between the amount of silver deposition and the thickness of the glass layer, to improve the contact interface quality. An addition of1%wt tin also can lower down the firing temperature and leads the sheet resistance little affected compare with original paste; the date is7.3mΩ/□fired at750℃. If the addition of tin is more than1%wt, the electrical performance of the front electrode will become bad. It’s because that the effect of a poor conductive properties of the Ag-Sn alloy phase is more than the enhancement of the density improved by adding tin to the the electrical performance. Through numerical simulations by using PC1D, the emitter resistance below the0.14Ω effects Pmax with a linear relationship; the effect of bulk minority carrier lifetime to the solar cell performance decreases with the lifetime increasing; the effect of the back surface recombination velocity is much larger than the front surface to the solar cell performance, when the back surface recombination velocity is below10000cm/s.