Correlation between the open-circuit voltage and recombination loss at metal-silicon interfaces of crystalline silicon solar cells

Abstract

For screen-printed silicon solar cells, optimization of the contact characteristics between the front metal electrode and silicon is very significant for realizing high efficiency. As technology advances, the solar cell efficiency has been steadily increased. Especially, as surface recombination becomes more important in high efficiency solar cells, understanding and controlling recombination in the metal contact area are necessary. Recombination at the metal-silicon interface is a major cause of the drop in the open-circuit voltage (Voc) of a solar cell. Thus far, the study of electrodes in silicon solar cells has been largely aimed at reducing the series resistance, and few studies on recombination due to electrodes have been performed. Quantitatively evaluating the recombination in electrodes to assess the effect on the efficiency is expected to become more important in the near future. In this paper, the contact characteristics of a screen-printed silver electrode and silicon interface were analyzed using saturation current density (Jo) measurements according to the surface doping concentration and firing temperature. The effects of the contact characteristics on Voc and recombination were also investigated. Experimental results showed that Jo.pass decreased with decreasing surface doping concentration and Jo.metal increased with increasing surface doping concentration and firing temperature. For quantitative analysis of Jo.metal, the size and distribution of Ag crystallites were observed using SEM and TEM, and the Ag concentration was analyzed by ICP-OES measurements. The larger Jo.metal was, the higher the Ag crystallite concentration, indicating that the Ag crystallites under the electrode increased Jo.metal. The effect of Jo.metal on the electrical characteristics of the solar cell was analyzed by calculating the change in the surface recombination velocity and the decreased width of Voc. Through this study, the recombination in the metallized area, which is expected to become increasingly important, and particularly the effects of the doping profile of the emitter region and silver crystallites on the surface recombination were quantitatively assessed. The amount of silver crystallites on the silicon wafer was quantitatively analyzed.