| Abstract:As one of the main materials for preparing the crystalline silicon solar cell, the conductive silver paste influent the performance of solar cells dramatically. So far, the study of conductive silver paste mainly focuses on front side, while little research is done on the back side. And a lot of key technologies of the back silver paste are in the hands of foreign enterprises or research institutes. Thus it’s of vital importance for us to study the back side silver paste for the crystalline silicon solar cell.In this work, glass frit of the Bi2O3-SiO2-B2O3ternary system and the Bi2O3-SiO2-B2O3-ZnO quaternary system were prepared by the way of traditional melt quenching method. With the method of XRD (X Ray Diffraction), DTA(Differential Thermal Analysis) and IR (infrared spectroscopic analysis), the impacts of composition variation on the softening temperature, crystallization and structure of glass frit were investigated. And with the preparation of conductive silver paste, the effect of glass frit on the performance of thick silver film, as well as the influence of sintering process change on the adhesion force of the back electrode and the cell efficiency were studied. The main results are as follows:(1)In the Bi2O3-SiO2-B2O3ternary system, keeping the content of SiO215%(mole fraction), while Bi2O3between30%-60%(mole fraction), glass is able be formed, but with the increase of Bi2O3,the lower vitrification degree. With the increase of Bi2O3molar ratio, the number of [BiO6] octahedral was increased and the [BiO3] tetrahedron was generated, the [BO4] tetrahedron gradually disappeared and turned into [BO3] triangles, and glass frit softening temperature was gradually reduced.(2)In the Bi2O3-SiO2-B2O3-ZnO quaternary system, with the relative amount of SiO2and B2O3kept invariant, ZnO was used to replace part of the Bi2O3. With the increase of ZnO, the vitrification degree gradually reduced. When the amount of ZnO was quite small, the softening temperature kept invariant. But the stability of glass went down and the crystallization occurred. When the amount of ZnO was15%(mole fraction), the softening temperature had a sudden increase, mainly due to the effect of ZnO. As a glass former, the Zn2+ionic entered the glass network structure as a [ZnO4] tetrahedron to repair the glass network.(3)The effect of glass frit on the back electrode:The addition of ZnO into the glass frit can improve the corrosion resistance of the thick silver film. When the average grain diameter of glass frit is5μm, the glass frit can’t get fully softened, and the thick silver film had more holes. While with2μm the average grain diameter, a compact thick silver film was formed. With the increase of glass frit in conductive silver paste, the adhesion force of the thick silver film firstly increased and then decreased. And the resistance firstly decreased and then increased. When the glass powder content is7%(mass fraction), the comprehensive performance of the thick silver film is the best. And the adhesion force for the thick silver film was4.78N. The resistance rate was1.87mΩ·cm.(4)The effect of sintering process on the back electrode:A too low or too high sintering peak temperature, too short or too long sintering time, is not beneficial to the sinter of cell piece. The best sintering process is: The sintering peak temperature is850℃. The sintering time is120s. The adhesion force of the electrode is4.82N. The conversion efficiency of the cell piece is17.62%. |
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