Effect of glass frit chemistry on the physical and electrical properties of thick-film Ag contacts for silicon solar cells

The aim of this study is to understand the effect of the glass frit chemistry used in thick-film Ag pastes on the electrical performance of the silicon solar cell. The study focuses on the physical behavior of the glass frit during heat treatment as well as the resulting Ag−Si contact interface structure. We observe that the glass frit transition temperature (T_g) and softening characteristics play a critical role in the contact interface structure. The glass transition temperature also significantly influences the contact ohmicity of the thick-film metal grid. A high glass frit transition temperature generally results in thinner glass regions between the Ag bulk of the grid and the Si emitter. It was found that a glass frit (with high T_g) that crystallizes fast during the firing cycle after etching the silicon nitride and Si emitter results in smaller Ag crystallite precipitation at the contact interface. This results in smaller junction leakage current density (J_o2) and higher open-circuit voltage (V_oc). Using high T_g pastes (with the appropriate Ag powder size), greater than 0.78 fill factors and >17.4% efficiency were achieved on 4 cm² untextured single crystal Si solar cells with 100 Ω/sq emitters.