Evaluating the impact of current-generation screen-printed Ag paste on Si solar cell emitter saturation current density

摘要

Current-generation screen-printed (SP) Ag pastes have shown capability to contact lightly doped Si solar cell emitters displaying low saturation current density (J0e) with high fill factor (FF). However, we have observed that higher firing temperatures are needed to achieve low resistance Ag contact, which may degrade J0e and result in lower open circuit voltage (VOC). Higher firing temperatures have also resulted in rear SP Al film blistering. In order to decouple the effects of front and rear contact formation on cell performance, we present data on the impact of SP Ag contacts on n+ phosphorus (P) emitter J0e for a range of doping densities and firing temperatures. Using a range of Ag coverage areas (Ametal) we extract the J0e under SP Ag (Joe, metai)· We observe that the change in J0e as a function of Ametal (dJ0JdAmetaj) increases as firing temperature increases, indicating increasing J0e,metal. Calculated VOC loss at Ametal = 7%, a typical coverage for SP Ag contacts, cannot fully account for experimental VOC loss, and Al back surface field (Al-BSF) degradation due to high temperature firing was found to dominate VOC losses.