UNDERSTANDING THE MECHANISM OF LIGHT INDUCED PLATING OF SILVER ON SCREEN-PRINTED CONTACTS FOR HIGH SHEET RESISTANCE EMITTERS WITH LOW SURFACE PHOSPHORUS CONCENTRATION

The high contact resistance associated with emitters with low phosphorus surface concentration (N-s) can be reduced by forming gas anneal, short time dip in one percent hydrofluoric acid (HF) or light induced plating (LIP) of silver metal on the screen-printed contacts. In this study, a 6% improvement in fill factor was noted after the cells were annealed in forming gas, or dipped in HF or immersed in LIP solution for a short time. The FGA affect the entire contacts area while the HF and LIP solution penetrates the edges of the grid by similar to 10 mu m. After each treatment, only the contact resistance decreased but the finger resistance remained unchanged. This suggests thinning of glass layer at the edges of the gridlines during HF dip and LIP for short time. However, a combination of HF dip and longtime LIP of Ag produced highest fill factor because of the decrease in contact and gridline resistance. Therefore during the longtime LIP of Ag on screen-printed contacts: the solution thins the glass layer at the edge of the finger before the Ag plates to both Ag crystallites and the gridline. This is supported by the SEM cross section of the gridline, which shows no glass layer at the edges of the plated finger.