Detailed analysis of annealing silver front side contacts on silicon solar cells

New concepts for high efficient solar cells require a post processing annealing step for passivation quality improvement. For cutting costs, thick film metallization is used for the front side. In this paper annealing steps of different duration and temperature are applied to standard industrial silicon solar cells to probe the sensitivity for such a front side metallization towards annealing. This paper focuses on five minute annealing under nitrogen atmosphere and determines favourable annealing temperatures and metallization pastes. In our investigations I–V curve measurements showed that from a certain threshold onwards, an increasing thermal budget decreases cell´s performance. Series and contact resistance measurements were determined to be significantly affected by annealing. Scanning electron microscopy (SEM) revealed that silver crystallites at the silver silicon interface are transformed in shape for annealing at high temperatures which is most probable the microscopic reason for an increased contact resistance.