Study of pinhole conductivity at passivated carrier-selected contacts of silicon solar cells

High-efficiency solar cells are closing the gap to the theoretical efficiency limit by implementing passivated carrier-selective contacts. This work presents a study on charge carrier transport through tunnel oxide passivated contacts. In particular, structural properties of thin oxide layers are investigated with regard to tunnelling processes and local pinhole conduction. Conductive AFM measurements on n-type TOPCon test structures with and without forced oxide degradation have been performed. The current maps allowed for the first time a spatial-resolved imaging and correlation of the expected oxide degradation and spot like areas with increased currents. The areas are assigned to a different local transport process due to pinhole formation. It was found that a raise of the annealing temperature from 800 °C to 950 °C led to an increase of the pinhole density by 3 due to thermal degradation. The results show a promising approach to study the impact of pinholes to the total conductivity of carrier-selective contact.