New Approach for a Combined Process of an Ultrafast Boron-Oxygen Defect Regeneration and Thermal Contact Treatment of Ni/Cu/Ag Plated Solar Cells

A plating sequence of the passivated emitter and rear cell (PERC) concept with Ni/Cu/Ag plated contacts which includes boron-oxygen (BO) defect regeneration and contact annealing is required to ensure a high and light stable efficiency accompanied by a low contact resistance. We introduce an inline-capable process of boronoxygen (BO) defect regeneration with a simultaneous annealing of the Ni/Cu/Ag plated contact within 10 seconds or less. As basis for the development of the inline capable process a transfer line method (TLM) test structure was used to identify process parameters with respect to time scale, temperature and illumination density. The experimental results demonstrate that an optimized process for simultaneous contact annealing and BO regeneration can achieve a full contact anneal after 1 second and an almost complete BO regeneration after 10 seconds. At higher temperatures above 500 °C a possible shunting through the emitter occurs along with no BO regeneration. Whereas lower temperature of 100 °C slows down contact annealing and BO regeneration significantly to a non-inline practicable process time. Hence, a good process window for complete BO regeneration and contact annealing was observed at a temperature of 250 °C with an illumination density of 27 kW/m². Subsequently, the combined process was successfully transferred to an inline capable tool, which enables a significant speed-up of the contact annealing with simultaneous high BO regeneration. Furthermore, a smaller footprint, no need of nitrogen-rich atmosphere and reduced energy consumption are possible advantages compared to an inline thermal treatment oven for contact annealing.