Influence of Thermal Activation on Polysilicon Tunnel Junctions for Tunnel Oxide Passivating Contacts‐Based Perovskite/Silicon Tandem Solar Cells

The presented investigation focuses on different thermal activation processes and their influence on the formation of a polysilicon tunnel junction as a recombination layer in perovskite/silicon tandem solar cells. The goals of this investigation are the optimization of the polysilicon tunnel junction and the comparison of different processing pathways to enable a lean process integration. Various process routes with different annealing sequences for the polysilicon tunnel junction were examined, using a laser‐based rapid thermal process (RTP) and a conventional furnace anneal. The main challenge is to control the interdiffusion of p‐ as well as n‐type dopants at the tunnel junction interface during the thermal activation process. On pre‐annealed n‐tunnel oxide passivating contact (TOPCon) layers, a low process temperature for the p‐polysilicon activation is beneficial without the necessity of an additional diffusion blocking layer. If the n‐TOPCon and the p‐polysilicon layer are annealed simultaneously in one RTP, high temperatures are required, which are enabled by a diffusion blocking SiN x interlayer at the tunnel junction interface. Optimized tunnel junctions on TOPCon bottom cell precursors show low contact resistivity of only 30 mΩ cm 2 with an implied open‐circuit voltage as high as 726 mV. These results demonstrate the promising properties of the developed tunnel junctions regarding tandem cell integration.