Controlling Diffusion in Poly-Si Tunneling Junctions for Monolithic Perovskite/Silicon Tandem Solar Cells

The performance of a low-resistive p ⁺ /n ⁺ poly-Si tunneling junction (SiTJ) based on a tunnel oxide passivating contact in dependence on the thermal budget of the applied post-deposition treatment is studied. We present two approaches to reduce the performance limiting parasitic dopant interdiffusion and, thus, the contact resistivity, without impairing the passivation quality. Both, carbon-alloying of poly-Si layers and the application of diffusion blocking interlayers are effective means to maintain a low contact resistivity of ∼24 mΩcm ² at high thermal process temperatures of up to 950 °C. Those low values are obtained using either a standard furnace anneal or a rapid thermal process (RTP). We report on promising results toward a lean process sequence using only one single fast thermal treatment (RTP-only). As a main result, the flexibility for engineering and fabrication of our SiTJ was markedly improved, eventually facilitating industrially feasible perovskite/silicon tandem solar cells. One aspect being higher post-deposition temperatures needed for, e.g., bottom cell rear side contact formation and the first layers of the perovskite to cell.