Passivating Silicon Tunnel Diode for Perovskite on Silicon Nip Tandem Solar Cells

Abstract

Silicon solar cells featuring tunnel oxide passivated contacts (TOPCon) benefit from high efficiencies and low production costs and are on the verge of emerging as the new photovoltaic market mainstream technology. Their association with Perovskite cells in 2-terminal tandem devices enables efficiency breakthroughs while maintaining low fabrication costs. However, it requires the design of a highly specific interface to ensure both optical and electrical continuities between subcells. Here, we evaluated the potential of tunnel diodes as an alternative to ITO thin films, the reference for such applications. The PECV deposition of an nc-Si (n+) layer on top of a boron-doped poly-Si/SiOx passivated contact forms a diode with high doping levels (>2 × 1020 carrier·cm−3) and a sharp junction (<4 nm), thus reaching both ESAKI-like tunnel diode requirements. SIMS measurements of the nc-Si (n+) (deposited at 230 °C) reveal an H-rich layer. Interestingly, subsequent annealing at 400 °C led to a passivation improvement associated with the hydrogenation of the buried poly-Si/SiOx stack. Dark I–V measurements reveal similar characteristics for resistivity samples with or without the nc-Si (n+) layer, and modeling results confirm that highly conductive junctions are obtained. Finally, we produced 9 cm2 nip perovskite on silicon tandem devices, integrating a tunnel diode as the recombination junction between both subcells. Working devices with 18.8% average efficiency were obtained, with only 1.1%abs PCE losses compared with those of references. Thus, tunnel diodes appear to be an efficient, industrially suitable, and indium-free alternative to ITO thin films.