Enhancement of NiOx$\left(\text{NiO}\right)_{x}$/Poly-Si Contact Performance by Insertion of an Ultrathin Metallic Ni Interlayer

Nickel oxide (NiOx$\left(\text{NiO}\right)_{x}$) is a promising hole transport material for perovskite/Si tandem solar cells. Various silicon cell architectures may be used as bottom cells. The polycrystalline (poly-Si) p+/n+$\left(\text{p}\right)<^>{+} / \left(\text{n}\right)<^>{+}$ tunnel diode is expected to be a high-efficiency interconnection scheme between the two subcells of monolithic tandems in p-i-n configuration with a high thermal budget, excellent passivation properties, and low contact resistivity. However, NiOx$\left(\text{NiO}\right)_{x}$ is then interfaced to poly-Si(p+$\left(\text{p}\right)<^>{+}$) and the chemical integrity of the interface due to the necessity of annealing treatments has to be questioned. For this purpose, the NiOx$\left(\text{NiO}\right)_{x}$/poly-Si contact resistivity for different annealing temperatures is investigated between 100 and 500 degrees C, and two different NiOx$\left(\text{NiO}\right)_{x}$ deposition techniques, namely, wet-chemically applied and sputter-deposited NiOx$\left(\text{NiO}\right)_{x}$. The values of more than 1 omega cm2$1 \textrm{ } \Omega \textrm{ } \left(\text{cm}\right)<^>{2}$ are obtained. The insertion of a nm-thin metallic Ni interlayer is shown to enable a tremendous decrease of the contact resistivity by 2-3 orders of magnitude. The formation of NiSi2$\left(\text{NiSi}\right)_{2}$ is proven by highly resolved (scanning) transmission electron microscopy ((S)TEM) coupled with energy-dispersive X-ray spectroscopy (EDXS). This interfacial engineering approach is expected to provide an effective way of improving the contact properties and integrability of NiOx$\left(\text{NiO}\right)_{x}$ into various tandem cell processes.