Enhancement of NiO${}_x$/poly-Si contact performance by insertion of an ultrathin metallic Ni interlayer

Nickel oxide (NiO${}_x$) 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${}^{+}$ 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, NiO${}_x$ is then interfaced to poly-Si(p${}^{+}$) and the chemical integrity of the interface due to the necessity of annealing treatments has to be questioned. For this purpose, the NiO${}_x$/poly-Si contact resistivity for different annealing temperatures is investigated between 100 and 500 °C, and two different NiO${}_x$ deposition techniques, namely, wet-chemically applied and sputter-deposited NiO${}_x$. The values of more than 1 $\Omega$ cm${}^2$ 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 NiSi${}_2$ 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 NiO${}_x$ into various tandem cell processes. (© 2023 The Authors. physica status solidi (a) applications and materials science published by Wiley‐VCH GmbH)