Enhancement of NiO_x/Poly‐Si Contact Performance by Insertion of an Ultrathin Metallic Ni Interlayer

Abstract

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+false/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 °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 Ω 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.

Titanium Silicide: A Promising Candidate of Recombination Layer for Perovskite/Tunnel Oxide Passivated Contact Silicon Two-Terminal Tandem Solar Cells

“…As the oxidation time increased, Ti within the SiO X gradually diffused toward the Si ( Figure 2 d) and reacted with the Si atoms to form TiSi 2 ( Figure 2 e). Recently, Lange et al 39 reported a similar atomic distribution by annealing Ni to form nickel silicide above the poly-Si layer, stating that the metallic Ni atoms inside the SiO X layer serve as a pathway for current flow.…”

“… 38 NiSi, formed between NiO X and n + poly-Si, assists carrier transportation, resulting in ohmic current–voltage ( I – V ) characteristics. Lange et al 39 also used a NiSi interlayer to improve the NiO X /poly-Si contact properties. However, the performances of tandem devices with silicide-based interlayers have not yet been reported.…”