Materials containing unreactive elements are attracting increasing attention for their unexpected characteristics such as pressure-driven superconductivity. However, the known helium-incorporating superconductors (HISCs) are constrained by extreme compression, and thus achieving high-temperature superconductivity in helium-based compounds under moderate pressure is a key challenge. Here, we conducted a comprehensive study of the ${\mathrm{Na}}_2\mathrm{He}$-B system, leveraging a first-principles-assisted configuration prediction method, and presented two previously unknown stable phases, encompassing $P{6}_3/mmc {\mathrm{Na}}_2{\mathrm{HeB}}_2$ and Immm ${\mathrm{Na}}_2{\mathrm{HeB}}_7$. In particular, ${\mathrm{Na}}_2{\mathrm{HeB}}_2$ manifests a prototype hexagonal layered structure featuring interlayer sodium-helium co-insertion and a honeycomb-shaped covalent boron grid. Remarkably, calculations of electron–phonon coupling (EPC) uncover that, among HISCs, ${\mathrm{Na}}_2{\mathrm{HeB}}_2$ holds the highest superconducting transition temperature ($T_c$) at a low pressure of 20 GPa, reaching 38 K, which is primarily attributed to the coupling between in-plane B $2p$ electronic states at the Fermi level and Na- and He-governed low-frequency phonon modes. In contrast, the strategy of enhancing the EPC strength through electronic doping ($-0.04e$/cell) enabled ${\mathrm{Na}}_2{\mathrm{HeB}}_2$ to exhibit high-$T_c$ behavior at 42 K. These findings provide important implications for the discovery of additional superconductors composed of inert elements.

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• Electronic structure
• Phase diagrams
• Structural properties
• Superconductivity
• Crystal structures
• Superconductors
• First-principles calculations