High-temperature superconductivity in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$-derived films with critical temperatures ($T_{\mathrm{c}}$) of 40–50 K has so far been realized only under substrate-induced compressive strain. Here we use first-principles calculations to predict that such ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ films can be stably grown on designer substrates ${\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_x\mathrm{O}$ ($x=1–0$) and SrO-terminated ${\mathrm{SrTiO}}_3$ ($\mathrm{SrO}\text{−}{\mathrm{SrTiO}}_3$) with improved film quality and continuously tunable epitaxial strain, offering physically realistic materials platforms to achieve enhanced superconductivity. In particular, under the optimal tensile strain of $\sim 2\%$ imposed by ${\mathrm{Ba}}_{0.75}{\mathrm{S}}_{0.25}\mathrm{O}$ or $\mathrm{SrO}\text{−}{\mathrm{SrTiO}}_3$, the ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ films are energetically stable within a desirable thickness range, and more resilient against oxygen vacancy formation. Concomitantly, the lattice constant normal to the films is effectively reduced, and the Ni $d_{z^2}$ orbital is peaked near the Fermi level and hybridizes with the Ni $d_{x^2-y^2}$ orbital, features that closely resemble their bulk counterparts at high pressure and strongly point to superconductivity with higher $T_{\mathrm{c}}$. These findings establish innovative routes toward realizing enhanced superconductivity in tensile-strained ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ films, and allow to critically assess the role of the Ni $d_{z^2}$ orbital in superconducting pairing.

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• Electronic structure
• Superconductivity
• Interfaces
• Unconventional superconductors