Elemental superconductors serve as essential model systems because their compositional simplicity enables fundamental mechanisms to be probed with minimal extrinsic complexity. Their superconducting transition temperatures ($T_{\mathrm{c}}$), however, are generally low, with the notable exception of scandium, which reaches 36 K at 260 GPa—the highest $T_{\mathrm{c}}$ reported for any elemental material. Although bulk boron is semiconducting at ambient pressure, two-dimensional boron monolayers (borophenes) exhibit rich structural polymorphism, and several phases are predicted to be superconducting with $T_{\mathrm{c}}$ values of 3.7–27.6 K, limited by relatively weak electron-phonon coupling. Here, we show that borophene bilayers, stabilized by interlayer B-B bonds, unexpectedly enhance the electronic density of states near the Fermi level and promote cooperative electron-phonon interactions, in which $p_{\text{x},\text{y}}$ states couple to in-plane phonons and $p_{\text{z}}$ states to out-of-plane modes. A high-throughput search of more than 9000 bilayer configurations identifies an $AA$-stacked, low-energy $v_{1/7}$ structure with $T_{\mathrm{c}}\approx 68\mathrm{K}$, setting a new record for elemental superconductivity.

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• Electron-phonon coupling
• Superconducting gap
• Superconductivity