Design and controlled vdW epitaxy of WSe2/PbI2 heterostructure for robust momentum-direct interlayer exciton emission at room temperature

Interlayer excitons (IXs) in van der Waals (vdW) heterostructures offer prolonged lifetimes and electrically tunable dipoles, enabling advanced excitonic devices and coherent light sources. However, achieving stable and efficient room temperature IX emission for applications requires vdW systems with both momentum-matched band alignment and feasible scalable fabrication capability, which is still challenging. Here, we propose to address this issue by demonstrating vdW epitaxy of a uniformly distributed bilayered 2H-WSe2/PbI2 heterojunction, which exhibits uniform and stable IX emission at 1.36 eV at room temperature. First-principle calculations and experiments confirm that the momentum-direct IX emission at the Γ point is possible. Thanks to the inorganic nature of PbI2, the occurrence of IX emission is air stable. The IX emission intensity retains 84.2% of its initial intensity after 4 months in ambient condition. The high IX binding energy (85.3 meV), long lifetime (3.77 ns), and large blueshift (45 meV) during power-dependent emission spectra demonstrate the strong Coulomb interactions and robust nature of the IXs. More delightfully, the valley information in IXs is preserved, showing a stable valley polarization degree of 19.58% at 83 K. These results indicate that the bilayered 2H-WSe2/PbI2 heterojunction is a promising platform for promoting the development of IX-related fundamental science research and applications.