Harnessing Linear and Nonlinear Optical Responses in Ferroelectric LaMoN ₃ for Enhanced Photovoltaic Efficiency

Nitride perovskites are an emerging class of materials predicted to exhibit diverse functional properties, yet remain underexplored due to synthesis challenges of oxygen-free nitrides. Recently, LaMoN 3 has been reported as an oxygen-free nitride perovskite with polar symmetry, exhibiting excellent dynamic stability and ferroelectric properties under moderate pressure. However, its phase stability, linear and nonlinear optical response, excitonic and polaronic behavior, and efficiency under high pressure remain unexplored. Applying pressure enables systematic tuning of the electronic structure properties, thereby facilitating the identification of phases optimized for either linear or nonlinear optical responses. Therefore, in this work, we systematically investigate these properties of LaMoN 3 up to 40 GPa using first-principles methods, including density functional theory, density functional perturbation theory, many-body perturbation theory (namely G 0 W 0 and BSE), and tight-binding model. Our study shows that LaMoN 3 remains dynamically stable and retains its single-phase structure up to 40 GPa. The compound exhibits an indirect bandgap that decreases from 2.17 eV (0 GPa) to 1.45 eV (40 GPa) at the G 0 W 0 @PBE level. Using the BSE, we find that pressure enhances the SLME while lowering the exciton binding energy, both favorable for photovoltaic applications. Additionally, carrier-phonon interactions, analyzed via the Fröhlich model, are found to strengthen under pressure, resulting in reduced carrier mobility. Complementing these findings, bulk photovoltaic (BPV) and nonlinear effects were studied. The BPV efficiency trend with pressure mimics the behavior of the shift current density J SC, peaking near 15 GPa before declining at higher pressures due to a diminished nonlinear shift current response. These results highlight pressure-tuned regimes to enhance photovoltaic performance. We thereby propose multijunction device, that combines the absorber layers optimized for linear and nonlinear optical currents: the 40 GPa phase enables efficient linear response in micrometer-scale absorbers, while the 15 GPa phase maximizes nonlinear current in nanometer-scale absorbers, together boosting solar energy conversion through complementary mechanisms.