Tuning Nonradiative Recombination via Cation Substitution in Inorganic Antiperovskite Nitrides

Inorganic antiperovskite nitrides have recently emerged as promising materials for photovoltaic applications, yet their nonradiative recombination dynamics remain largely unexplored. Here, we examine the influence of X-site cation substitution on the nonradiative electron-hole recombination in $\mathrm{X_{3}NSb}$ ($X = \mathrm{Ca}, \mathrm{Sr}, \mathrm{Ba}$). Ca- and Sr-based compounds adopt a cubic phase, whereas Ba stabilizes in a hexagonal structure, introducing pronounced symmetry-driven effects. Substituting Ca with Sr narrows the band gap, suppresses octahedral and band-edge fluctuations, reduces nonadiabatic (NA) coupling by $\sim 54\%$, and extends carrier lifetimes by a factor of $2.5$. In contrast, Ba substitution increases lattice distortion, widens the band gap, and enhances NA coupling beyond that of $\mathrm{Sr_{3}NSb}$, thereby accelerating recombination through stronger lattice fluctuations. The resulting band gap fluctuations in $\mathrm{Ba_{3}NSb}$ also shorten decoherence times, following the trend $\mathrm{Ba_{3}NSb} < \mathrm{Ca_{3}NSb} < \mathrm{Sr_{3}NSb}$. Our results demonstrate how the interplay between band gap, NA coupling, and decoherence time governs recombination lifetimes, with $\mathrm{Sr_{3}NSb}$ exhibiting the longest lifetime. These findings highlight the coupled influence of cation chemistry and crystal symmetry in tailoring carrier dynamics for high-performance antiperovskite-based optoelectronics materials.