Unveiling the large polarons in antiperovskite X₃NA (X²⁺ = Mg²⁺, Ca²⁺, Sr²⁺; A³⁻ = P³⁻, As³⁻, Sb³⁻, Bi³⁻)

Antiperovskites have emerged as promising candidates for optoelectronic devices due to their remarkable structural tunability and diverse physicochemical properties. Carrier transport characteristics are critical to the performance of these devices, yet the specific transport mechanisms in antiperovskite X₃NA (X²⁺ = Mg²⁺, Ca²⁺, Sr²⁺; A³⁻ = P³⁻, As³⁻, Sb³⁻, Bi³⁻) remain poorly understood. In this study, we investigate the carrier transport properties of antiperovskite X₃NA using first-principles calculations and the Boltzmann transport equation. Our results reveal that the carrier mobility of X₃NA is primarily limited by Fröhlich-type polar optical phonon scattering. The moderate Fröhlich coupling constants (0.26 ≤ α ≤ 1.66) suggest weak electron-phonon coupling in X₃NA, resulting in high mobility up to 461.4 cm²/Vs, surpassing that of prototypical halide perovskites (∼ 80.0 cm²/Vs). These findings indicate that the carrier transport in X₃NA is governed by large polarons. Finally, we show that the strain can modulate the effective mass and electron-phonon coupling strength, thereby enabling tunable carrier mobility in Mg₃NSb. This work highlights the exceptional intrinsic carrier transport properties and strain tunability of X₃NA, making them promising candidates for the future development of high-performance optoelectronic devices.