${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}$ is an emerging high-performance layered semiconductor with excellent stability. While experimental studies have explored carrier transport across various doping levels for both $n$-type and $p$-type conduction, a comprehensive theoretical understanding remains incomplete. In this work, we present parameter-free first-principles calculations of the electron and hole mobilities in ${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}$, based on iterative solution of the Boltzmann transport equation that includes electron-phonon scattering and ionized impurity scattering on an equal footing. Intriguingly, we find that ${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}$ exhibits high electron mobilities in both the in-plane and out-of-plane directions, whereas the hole mobilities are only significant in the in-plane direction, displaying a unique three-dimensional electron transport and two-dimensional hole transport behavior. At 300 K, the calculated intrinsic electron and hole mobilities along the in-plane direction are 447 ${\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ and 29 ${\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$, respectively, which are primarily affected by Fröhlich electron-phonon interactions. Due to its large static dielectric permittivity, ${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}$ exhibits exceptionally high low-temperature electron mobilities above $1.0\times {10}^5{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$, and its electron mobilities above 50 K are robust against ionized impurity scattering over a wide range of impurity concentrations. By incorporating the Hall effect into our analysis, we predict an in-plane electron Hall mobility of 517 ${\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ at 300 K, in excellent agreement with experimental data. These results provide valuable insights into the carrier transport mechanisms in ${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}$, and offer predictive benchmarks for future theoretical and experimental investigations.

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• Carrier dynamics
• Electron-phonon coupling
• Semiconductors
• Boltzmann theory
• Density functional calculations
• Perturbation theory