${\mathrm{Bi}}_2{\mathrm{WO}}_6$ is a representative $n$-type photocatalyst; however, a comprehensive understanding is required to enhance its electron carrier concentration $\left(n_{\mathrm{e}}\right)$. Considering intrinsic point defects, we calculate the formation energies, equilibrium Fermi-level positions, and defect/carrier concentrations of ${\mathrm{Bi}}_2{\mathrm{WO}}_6$ by hybrid functional calculations coupled with thermodynamic equilibrium simulations. Through formation energies calculation, we find that the $V_{\mathrm{O}}$ (oxygen vacancy), $V_{\mathrm{Bi}}$ (bismuth vacancy), and ${\mathrm{Bi}}_{\mathrm{W}}$ (bismuth occupies tungsten site) are the dominant intrinsic defects in ${\mathrm{Bi}}_2{\mathrm{WO}}_6$. The dopability results indicate that, unlike the ineffective doping of acceptor $\left(A^{-}\right)$, the donor $\left(D^{+}\right)$ doping can positively enhance the $n_{\mathrm{e}}$ under O-poor conditions; however, this requires a high experimental cost of strict temperature or oxygen partial pressure $\left(p_{\mathrm{O}2}\right)$. Inspiringly, the quench (from 923 to 300 K) strategy can address this issue. Using this strategy, (1) an optimal chemical potential region (OCPR) is obtained in which the $n_{\mathrm{e}}$ is higher, without recombination centers and significant compensation. This suggests that the experimental synthesis conditions should be in OCPR; (2) the $p_{\mathrm{O}2}$ of OCPR ranges from ${10}^{1.67}{p}^0\left(\approx 4.74\times {10}^6\mathrm{Pa}\right)$ to ${10}^{-10.53}{p}^0\left(\approx 3\times {10}^{-6}\mathrm{Pa}\right)$, which includes standard atmospheric pressure (1 atm) conditions. Interestingly, $n_{\mathrm{e}}$ can achieve approximately ${10}^{18}\mathrm{c}{\mathrm{m}}^{-3}$ in OCPR at 300 K and 1 atm, thus significantly reducing the experimental cost; and (3) the doubly positive $V_{\mathrm{O}}$ $\left(V_{\mathrm{O}}^{2+}\right)$ is a desirable donor defect consistent with the experiments, thus leading to $n_{\mathrm{e}}>{10}^{18}\mathrm{c}{\mathrm{m}}^{-3}$ in OCPR under O-poor conditions. Therefore, to obtain high $n_{\mathrm{e}}$ in ${\mathrm{Bi}}_2{\mathrm{WO}}_6$, the following strategies should be applied simultaneously: $D^{+}$ doping, quenching, and decreasing $p_{\mathrm{O}2}$, which is helpful for experimentally designing and synthesizing ${\mathrm{Bi}}_2{\mathrm{WO}}_6$.

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• Defects
• Doping effects
• Point defects
• Doped semiconductors
• Density functional calculations
• Hybrid functionals