The steep increase in σ at larger n, together with the shallow variation in S, means that the PFs of Bi 2 SO 2 and Bi 2 SeO 2 are dominated by the electrical conductivity and reach a plateau around the largest n = 10 21 examined in the calculations. For Bi 2 TeO 2 , on the other hand, the slower decrease in |S| at large n means the PF shows a broad peak at a lower n ≈ 10 20 cm -3 . We predict Bi 2 SeO 2 and Bi 2 TeO 2 can achieve comparable PFs, with a lower n required for the telluride, whereas we predict Bi 2 SO 2 to attain a maximum n-type PF around ∼ 60% of the heavier oxychalcogenides.