The π phases are predicted to have 10-20× lower σ with ptype doping, and ∼ 10× lower σ with n-type doping, than their Pnma counterparts (Fig. ). This is partially offset by a 1.5-2× larger |S| (Fig. ), but the net result is that the Pnma phases have up to 8× larger PFs at a reference n = 4 × 10 19 cm -3 . As for the Pnma phases, we predict larger σ but comparable |S| with n-type doping, yielding reasonable PFs of 1.1 and 1.4 mW m -1 K -2 for π SnS and SnSe, respectively, that can be enhanced to 1.7 and 2.3 mW m -1 K -2 at a larger n = 10 20 cm -3 (Fig. ). On the other hand, at higher n the κ el are proportional to the σ through the Wiedemann-Franz law,