There have been a limited number of experimental studies on the π phases for photovoltaic applications. Measurements on thin films of n-type π SnS yielded a conductivity of 0.1 S cm -1 at 673 K and n = 3.7 × 10 17 cm -3 , which is comparable to our predicted 0.7 S cm -1 . Similarly, measurements on Sn(S 0.45 Se 0.55 ) films obtained a p-type conductivity of 2 × 10 -2 S cm -1 at 723 K and n = 10 16 cm -3 , 77 which falls between our predicted σ = 0.9 × 10 -2 and 6 × 10 -2 S cm -1 for π SnS and SnSe. Nair et al. reported that the room-temperature σ of Pnma SnS and SnSe are 2-3 orders of magnitude larger than the corresponding π phases, which is qualitatively consistent with our findings. The Seebeck coefficients of 485 and 314 µV K -1 measured for p-type SnS-SnSe and SnS-SnSe-SnS stacks with n = 9 × 10 15 and 10 15 cm -3 are less than half the maximum we predict. Our calculations on both π structures suggest the S change sign with temperature at low n, which would account for this discrepancy (Figs S13/S14 † ).