“…The PF of the CZFCTS-1 thin films was substantially improved by annealing (Figure c). Compared to the CZTS films (Figure ), the CZFCTS-1 thin films annealed for 24 h show significant enhancement in maximum PF, by a factor of ∼22, with a PF of ∼2.4 μW cm –1 K –2 at 575 K. Figure e provides a comparison of the maximum PF values obtained in this work to that of published data for analogous polycrystalline quaternary sulfide (Cu 2 BSnS 4 (CBTS), where B = Mn, Fe, Co, Ni) bulk materials and thin films. ,,,,,,− Our maximum PF values are significantly higher than all previous reports for single-phase CZTS-based thin films and most polycrystalline bulk materials. This outstanding result demonstrates that cosubstitution of high levels of Cd and Fe into CZTS is an effective approach to increasing the power factor of thin films, and, furthermore, that postdeposition annealing can both enhance film quality and significantly improve charge transport.…”