The fundamental physical properties of Cs2PtI6 and (CH3NH3)2PtI6

The study of physical properties of Cs2PtI6 and MA2PtI6 (MA+ = CH3NH3+) is performed and discussed for the first time. The stability of trigonal structure MA2PtI6 is verified by the formation energy. Moreover, the weakened stability is revealed from Cs2PtI6 to MA2PtI6. The results show that the introduction of MA + cation in Cs2PtI6 will result in structural phase transition. The band gap nature is varied from Cs2PtI6 to MA2PtI6. Cs2PtI6 is a direct semiconductor material at the Γ point with the band gap of 1.08 eV. The calculated values are 1.47 and 1.64 eV for the indirect and direct band gaps of MA2PtI6. The absorption coefficient of MA2PtI6 is slightly lower than that of Cs2PtI6. Our findings are highly consistent with the experimental results.