Thermal Stability of Mixed Cation Metal Halide Perovskites in Air

We study the thermal stability in air of the mixed cation organicinorganic lead halide perovskites Cs(0.17)FA(0.83)Pb(I0.83Br0.17)(3) and Cs-0.05(MA(0.17)FA(0.83))(0.95)Pb(I0.83Br0.17)(3). For the latter compound, containing both MA+ and FA+ ions, thermal decomposition of the perovskite phase was observed to occur in two stages. The first stage of decomposition occurs at a faster rate compared to the second stage and is only observed at relatively low temperatures (T < 150 degrees C). For the second stage, we find that both decomposition rate and the activation energy have similar values for Cs-0.05(MA(0.17)FA(0.83))(0.95)Pb(I0.83Br0.17)(3) and Cs(0.17)FA(0.83)Pb(I0.83Br0.17)(3), which suggests that the first stage mainly involves reaction of MA+ and the second stage mainly FA(+).