Thermal Stability of Mixed Cation Metal Halide Perovskites in Air.

We study the thermal stability in air of the mixed cation organic-inorganic lead halide perovskites CsFAPb(IBr) and Cs(MAFA)Pb(IBr). 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 °C). For the second stage, we find that both decomposition rate and the activation energy have similar values for Cs(MAFA)Pb(IBr) and CsFAPb(IBr), which suggests that the first stage mainly involves reaction of MA and the second stage mainly FA.