Carrier Decay Properties of Mixed Cation Formamidinium–Methylammonium Lead Iodide Perovskite [HC(NH<sub>2</sub>)<sub>2</sub>]<sub>1–<i>x</i></sub>[CH<sub>3</sub>NH<sub>3</sub>]<sub><i>x</i></sub>PbI<sub>3</sub> Nanorods

Organic–inorganic lead iodide perovskites are efficient materials for photovoltaics and light-emitting diodes. We report carrier decay dynamics of nanorods of mixed cation formamidinium and methylammonium lead iodide perovskites [HC­(NH<sub>2</sub>)<sub>2</sub>]<sub>1–<i>x</i></sub>[CH<sub>3</sub>NH<sub>3</sub>]<sub><i>x</i></sub>PbI<sub>3</sub> (FA<sub>1–<i>x</i></sub>MA<sub><i>x</i></sub>PbI<sub>3</sub>) synthesized through a simple solution method. The structure and FA/MA composition ratio of the single-crystal FA<sub>1–<i>x</i></sub>MA<sub><i>x</i></sub>PbI<sub>3</sub> nanorods are fully characterized, which shows that the mixed cation FA<sub>1–<i>x</i></sub>MA<sub><i>x</i></sub>PbI<sub>3</sub> nanorods are stabilized in the perovskite structure. The photoluminescence (PL) emission from FA<sub>1–<i>x</i></sub>MA<sub><i>x</i></sub>PbI<sub>3</sub> nanorods continuously shifts from 821 to 782 nm as the MA ratio (<i>x</i>) increases from 0 to 1 and is shown to be inhomogeneously broadened. Time-resolved PL from individual FA<sub>1–<i>x</i></sub>MA<sub><i>x</i></sub>PbI<sub>3</sub> nanorods demonstrates that lifetimes of mixed cation FA<sub>1–<i>x</i></sub>MA<sub><i>x</i></sub>PbI<sub>3</sub> nanorods are longer than those of the pure FAPbI<sub>3</sub> or MAPbI<sub>3</sub> nanorods, and the FA<sub>0.4</sub>MA<sub>0.6</sub>PbI<sub>3</sub> displays the longest average PL lifetime of about 2 μs. These results suggest that mixed cation FA<sub>1–<i>x</i></sub>MA<sub><i>x</i></sub>PbI<sub>3</sub> perovskites are promising for high-efficiency photovoltaics and other optoelectronic applications.