Thermally activated exciton dissociation and recombination control the carrier dynamics in organometal halide perovskite

Solar cells based on organometal halide perovskites have seen rapidly increasing efficiencies, now exceeding 15%. Despite this progress, there is still limited knowledge on the fundamental photophysics. Here we use microwave photoconductance and photoluminescence measurements to investigate the temperature dependence of the carrier generation, mobility, and recombination in (CH₃NH₃)PbI₃. At temperatures maintaining the tetragonal crystal phase of the perovskite, we find an exciton binding energy of about 32 meV, leading to a temperature-dependent yield of highly mobile (6.2 cm²/(V s) at 300 K) charge carriers. At higher laser intensities, second-order recombination with a rate constant of γ = 13 × 10 ^-10 cm³ s^-1 becomes apparent. Reducing the temperature results in increasing charge carrier mobilities following a T ^-1.6 dependence, which we attribute to a reduction in phonon scattering (σμ = 16 cm²/(V s) at 165 K). Despite the fact that σμ increases, γ diminishes with a factor six, implying that charge recombination in (CH₃NH₃)PbI₃ is temperature activated. The results underline the importance of the perovskite crystal structure, the exciton binding energy, and the activation energy for recombination as key factors in optimizing new perovskite materials.