Hybrid halide perovskites are a promising class of materials due to the high efficiency of solar cells based on the parent compound, CH₃NH₃PbI_3. An interesting aspect of these materials is that their properties can be modified by changing the composition, for instance exchanging the halide, the organic cation or the Pb²⁺. In this work we study how the composition of the material influences the mobility and decay kinetics of charge carriers at different temperatures. To study this, we have used the unique pulse radiolysis time-resolved microwave conductivity technique, where charges are generated by irradiation with high-energy electron pulse and probed by microwave absorption.

 For CH₃NH₃PbI₃ the mobility of charge carriers was found to depend significantly on temperature, showing a slow increase up to the phase transition from the tetragonal (β) to the orthorhombic (γ) phase. Upon the phase transition a sharp rise in mobility is observed, indicating the marked effect of the crystal structure on the mobility. In addition to the change in mobility, we also observe a drastic increase of the life-time of charges on transition to the low-temperature phase. Both of these observations are rationalized in terms of the reduced rotational freedom of the organic cation at low temperature. A detailed study of the dependence of the decay of the conductivity in time shows that the decay is consistent with second order recombination kinetics with the presence of a limited concentration of trap states.  

In addition, we have studied different perovskites, exchanging the halide atom (X₃=I₂Br, IBr₂, Br₃ and Cl₃) and the organic cation (A= NH₂CHNH₂). The dependence of the charge carrier mobility on the nature of the halide ion was found to be relatively weak. All compounds show charge mobilities of ≈2 cm²/Vs at room temperature. Decreasing the temperature increases the mobilities exhibiting similar sudden changes after the β/γ phase transition. For CH₃NH₃PbCl₃ the mobility is more than an order of magnitude lower. The latter is attributed diffusion of the halide ions in the lattice. 

The exchange of the CH₃NH₃ by NH₂CHNH₂ produced different isomers at room temperature with mobilities that differ by one order of magnitude. This difference is traced back to the much higher effective masses in the yellow-layered phase. Additionally, the black perovskite phase exhibits exceptionally long charge life times up to tens of microseconds and less sudden increments after the β/γ phase transition.