Charge Carriers in Planar and Meso-Structured Organic-Inorganic Perovskites: Mobilities, Lifetimes, and Concentrations of Trap States

Efficient solar cells have been obtained using thin films of solution-processed organic-inorganic perovskites. However, there remains limited knowledge about the relationship between preparation route and optoelectronic properties. We use complementary time-resolved microwave conductivity (TRMC) and photoluminescence (PL) measurements to investigate the charge carrier dynamics in thin planar films of CH₃NH₃PbI_3-xCl_x, CH₃NH₃PbI₃, and their meso-structured analogues. High mobilities close to 30 cm²/(V s) and microsecond-long lifetimes are found in thin films of CH₃NH₃PbI_3-xCl_x, compared to lifetimes of only a few hundred nanoseconds in CH₃NH₃PbI₃ and meso-structured perovskites. We describe our TRMC and PL experiments with a global kinetic model, using one set of kinetic parameters characteristic for each sample. We find that the trap density is less than 5 × 10¹⁴ cm^-3 in CH₃NH₃PbI_3-xCl_x, 6 × 10¹⁶ cm^-3 in the CH₃NH₃PbI₃ thin film and ca. 10¹⁵ cm^-3 in both meso-structured perovskites. Furthermore, our results imply that band-to-band recombination is enhanced by the presence of dark carriers resulting from unintentional doping of the perovskites. Finally, our general approach to determine concentrations of trap states and dark carriers is also highly relevant to other semiconductor materials.