Direct and Indirect Recombination and Thermal Kinetics of Excitons in Colloidal All-Inorganic Lead Halide Perovskite Nanocrystals

In recent years, the colloidal all-inorganic lead halide perovskite nanocrystal has become one of the most notable optoelectronic materials. The kinetics of excitons directly influence the device performance, but it is very complicated and still unclear. Here, we have presented the investigation of thermal kinetics of excitons in colloidal all-inorganic lead halide perovskite nanocrystals. As temperature increases from 4 K to room temperature, the photoluminescence (PL) intensity follows the Arrhenius equation with interruption at 130-150 K, while the average PL lifetime follows the double-Boltzmann function fitting, discontinuing at the same temperature. These experimental results could be explained by direct and indirect recombination of excitons. The excitons directly recombine with a short lifetime of about 300 ps. Indirect recombination is completed by the photo excited electrons (holes) along the path of trapping,, detrapping, and then recombination with holes (electrons). The excitons mainly undergo indirect recombination at low temperature and balance at the temperature of 130-150 K because of thermal activation, while direct recombination happens at high temperature. Our experimental results provide insight into the recombination mechanism of excitons in colloidal all-inorganic lead halide perovskite nanocrystals, which will be helpful to unravel their potential for high-performance optoelectronic devices.