Polarized emission effect realized in CH₃NH₃PbI₃ perovskite nanocrystals

In this study, we present a detailed investigation of the optical properties of organic-inorganic hybrid perovskite CH₃NH₃PbI₃ nanocrystals (NCs). Temperature-dependent steady-state and time-resolved photoluminescence (PL) measurements were employed to understand the optical transition mechanisms and carrier recombination dynamics of CH₃NH₃PbI₃ NCs. X-ray diffraction results showed a structural phase transition from the tetragonal to orthorhombic phase states during a cooling process although the PL results at low temperature revealed no signs of orthorhombic phase related emission. We analyzed in detail the possible reasons from three perspectives. In addition to the exciton related emission, two trap-mediated exciton emissions appear at low temperatures of 180 and 100 K because of the smaller binding energies of trapped excitons than that of free excitons. The corresponding exciton binding energy, optical phonon energy, and temperature sensitivity coefficient of the bandgap for CH₃NH₃PbI₃ NCs were extracted from the experimental data. More importantly, we demonstrated the linearly polarized emission from the as-synthesized CH₃NH₃PbI₃ NCs, and a linear polarization degree of 0.28 was obtained. It is reasonably believed that our obtained results open up possibilities for the development of new generation displays by using novel perovskite NCs with a high polarization property.