| Description |
In the last decade, the organic/inorganic hybrid perovskites have emerged as one of the most promising classes of contenders for low-cost solar cells, owing to extraordinary power conversion efficiencies of more than 22%, and convenient solution fabrication processes. Moreover, the hybrid perovskite systems have found applications in many other fields, such as light emitting diodes, lasers, field effect transistors, and spintronics. In this dissertation, by using a variety of transient and steady-state optical measurements, we have investigated the photoexcitations in different organic/inorganic hybrid perovskite systems, including three- (3D) and two- (2D) dimensional thin films and single crystals. In 3D hybrid perovskites, we have identified the excitons/photocarriers duality nature in the lead iodine perovskite at room temperature (RT), which is consistent with its small exciton binding energy (Eb) less than kBT for T=300K. For lead bromide and lead cloride perovskites with larger Eb , excitons have been verified as the the primary photoexcitations. These results show that the branching ratio between the photogenerated excitons and free carriers is determined by the exciton binding energy in the hybrid perovskites. Due to the anistropic teragonal structure phase, we have also observed the polarization memory (POM) dynamics of both excitons and free carriers in the lead iodine perovskite, from which we have estimated the long exciton diffusion length at 150nm. In addition, the effects of nano-morphologies on photoluminescence and magnetic properites in perovskites have also been studied. In 2D hybrid perovskites, we have found a strong photoinduced absorption (PA) from the primary exciton state to the upper branch of the Rashba-splitting band, from which we have obtained a giant Rashba-splitting in this compound, with the Rashba-splitting energy, ER= 40/pm 5 meV and Rashba-splitting parameter αR=1.6/pm 0.1 eV·Å that is among the highest values reported so far. We have extended our measurements to lead bromide perovskite single crystals, which show much lower trap state densities and longer exciton lifetimes in the bulk than in the film samples. Our observation of a fast photobleaching (PB) and a corresponding rise of PA in the near-surface regime reveals the process of the exciton recombination on the surface and diffusion to the interior of the bulk. |
