Spin Dynamics in Halide Perovskite and Organic Long Persistent Light Emission Materials

The functional materials are of critical importance to the development of semiconductor devices, medical imaging, energy storage, etc. In this dissertation, two functional materials, halide perovskites (HPVs) and organic long persistent luminescence (OLPL) material, are studied. Chapter 1 of this dissertation presents an introduction to HPV and OLPL materials.

The first functional material, halide perovskite (HPV), has been heralded as one of the most promising emerging technologies owing to its remarkable photovoltaic performance and low-cost solution processability. The three-dimensional (3D) HPV solar cells have achieved an efficiency comparable to the commercialized solar cells. The bulk polarization and spin states are critical for promoting solar cell efficiency, however, the significant photo-induced bulk polarization process in 3D HPVs is still controversial and the interaction between polarization and spin-orbit coupling is still unclear. Chapter 2 identifies the photoinduced bulk polarization and the interaction between dipolar polarization and spin-orbit coupling in 3D HPVs. Furthermore, the highly tunable crystal structure of HPVs enables their various dimensionalities from 3D structure to 0D structure, and the 0D HPV typically exhibits larger bandgaps due to the spatial confinement effect. Nevertheless, recent reports insufficiently decipher the origin of the abnormal far below bandgap low-energy emission and explore their non-linear optical properties. In Chapter 3, we revealed the origin of the far below bandgap green emission in 0D HPV, also showed its polarized emission in both down-conversion and up-conversion emission regimes.

The other functional material, OLPL material, has achieved remarkable breakthroughs in recent years that enable long-lived light emission in metal-free purely organic materials at room temperature. However, the experimental evidence to identify spin characteristics of the critical long lifetime excited states in room temperature OLPL is still lacking. In addition, the non-linear optical properties in OLPL materials have not been well studied. Here, Chapter 4 deciphers the spin characteristics of the special intermolecular light-emitting states, also exhibits a slow phonon effect which is critical to the generation of OLPL. Chapter 5 exhibits the multiphoton up-conversion afterglow phenomenon and identifies the long-lived excited states within the ferroelectric lattice in OLPL material.