Chemico-physical interactions in metal halide perovskites

Metal halide perovskite (MHP) has attracted tremendous attention due to its success in optoelectronics, largely due to outstanding photovoltaic performance. A wide variety of characterization approaches have been used to explore the fundamentals behind the outstanding optoelectronic properties of MHP, which has yet to be unambiguously established despite considerable efforts to do so. Given the high ionic mobility in MHP, when physical phenomena are coupled with chemical changes, all behaviors will become very complex due to the strong ion migration. Therefore, chemico-physical interactions in MHP can no longer be ignored, which will be the focus of the researches in this thesis. First, the nature of the ferroic twin domain in CH₃NH₃PbI₃, a prototypical MHP, is revealed in Chapter 2. The study indicates the chemical and elastic inhomogeneity is the main origin of the twin domain contrast in piezoelectric force microscopy measurements, which has been widely attributed to ferroelectricity previously. Following on, the effects of the twin domain on the optoelectronic properties of CH₃NH₃PbI₃ are investigated in Chapter 3, revealing the effect of domains on light-matter interaction and the potential effect of domain walls on charge transport. Chapter 4 reports a series of studies about ion migration in MHP, including light-induced migration, electric-induced migration, migration of intrinsic ions and decomposition ions, and ion migration related charge dynamics and device operation. Chapter 5 presents studies regarding the interactions of ferroic, chemical, structural, and electronic properties of MHP. Finally, Chapter 6 summarizes the research results in this thesis and offers an outlook for future researches.