Fundamental Insights into Halide Ion Migration and Exchange in Persovkites Nanocrystals

Halide perovskite nanocrystals have been identified as a prospective candidate for future optoelectronic devices. such as solar cells, LEDs, scintillators, and photo/radiation detectors. Their excellent optoelectronic properties such as large absorption coefficient, high carrier mobility, wide color gamut, long electron-hole diffusion lengths, and tunable bandgap energy are largely responsible for their wide acceptability in various electronic devices. However, despite the recent developments, the problem of instability remains a major obstacle toward their commercialization. For example, ion migration has been reported to cause phase separation in mixed halide perovskite-based optoelectronics which ultimately leads to instability and a decrease in photovoltaic performance. Therefore, many researchers have devoted attention to understanding the process of this ion migration in various mixed halide perovskites CsPb(I_1-xBr_x)₃of different compositions. However, to date, the processes underlying this anion migration and exchange remain under debate and largely unclear. Here, we elucidated the processes involved during halide ion exchange and migration in lead perovskite nanocrystals. In addition to this, we also quantify the thermodynamics of this ion exchange, therefore, revealing the origin of phase separation commonly encountered in mixed CsPb(I_1-xBr_x)₃ halide perovskites-based optoelectronics. Our fundamental understanding of the process of this anion exchange and migration will help provide better-informed guidelines toward engineering perovskite nanocrystals for different applications such as tandem cells and efficient devices for lighting and display technology.