2 Characterization of the crystallization kinetics
As we discussed above, intensively structure evolution occurs during film-forming process and post-treatment process, which determines the final morphology of the active layer. Therefore, monitoring structure evolution is conducive to analyze the crystallization kinetics. In situ characterizations are powerful tools to extract real-time structural information, where the in situ optical spectrum and X-ray scattering are frequently utilized with customized film-forming setup. In the following paragraph, we briefly summarize various common measurements, such as ultraviolet visible absorption spectroscopy (UV-vis) absorption spectra, photoluminescence (PL), grazing-incidence wide-angle X-ray scattering (GIWAXS), and grazing incidence small-angle X-ray scattering (GISAXS). Then, we emphasize their significance and refer to classic examples to elucidate the information derived from each in situ characterization technique.