Lead-based halide perovskites, particularly CsPbBr₃, have emerged as promising candidates for optoelectronic applications owing to their tunable bandgap, high absorption coefficient, cost-effectiveness, and robustness against defects. This study employs Electron Energy Loss Spectroscopy (EELS) within a Transmission Electron Microscopy (TEM) framework to unravel the electronic and structural characteristics of CsPbBr₃, with a primary focus on local bandgap estimate.

Utilising the python-based software Hyperspy [1] for EELS spectrum analysis, we delve into the complexity of CsPbBr₃'s electronic properties. In EELS, high-energy (normally 30-300 keV) electrons pass through the sample and are then dispersed according to the energy they have lost, resulting in a spectrum that offers detailed insights into the local electronic structure, including width and nature of the of bandgap, which are critical parameter for optoelectronics.

The computational analysis, demonstrated here, extracts key information about the sample. The dielectric function is determined using both the refractive index and the Kramers-Kronig method [2]. The dielectric function is then employed to retrieve information about the Cherenkov radiation contribution [3]. Thickness calculations are obtained directly from the hypermap of the sample by estimating the electron mean free path from the EELS spectrum. Finally, the bandgap is evaluated using two different approaches: one based on linear fits, similarly to the Tauc plot procedure often used in optics, and one identifying the inflection point of the signal.

The results highlight small local variations in bandgap values, ranging between 2.27eV and 2.28eV in estimates that are consistently robust across diverse methodological approaches. This work demonstrates the potential for EELS to extract crucial electronic information from inorganic halide perovskites, emphasising its potential for advancing our comprehension of this class of materials. The findings also highlight the need for meticulous analysis to confirm the stability and coherence of the methodology. As the focus remains on utilising EELS to uncover detailed electronic insights, further investigations are warranted to enhance the technique's reliability and robustness. This study contributes to the ongoing quest for a comprehensive understanding of CsPbBr₃'s electronic properties, specifically highlighting the utility of EELS to understand local properties on the nanoscale and direct the engineering of perovskite-based films and devices.