Metal halide perovskites have emerged as promising materials for solar cells and other optoelectronic devices, due to their outstanding optical and electronic properties. To optimize device performance and minimize degradations effects under operation, a detailed understanding of the optoelectronic and structural properties at the micro- and nanoscale is required.

In this study, we utilize cathodoluminescence spectroscopy (CL) to carry out these studies. In CL, a high-energy electron beam (5-30 keV) in a scanning electron microscope (SEM) is raster-scanned over the surface and the light emission is detected and analysed. We investigate the CL emission from polycrystalline CsPbBr₃ films and correlate 2D CL maps with high spatial resolution with the surface morphology at the nanoscale. We find that the CL intensity is significantly reduced at the polycrystalline perovskite film's grain boundaries, hinting at reduced optical quality in these regions.

We then utilise optical near-field simulations to simulate the CL emission intensity across the surface, taking into account the surface morphology around the grain boundaries and the electron-sample interaction distribution beneath the surface. We use surface profiles measured with AFM as input for the simulations. We find that the experimental CL line profiles closely resemble the simulations, indicating that the nano- and microscale surface morphology strongly affects the light outcoupling, leading to reduced CL emission collected from the grain boundaries. As a result, we conclude that the morphological effect on light outcoupling dominates the variation in the detected CL signal.

Our work shows that CL spectroscopy is a powerful tool to study opto-electronic properties of perovskite and other semiconductor materials at the nano- and micro-scale. At the conference we will present additional data comparing simulations with experiments with varying probing depths by varying the electron beam energy. Using Monte Carlo simulations of the electron-sample interaction volume enables estimation of the carrier diffusion length near the grain boundaries. In a further advanced analysis, considering the calculated local density of states near the corrugated surfaces, we use CL spectroscopy to probe the emission quantum efficiency of perovskite films at deep sub-wavelength spatial resolution.