Single molecule spectroscopy has tremendously impacted every field in which the technique was applied, ranging from catalysis over plasmonics, polymer physics, biophysics to cell biology and DNA sequencing. Furthermore, single molecule techniques have allowed researchers to push the resolution of fluorescence microscopy past the diffraction limit, based on characteristic single molecule intermittence of fluorescence. In this presentation, I will give an overview of how recent single molecule experiments and development of new microscopy modalities in my laboratory have been impacted by material science and how these experiments have been driving developments in material science, with a focus on our perovskite research. Unlike conventional semiconductor materials, metal halide perovskites (MHP) possess soft and ionic crystal structures leading to several unique features like facile ion migration, self-healing, elasticity, and memory. Within this dynamic system, external stimuli like high photon doses, electron beams, electrical bias, and mechanical stress induce structural changes and alter associated optoelectronic properties. Therefore, it is crucial to investigate the structure-function relationship in these materials, especially in operational devices like solar cells, where traditional methods such as scanning electron microscopy fall short due to the layered structure. Moreover, electron and x-ray-based analytical techniques are often invasive altering the material properties.

To address these challenges, we developed Correlation Clustering Imaging (CLIM), a novel noninvasive method that utilizes photoluminescence fluctuations to reveal contrasts associated with defect dynamics in semiconductor materials. CLIM images of perovskite thin films show one-to-one matching with the grains in SEM images captured at the same locations. Particularly noteworthy is the application of CLIM to high-efficiency photovoltaic devices, uncovering previously unnoticed photoluminescence intensity fluctuations that strongly depend on the device's operational regime. Statistical analysis of these intensity fluctuations provides insights into the type of metastable defects responsible for fluctuating non-radiative recombination processes.

The insights gained from CLIM contribute to a deeper understanding of device efficiency, structure, and degradation, which are crucial for the rational engineering of the next generation of devices. The broad applicability of CLIM, requiring only a standard wide-field microscope and our user-friendly, open-source algorithm, positions it as an important new tool for material chemists, engineers, and device scientists [1,2].