Correlation Clustering Imaging: A method for Functional Mapping of Semiconductor materials and photovoltaic devices in operando

Understanding the relationship between the active material's structure and function in operational devices is key for the rational engineering of the next generation of devices. However, this has proven elusive due to the invasiveness of structural characterization methods and their inability to penetrate the multi-layered device. Here, we introduce a Correlation Clustering Imaging Method (CLIM) based on photoluminescence microscopy. CLIM offers insights into structural and functional aspects related to carrier transport, defects, and recombination losses in operational photovoltaic devices. Our study reveals the presence of "blinking" phenomena in high-quality semiconductor films and their corresponding devices. CLIM demonstrates that highly correlated clusters correspond precisely to grain structures of perovskite layer on glass observed with SEM. Importantly, we find that the perovskite layer in photovoltaic devices exhibits predominant blinking during specific operational conditions. The correlated regions within devices are notably larger than those on bare substrate, indicating different microstructures likely caused by the transport layer at the interface. CLIM's contrast opens new possibilities in optical microscopy for functional imaging of materials and in-operando device, enabling the rational design and optimization of high-efficiency photovoltaic devices.