Interfaces play a pivotal role in governing the efficiency and long-term stability of solar cells. While device performance is typically evaluated using macroscopic electrical and photophysical measurements, these bulk characteristics emerge from complex microscopic processes occurring at buried interfaces, where structural, chemical, and electronic properties converge. Defects, carrier transport pathways, and interfacial chemical reactions—particularly under operational stimuli such as illumination, electrical bias, and ambient exposure—critically determine device functionality. This interplay is especially pronounced in metal halide perovskites, whose soft and dynamic lattice renders defect and interfacial processes highly responsive and metastable.

We have introduced Correlation Clustering Imaging (CLIM),[1] a noninvasive microscale functional imaging technique that exploits intrinsic photoluminescence (PL) dynamics under continues excitation to probe these processes in space and time. The foundation of CLIM lies in the PL blinking phenomenon observed in sub-micrometer and even larger individual perovskite crystals, first reported in 2015[2] and subsequently studied in depth.[3][4] This blinking behavior originates from so-called supertraps—metastable nonradiative recombination centers that reversibly switch between active and inactive states. Such defect metastability, or the non-persistent presence of defect states, is now recognized as a key factor underlying the remarkably low nonradiative energy losses in metal halide perovskite materials and devices. CLIM generalizes this concept to extended films and operating devices by analyzing spatial correlations in PL fluctuations using wide-field fluorescence microscopy.

Applied to high-quality perovskite thin films, CLIM visualizes the polycrystalline grain structure with high fidelity, producing images closely resembling scanning electron microscopy results while remaining entirely noninvasive. Correlative CLIM–SEM analysis reveals how structural heterogeneities manifest as spatial variations in defect-mediated emission dynamics.

Strikingly, when the same materials are integrated into complete solar cell architectures, the PL dynamics change fundamentally. Under short-circuit and operating conditions, both the amplitude of PL fluctuations and the spatial extent of correlated regions increase markedly, with correlation lengths extending up to ~10 μm compared to ~2 μm in thin films. We propose that these extended correlated regions arise from dynamically evolving charge extraction pathways at transport-layer interfaces, which act as transient PL quenching channels sensitive to applied bias.[1]

By directly linking defect metastability and interfacial dynamics to nonradiative recombination losses, CLIM provides unprecedented insight into the microstructure–function relationship in dynamic optoelectronic materials.[1][5] Owing to its simplicity and operando compatibility, CLIM offers a powerful route to monitor material evolution during fabrication and to rationally engineer interfaces for improved efficiency and stability in next-generation optoelectronic devices.