Nanoscale Mapping of Charge-Trap-Induced Localized Bandgap Variations in Perovskite Solar Cell Structures via Wavelength-Dependent Noise Microscopy

We report the nanoscale mapping of charge-trap-induced local bandgap variations in an organic–inorganic halide perovskite film within a solar cell structure. For mapping, a conducting probe scanned the perovskite film surface under monochromatic illumination at different wavelengths to simultaneously map wavelength-dependent photocurrents and electrical noise. The measured maps were analyzed further to obtain the spatial distributions of photoconductive properties, such as photocurrent (I_pc), short-circuit current (I_sc), and charge trap density (N_eff), in the film. Interestingly, both the photocurrent and short-circuit current exhibited negative correlations with trap density following distinct power-law relationships. Importantly, a local bandgap (E_g) map was obtained from wavelength-dependent photocurrent maps by applying the Tauc plot method with local external quantum efficiencies (EQE) at different wavelengths, revealing spatial variations across the perovskite film. Quantitative analysis revealed a correlation between variations of bandgap and effective trap density following ΔE_g ∝ N_eff^–0.01, indicating that localized traps near the band edges effectively reduce the bandgaps. Our strategy enables direct mapping of nanoscale photoconductive properties and their quantitative correlations, providing a powerful tool for both fundamental research and practical applications in optoelectronic devices.