Disentangling\nthe Optoelectronic Behavior of Lead\nIodide Governed by Two-Dimensional Electron Confinement

We present a joint\nexperimental and theoretical study for complete\nspectroscopic characterization and optoelectronic properties of lead\niodide. Experimentally, we combine X-ray diffraction experiments to\nelucidate the structure with photoelectron spectroscopy to explore\nits electronic structure. Computationally, simulations are performed\nin the frame of density functional theory. We show that PbI<sub>2</sub> presents a two-dimensional layered structure and exhibits a large\ntransient photocurrent effect under visible light illumination, which\nare compatible with the surface photovoltage scenario. The transient\nphotocurrent has an extremely long lifetime: when the sample is lightened\nwith visible light, it shows very long relaxation times and, consequently,\nhuge charge carrier diffusion lengths. We explain this anomalous behavior\nwith the slow carrier mobility of holes and electrons caused by the\n2D electron confinement in the layered material. Our results can be\nused as a simple model for understanding the optoelectronic properties\nof more complex 2D hybrid perovskites.