The Role of Edge States for Charge Carrier Separation in <i>n</i> = 1 2D Perovskites

Optoelectronic devices based on 2D perovskites exhibit efficient charge carrier separation, despite their large excitonic binding energy. For 2D perovskites with n ≥ 2, edge states facilitate exciton dissociation, with n giving the number of inorganic layers. However, similar states have not been shown for n = 1 2D perovskites. Here, we use correlated spatially resolved photocurrent and photoluminescence (PL) measurements to reveal an increased photocurrent along the grain boundaries compared to the grain interiors of BA2PbI4 thin films, which we attribute to edge states. Detected at 90° relative to the excitation, the PL emission of these states is red-shifted by 70 meV compared to the main excitonic emission. It is found that the emission intensity correlates with the total photocurrent in temperature-dependent measurements, clearly demonstrating the involvement of these states in the process of charge carrier separation. We identified the edge states as electron traps and gained insights into the charge carrier transport within the perovskite layer.