Terminations Determine Energy-Level Alignment of Perovskite Buried Interfaces.

The "substrate-effect", where the semiconduction type of perovskite changes according to that of the substrate is a widely-reported, but so far not fully understood phenomenon in the field of perovskite. The main challenge lies in the difficulty of probing and comprehending the electronic properties of perovskite buried interfaces. Here, through broadly investigating 20 buried interfaces formed between different perovskites and organic hole or electron transport materials (HTMs or ETMs), it is revealed that the substrate-effect originates from the distinct energy-level alignments at HTM or ETM substrates. Experimental and theoretical studies reveal that this difference stems from varying proportions of two perovskite terminations, which are determined by the interaction between substrates and perovskite crystals. With such mechanism, the semiconduction type of perovskite by controlling the proportion of surface terminations is successfully tuned. These findings provide new insights into optimizing device performance through termination engineering.