Ligand-induced self-assembly of twisted two-dimensional halide perovskites

Two-dimensional (2D) halide perovskites (HPs) are now an emerging materials system that exhibits intriguing optoelectronic functionalities. Conventionally, they have been synthesized with linear and/or planar molecular spacers, rendering nominal modifications in optoelectronic properties. In contrast, lower dimensional HPs (0D and 1D) have been accommodating to the incorporation of bulky molecular spacers, leaving fundamental insights to remain elusive in their application for unconventional 2D HP structures. Herein, by implementing a high-throughput autonomous exploration workflow, crystallization behaviors of 2D HPs based on bulky 3,3-diphenylpropylammonium (DPA) spacer are comprehensively explored. Counterintuitive to the conventional HP chemistry, synthesis of 2D DPA2PbI4 HP is indeed feasible when the steric hindrance is mediated by minute incorporation of 3D HPs. Furthermore, a Moiré superlattice is observed from the DPA2PbI4 flakes, indicating the spontaneous formation of twisted stacks of 2D HPs – the first time to the best our knowledge. We hypothesize that the unconventional van der Waals surface of DPA2PbI4 facilitates the self-assembly of the twisted stacks of 2D HPs. This work exemplifies how high-throughput experimentation can discover unconventional material systems where the synthetic principle lies beyond the conventional chemical intuition. Furthermore, these findings provide hints on how to ‘chemically’ manipulate the twist stacking in 2D HPs, thus rendering a straightforward way for bespoke realization of functionalities in exotic materials systems via bottom-up approach.