High-Throughput Exploration on the Phase Growth Behaviors in Quasi-2D Formamidinium-Based Perovskites

Low-dimensional quasi-two-dimensional (2D) perovskites – a mixed structure of 2D and three-dimensional (3D) perovskite lattice – are now the leading materials platform for the demonstration of functional optoelectronics. The dimensional confinements of perovskite lattice by molecular spacer cations and the resulting quantum-well structures bestow their unique functionalities including chemical robustness and strong light-emission properties. Despite its versatility, little has been known on the principle of phase control in quasi-2D perovskites. Herein, by using a robot-based high-throughput automated synthesis platform, we explore the phase formation behaviors of quasi-2D phenethylammonium-formamidinium perovskite system in a wide range of 2D (PEA₂PbI₄):3D (FAPbI₃) compositions. We observe that, in contrast to the stoichiometric consideration, incorporation of only 1% of the 3D component provides substantial emergence of n=2 2D phase, which is prominent up to the 3D ratio of 92%; after this composition, 3D-like phases that are more stable than the pristine 3D FAPbI₃ mainly emerge. Coupled with hyperspectral cathodoluminescence microscopy, we uncover that thermal annealing is necessary for thin film fabrication of quasi-2D perovskites, but concurrently involves the emergence of PbI₂. Our work provides practical insights into the fundamental principles in 2D perovskite phase control, further benefitting the functionalities of novel materials systems towards sustainable device applications.