Synthesis of 2D perovskite crystals via progressive transformation of quantum well thickness

Two-dimensional (2D) multilayered halide perovskites have emerged as a platform for understanding organic–inorganic interactions, tuning quantum confinement effects and realizing efficient and durable optoelectronic devices. However, reproducibly synthesizing 2D perovskite crystals with a perovskite-layer thickness (quantum well thickness, n-value) >2 using existing crystal growth methods is challenging. Here we demonstrate a synthetic method, termed kinetically controlled space confinement, for the growth of phase-pure Ruddlesden–Popper and Dion–Jacobson 2D perovskites. Phase-pure growth is achieved by progressively increasing the temperature (for a fixed time) or the crystallization time (at a fixed temperature), which allows for control of the crystallization kinetics. In situ photoluminescence spectroscopy and imaging suggest that the controlled increase in n-value (from lower to higher values of n = 4, 5 and 6) occurs due to intercalation of excess precursor ions. Based on 250 experimental data sets, phase diagrams for both Ruddlesden–Popper and Dion–Jacobson perovskites have been constructed to predict the growth of 2D phases with specific n-values, facilitating the production of 2D perovskite crystals with desired layer thickness. Synthesizing phase-pure, higher-quantum-well thickness (n) 2D halide perovskites is challenging. Now, a general method, termed kinetically controlled space confinement, to synthesize 2D perovskites is reported. Transformation from low n-values to high n-values is achieved by tuning the temperature or time of crystallization.