Deterministic Nucleation of Nanocrystal Superlattices on 2D Perovskites for Light-Funneling Heterostructures

Semiconductor heterostructures that combine components with different dimensionalities provide an interesting avenue to manipulate the physical properties of the resulting material. Two-dimensional lead halide perovskites crystallize as flat microcrystals and have efficient in-plane exciton mobility, while perovskite nanocrystals are efficient emitters with a tunable bandgap that can self-assemble into microscopic superlattices. However, combining such intricate architectures into heterostructures has been challenging due to the mismatch in solubility and difficult transfer procedures. Here, we realize heterostructures where CsPbBr₃ nanocrystal superlattices are deterministically grown along the faces of PEA₂PbBr₄ 2D layered perovskite microcrystals. The growth can either be limited to the lateral faces of the microcrystals and result in core-crown epitaxial heterostructures, or extended to the vertical direction leading to core-shell-like structures. We demonstrate that these heterostructures can be employed as efficient light-harvesting systems. In fact, energy can be transferred from the 2D microcrystal domain to the superlattices, enabling switching between linear and nonlinear carrier recombination regimes by tuning the excitation fluence. Moreover, by exploiting the lifetime shortening of CsPbBr₃ nanocrystal emission upon sample cooling, we ensure that energy transfer occurs after the biexcitonic and single-excitonic decays of the nanocrystals, effectively extending the radiative life time of the superlattices.