Control of Lateral Assembly and Vertical Stacking in Spin-Coated Lead Halide Perovskite Nanocrystal Films for Enhanced Photoluminescence Efficiency

Lead halide perovskite (LHP) nanocrystals (NCs) hold great promise for advanced photonic and optoelectronic applications due to their near-unity photoluminescence (PL) quantum efficiency, narrow emission line width, and tunable spectral wavelength. However, the fabrication of spatially uniform, ultrathin films over a large-scale device area has been impeded by the instability of LHP NCs toward heat and polar solvents. Here, we demonstrate a feasible strategy that enables not only the assembly of various LHP NCs for constructing two-dimensional (2D) films but also precise controllability of multilayer films over large-scale areas. The key process is standard but extremely careful sample preparation, such as purification of the NCs, control of the concentration of the NC dispersion used for spin-coating, and vacuum drying between repetitive spin-coating cycles. We experimentally confirmed that these optimized methodologies promote strong inter-NC interactions, leading to the lateral self-assembly of NCs and subsequently enabling vertical stacking within multilayer NC films. Furthermore, by coupling with a reflective substrate and utilizing a multilayer NC film, the PL intensity of the LHP NC 2D film is significantly enhanced through constructive interference when the number of layers is adequately selected to stimulate optical oscillation, similar to Fabry-Pérot resonance. We believe that this work could lead to additional opportunities for the development of advanced LHP devices and offer a practical physical platform for exploring light-matter interactions.