Small-Molecule-Assisted Growth of Perovskite Nanoplatelets for Efficient Light-Emitting Diodes

Controlling the crystallization processes and energy-level alignment in perovskite emitters is crucial for realizing high-performance light-emitting diodes (LEDs) because these factors directly govern the radiative recombination efficiency. Here, we introduce benzylphosphonic acid (BPA) as a directive molecular template that directs the morphological evolution of perovskite materials, first forming two-dimensional (2D) nanoplatelets (NPLs), which then serve as structural scaffolding for the subsequent formation of a compact, pinhole-free film. Density functional theory (DFT) simulations reveal that BPA not only exhibits a strong binding affinity to the perovskite precursor, but also possesses the highest occupied molecular orbital (HOMO) level optimally aligned with the valence band maximum (VBM) of CsPbBr₃. This dual capability enables BPA to function both as a crystal-regulating agent guiding NPL growth and as an effective electron-blocking interlayer at the hole transport interface. The resulting perovskite films exhibit enhanced crystallinity and photoluminescence quantum yield. Consequently, BPA-assisted green PeLEDs achieve a remarkable peak external quantum efficiency (EQE) of 26.42% and a maximum luminance of ∼50,100 cd m^-2. Notably, this approach is universally applicable, improving the EQE of blue-emitting CsPbCl_1.5Br_1.5 PeLEDs from 3.29% to 10.24%. These findings highlight the promise of molecule-level interfacial engineering in perovskite morphology control and device performance.