Horizontally Aligned Dipole Emission through Solvent Controlled Fusing of Perovskite Nanocubes and Nanoplates into 1D Nanowires

Colloidal lead halide perovskite nanocrystals (NCs) are a promising class of materials for light-emitting applications, yet their external quantum efficiency in devices is limited by isotropic dipole orientations that suppress light outcoupling. Here, we demonstrate the effect of kinetic control over the morphology and effective transition dipole moment (TDMeff) orientation of CsPbBr3 NCs through the interplay of confinement effects and solvent-assisted self-assembly. By tuning the synthesis temperature (150–85 °C), we accessed nanocrystals with aspect ratios increasing from 1 (nanocubes) to 7.6 (nanoplatelets), enabling systematic control over anisotropy. Subsequent dispersion in low-polarity solvents (hexane, heptane, and octane) induced edge-to-edge fusion with slower-evaporating solvents producing elongated nanowires exceeding 1 μm in length. Using a first-order kinetic growth rate model, we estimated the maximum self-assembly times required for nanocrystals in each solvent to form nanowires >1 μm. Transmission electron microscopy (TEM) and photoluminescence (PL) confirmed that quantum confinement was preserved along the smallest dimension while lateral fusion drove anisotropy. The dipole orientation factor (φ) was tuned from 0.67 (isotropic cubes TDMeff 35°) to 0.86 (nanowires 22° ± 1°) by reducing reaction temperature and using slower-evaporating solvents. These results establish a direct correlation between aspect ratio and dipole alignment, providing a pathway to engineer horizontally oriented dipoles that enhance outcoupling efficiency. This solvent-controlled assembly framework offers a versatile route to optimize perovskite NCs for high-performance light-emitting diodes and photonic applications.