Giant Shell Nanorods for High‐Efficiency and Low‐Roll‐Off Light‐Emitting Diodes

1D colloidal semiconductor nanorods (NRs) offer polarized emission and enhanced photon out-coupling efficiency for high-efficiency light-emitting diodes (LEDs). However, their practical application has been limited by severe efficiency roll-off at high current densities due to thin radial shells along the radial direction and the high aspect ratio that leads to random orientation during the fabrication of solution-processed films, which causes structural gaps, triggering leakage currents and ultimately exacerbating efficiency roll-off. Here, fatty acid is introduced to mitigate the c-axial growth induced by phosphonic acid in traditional NRs synthesis, while promoting radial shell growth, thereby forming giant-shell CdSe/CdZnSe/CdS/CdZnS NRs with an aspect ratio of ≈2.2. This design effectively alleviates electron leakage caused by random orientation in NR films, while minimizing interfacial defects and Auger recombination, achieving a near-unity PLQY. Consequently, NR-LEDs based on these NRs exhibit a peak external quantum efficiency (EQE) of 23.4% and a luminance of 289 000 cd m^- ². Significantly, this NR design greatly suppresses the EQE roll-off at high current density. Furthermore, the devices have a long T₉₅ lifetime of more than 10 000 h at a luminance of 1 000 cd m^- ². This material design strategy lays the foundation for realizing highly polarized NR-LEDs for efficient high-definition displays.