Inverted Device Engineering for Efficient and Bright Quantum Rod LEDs

Quantum dot light-emitting diodes (QD-LEDs) have approached the theoretical limit of external quantum efficiency (EQE) determined by outcoupling efficiency. To achieve further improvements, novel optical designs must be explored, such as constructing optical microcavities, utilizing light scattering, or tuning the orientation of transition dipole moments (TDM). This study reports advances in red rod-in-rod quantum rods (QRs) film that exhibits a high in-plane dipole orientation of 82%, achieved through shape-induced horizontal self-alignment. Also a critical issue is discovered: the carrier leakage through irregular quantum rod films, which hinders the EQE of quantum rod light-emitting diodes (QR-LEDs) and limits its competitiveness with QD-LEDs. An equivalent circuit model comprising two diodes clearly illustrates the impacts of the leakage current within conventional QR-LED structures. By transforming the QR-LEDs device structure, balanced carrier injection and suppressed leakage current are simultaneously enhanced, achieving a red QR-LEDs with a peak EQE of 31% and a peak brightness of 110 000 cd m^{- 2}. Additionally, these strategies are applied to green dot-in-rod QRs, demonstrating a peak EQE of 20.2% with ultra-high luminance of 250 000 cd m^{- 2}. This work is expected to pave the way for further improvements in the LED performance based on anisotropic nanocrystals.