Highly Efficient and Stable Green Quantum Rod LEDs Enabled by Material and Charge Injection Engineering

Nanocrystal-based light-emitting diodes (LEDs) are a promising technology for the next generation of flexible and large-area displays, offering high brightness, tunable narrow emission, and high display contrast. Although internal quantum efficiency (IQE) has reached unity, the external quantum efficiency (EQE) of LEDs utilizing spherical quantum dots (QDs) is limited by low light outcoupling efficiency (η_out). A promising approach to improve η_out is using horizontal alignment of nanocrystals' transition dipole moments, such as aligned quantum rods (QRs), which provide directional light emission. Though the IQE for QRs has recently improved significantly, creating efficient and bright green-emitting QRs (515-560 nm) remains a big challenge, which is essential for full-color display applications. In this study, a uniform and highly bright green-emitting CdSe/Zn_xCd_1-xS QRs of gradient shell structure are synthesized with minimized shell thickness and reduced Zn content, coupled with shorter organic ligands to reduce the energy barriers and enhance carriers injection. The electron leakage current at the interface between the polymeric hole transport layer (HTL) and QRs is the primary factor limiting the QRLED's performance. HTL with a higher energy offset is employed to prevent electron leakage at the organic/inorganic interface. Furthermore, is developed a bilayer HTL that enhances hole injections while minimizing electron leakage, thereby improving charge balance. The resulting QRLEDs demonstrate a record-high efficiency, with an EQE of 24%, current efficiency (CE) of 89 cd A^-1, and maximum brightness (L_max) exceeding 500k cd m^{- 2}. Additionally, they exhibited an extended operational T₅₀ lifetime of over 22k h at 100 cd m^{- 2}, making them well-suited for high-color-gamut display and lighting applications.