As the concerns about using cadmium-based quantum dots (QDs) in display are growing worldwide, InP QDs have drawn much attention in quantum dot light-emitting diodes (QLEDs). However, pure blue InP based QLED has been rarely reported. In this work, first of all, pure blue InP/ZnS QDs with emission wavelength of 468 nm and quantum yield of 45% are synthesized. Furthermore, zinc oleate and STOP are used as precursors to epitaxially grow the second ZnS shell. The residual zinc stearate reacted with STOP to form ZnS shell, which increased the thickness and stability of QDs. Moreover, as the residual precursor of zinc stearate is removed, the current density increased from 13 mA cm −2 to 121 mA cm −2 at 8 V for the hole only device. External quantum efficiency increased from 0.6% of InP/ZnS QLED to 1.7% of InP/ZnS/ZnS QLED.

Colloidal nanoplatelets (NPLs) are an emerging semiconductor nanocrystal in the display community due to their ultranarrow emission linewidth. Herein, an ultrapure green emitting nanocrystal light‐emitting diode (LED) based on four‐monolayer CdSe/CdS core/crown NPLs is developed. By applying the nonstacked nanoplates, the nonradiative energy transfer in the NPLs film is successfully suppressed. The nonstacked NPL‐LEDs with pure green emission of 521.5 nm exhibit a low turn‐on voltage of 2.1 V, a maximum luminance of 22 400 cd m−2, a peak external quantum efficiency (EQE) of 2.16%, which is a sixfold enhancement comparing to the stacked NPL‐LED (EQE = 0.34%). This work demonstrates the potential of core/crown NPLs for ultrawide color gamut displays.

Improving the stability of inkjet‐printed quantum dot light emitting diodes (QLEDs) is critical for the technology to become commercially viable. The major obstacle is the compromise between the printability of the ink system and the functionality of the carrier transport layers. Here, a ternary ink system consisting of octane, 1‐cyclohexyl‐ethanol, and n‐butyl acetate is reported, which solves the erosion between the printed quantum dot ink and the underneath hole transport layer. A gradient vacuum post‐treatment is developed to accompany the ternary ink system with gradient vacuum pressures, which is helpful in forming a uniform printing layer. Based on both technologies, the inkjet‐printed R/G/B QLEDS are fabricated with high resolution patterns, showing high efficiencies and stabilities. The external quantum efficiency of R/G/B devices is 19.3%, 18.0%, and 4.4%, respectively. Correspondingly, the half operating lifetime is up to 25 178 h @ 1000 cd m−2, 20 655 h @ 1000 cd m−2, and 46 h @ 100 cd m−2, respectively. The improvements in the ink engineering and post‐treatment in this study have taken the efficiency and stability of the devices to a higher level and confirm the application prospects of printed QLEDs in the display industry.

The phenomenon of positive aging has been frequently reported in quantum dot light-emitting diodes (QLEDs). However, the root cause for this phenomenon remains illusive. On the other hand, the commonly used electron transport material in QLEDs, ZnMgO, has been extensively studied as a resistive switching material. In this work, we found that the ZnMgO nano-particle film used in QLEDs showed a clear resistive switching effect. It is, thus, reasonable to relate the resistive switching mechanism of ZnMgO to the aging characteristics of QLED devices. We found that during the first stage of QLED aging, the efficiency of the QLED was improved due to the migration of off-lattice ions and formation of conductive filaments in the ZnMgO layer. Subsequently, as active oxygen ions migrated to the interface between quantum dots and ZnMgO, the barrier for electron transport increased due to the oxidation of quantum dots. At the same time, the conductive filaments were gradually fused due to the continuous external electric field. As a result, the performance of QLED devices continuously deteriorated.

Enhanced hole injection is essential to achieve high performance in perovskite light-emitting diodes (LEDs). Here, a strategy is introduced to enhance hole injection by an electric dipole layer. Hopping theory demonstrates electric dipoles between hole injection layer and hole transport layer can enhance hole injection significantly. MoO3 is then chosen as the electric dipole layer between PEDOT:PSS (hole injection layer) and PVK (hole transport layer) to generate electric dipoles due to its deep conduction band level. Theoretical results demonstrate that strong electric fields are produced for efficient hole injection, and recombination rate is substantially increased. Capacitance-voltage analyses further prove efficient hole injection by introducing the electric dipole layer. Based on the proposed electric dipole layer structure, perovskite LEDs achieve a high current efficiency of 72.7 cd A−1, indicating that electric dipole layers are a feasible approach to enhance perovskite LEDs performance.