Bright and efficient quantum dot light-emitting diodes with double light-emitting layers

Stable and efficient pure blue quantum-dot LEDs enabled by inserting an anti-oxidation layer

The efficiency and stability of red and green quantum-dot light-emitting diodes have already met the requirements for commercialization in displays. However, the poor stability of the blue ones, particularly pure blue color, is hindering the commercialization of full-color quantum-dot light-emitting diode technology. Severe hole accumulation at the blue quantum-dot/hole-transport layer interface makes the hole-transport layer prone to oxidation, limiting the device operational lifetime. Here, we propose inserting an anti-oxidation layer (poly(p-phenylene benzobisoxazole)) between this interface to take in some holes from the hole-transport layer, which mitigates the oxidation-induced device degradation, enabling a T50 (time for the luminance decreasing by 50%) of more than 41,000 h with an initial brightness of 100 cd m-2 in pure blue devices. Meanwhile, the inserted transition layer facilitates hole injection and helps reduce electron leakage, leading to a peak external quantum efficiency of 23%.

Spectra Stable Quantum Dots Enabled by Band Engineering for Boosting Electroluminescence in Devices

The band level landscape in quantum dots is of great significance toward achieving stable and efficient electroluminescent devices. A series of quantum dots with specific emission and band structure of the intermediate layer is designed, including rich CdS (R-CdS), thick ZnSe (T-ZnSe), thin ZnSe (t-ZnSe) and ZnCdS (R-ZnCdS) intermediate alloy shell layers. These quantum dots in QLEDs show superior performance, including maximum current efficiency, external quantum efficiencies and a T₅₀ lifetime (at 1000 cd/m²) of 47.2 cd/A, 11.2% and 504 h for R-CdS; 61.6 cd/A, 14.7% and 612 h for t-ZnSe; 70.5 cd/A, 16.8% and 924 h for T-ZnSe; and 82.0 cd/A, 19.6% and 1104 h for R-ZnCdS. Among them, the quantum dots with the ZnCdS interlayer exhibit deep electron confinement and shallow hole confinement capabilities, which facilitate the efficient injection and radiative recombination of carriers into the emitting layer. Furthermore, the optimal devices show a superior T₅₀ lifetime of more than 1000 h. The proposed novel methodology of quantum dot band engineering is expected to start a new way for further enhancing QLED exploration.

Enhancing extraction efficiency of quantum dot light-emitting diodes introducing a highly wrinkled ZnO electron transport layer

Light extraction efficiency is crucial for achieving highly efficient and bright quantum dot light-emitting diodes (QLEDs), and current efforts toward introducing light outcoupling nanostructures always require complicated procedures. An extremely simple and efficient method to introduce light outcoupling nanostructures in the ZnO electron transport layer (ETL) is demonstrated by adopting a certain heating rate during the annealing process. The ultimate device exhibits a current efficiency of 9.1 cd/A, giving a 50% efficiency improvement compared to the control device with a flat ZnO ETL. This arises from the increased light extraction efficiency induced by random nanostructures formed on a wrinkled ZnO ETL, which could also be modulated by adjusting the heating rate during the annealing process. This study not only provides a simple and efficient method to introduce light outcoupling nanostructures, but also shows ample room for further performance enhancement of QLEDs with the guideline of light extraction.