Molecule-Induced p-Doping in Perovskite Nanocrystals Enables Efficient Color-Saturated Red Light-Emitting Diodes.

Color-saturated red light-emitting diodes (LEDs) with emission wavelengths at around 620-640 nm are an essential part of high-definition displays. Metal halide perovskites with very narrow emission linewidth are promising emitters, and rapid progress has been made in perovskite-based LEDs (PeLEDs); however, the efficiency of the current color-pure red PeLEDs-still far lags behind those of other-colored ones. Here, a simple but efficient strategy is reported to gradually down-shift the Fermi level of perovskite nanocrystals (NCs) by controlling the interaction between NCs and their surface molecular electron acceptor-benzyl iodide with aromatic rings-and realize p-doping in the color-saturated 625 nm emitting NCs, which significantly reduces the hole injection barrier in devices. Besides, both the luminescence efficiency and electric conductivity of perovskite NCs are enhanced as additional advantages as the result of surface defects passivation. As a result, the external quantum efficiency for the resulting LED is increased from 4.5% to 12.9% after benzyl iodide treatment, making this device the best-performing color-saturated red PeLED so far. It is further found that the hole injection plays a more critical role than the photoluminescence efficiency of perovskite emitter in determining the LED performance, which implies design principles for efficient thin-film planar LEDs.

Interfacial Regulation toward Efficient CsPbBr3 Quantum Dot-Based Inverted Perovskite Light-Emitting Diodes.

Inverted perovskite light-emitting diodes (PeLEDs) based on quantum dots (QDs) are some of the most promising candidates for next-generation lighting and display applications. Due to the strong fluorescence quenching caused by zinc oxide, high performance in such inverted devices remains challenging. Here, we report an efficient inverted green CsPbBr3 QDs LED using an emitting buffer layer. Ultrathin CsPbBr3 QD emitters act as the buffer layer to reduce the interface luminescence quenching reaction at the ZnO/upper emitting layer interface, increasing the probability of exciton recombination within the emissive layer and regulating the charge transport, leading to effective carrier recombination. The resulting device exhibits an external quantum efficiency of 13.1%, enhanced by about 4.7 times compared with that without a buffer layer device. This work provides a path to fabricating high-performance inverted PeLEDs.

Light-emitting field-effect transistors with EQE over 20% enabled by a dielectric-quantum dots-dielectric sandwich structure.

Emerging quantum dots (QDs) based light-emitting field-effect transistors (QLEFETs) could generate light emission with high color purity and provide facile route to tune optoelectronic properties at a low fabrication cost. Considerable efforts have been devoted to designing device structure and to understanding the underlying physics, yet the overall performance of QLEFETs remains low due to the charge/exciton loss at the interface and the large band offset of a QD layer with respect to the adjacent carrier transport layers. Here, we report highly efficient QLEFETs with an external quantum efficiency (EQE) of over 20% by employing a dielectric-QDs-dielectric (DQD) sandwich structure. Such DQD structure is used to control the carrier behavior by modulating energy band alignment, thus shifting the exciton recombination zone into the emissive layer. Also, enhanced radiative recombination is achieved by preventing the exciton loss due to presence of surface traps and the luminescence quenching induced by interfacial charge transfer. The DQD sandwiched design presents a new concept to improve the electroluminescence performance of QLEFETs, which can be transferred to other material systems and hence can facilitate exploitation of QDs in a new type of optoelectronic devices.

Solution-Processed Double-Junction Quantum-Dot Light-Emitting Diodes with an EQE of Over 40.

Despite the rapid development in quantum-dot light-emitting diodes (QD-LEDs) with a single junction, it remains a big challenge to make tandem QD-LEDs with high performance. Here, we report solution-processed double-junction tandem QD-LEDs with a high external quantum efficiency of 42.2% and a high current efficiency of 183.3 cd A-1, which are comparable to those of the best vacuum-deposited tandem organic LEDs. Such high-efficiency devices are achieved by interface engineering of fully optimized single light-emitting units, which improves carriers' transport/injection balance and suppresses exciton quenching induced by ZnO, and design of an effective interconnecting layer consisting of poly(4-butylphenyl-diphenylamine) (poly-TPD)-mixed poly(9-vinylcarbazole) (PVK)/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate/polyethylenimine ethoxylated-modified ZnO.