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Solution-processed optoelectronic and electronic devices are attractive owing to the potential for low-cost fabrication of large-area devices and the compatibility with lightweight, flexible plastic substrates. Solution-processed light-emitting diodes (LEDs) using conjugated polymers or quantum dots as emitters have attracted great interest over the past two decades (1,2). However, the overall performance of solution-processed LEDs (2-5)--including their efficiency, efficiency roll-off at high current densities, turn-on voltage and lifetime under operational conditions--remains inferior to that of the best vacuum-deposited organic LEDs (6-8). Here we report a solution-processed, multilayer quantum-dot-based LED with excellent performance and reproducibility. It exhibits colour-saturated deep-red emission, sub-bandgap turn-on at 1.7 volts, high external quantum efficiencies of up to 20.5 per cent, low efficiency roll-off (up to 15.1 per cent of the external quantum efficiency at 100 mA [cm.sup.-2]), and a long operational lifetime of more than 100,000 hours at 100 cd [m.sup.-2], making this device the best-performing solution-processed red LED so far, comparable to state-of-the-art vacuum-deposited organic LEDs (2-8). This optoelectronic performance is achieved by inserting an insulating layer between the quantum dot layer and the oxide electron-transport layer to optimize charge balance in the device and preserve the superior emissive properties of the quantum dots. We anticipate that our results will be a starting point for further research, leading to hig-hperformance, all-solution-processed quantum-dot-based LEDs ideal for next-generation display and solid-state lighting technologies., Quantum dots are solution-processable semiconductor nanocrystals (9-11) that promise size-tunable emission wavelengths, narrow emission linewidths, near-unity-photoluminance quantum yield and inherent photophysical stability. As inorganic crystalline emission centres, quantum dots are [...]

The surface defects of solution-processed ZnO films lead to various intragap states. When the solution-processed ZnO films are used as electron transport interlayers (ETLs) in inverted organic solar cells, the intragap states act as interfacial recombination centers for photogenerated charges and thereby degrade the device performance. Here, a simple passivation method based on ethanedithiol (EDT) treatment is demonstrated, which effectively removes the surface defects of the ZnO nanocrystal films by forming zinc ethanedithiolates. The passivation by EDT treatment modulates the intragap states of the ZnO films and introduces a new intragap band. When the EDT-treated ZnO nanocrystal films are used as ETLs in inverted organic solar cells, both the power conversion efficiency and stability of the devices are improved. The control studies show that the solar cells with EDT-treated ZnO films exhibit reduced charge recombination rates and enhanced charge extraction properties. These features are consistent with the fact that the modulation of the intragap states results in reduction of interfacial recombination as well as the improved charge selectivity and electron transport properties of the ETLs. It is further demonstrated that the EDT treatment-based passivation method can be extended to ZnO films deposited from sol-gel precursors. [ABSTRACT FROM AUTHOR]

A method to deposit NiOx thin films by employing combustion reactions is reported and a low processing temperature of 175 °C is demonstrated. The resulting NiOx films exhibit high work functions, excellent optical transparency, and flat surface features. The NiOx thin films are employed as hole‐transport interlayers in organic solar cells and polymer light‐emitting diodes, exhibiting superior electrical properties. [ABSTRACT FROM AUTHOR]

Solution‐processed oxide thin films are actively pursued as hole‐injection layers (HILs) in quantum‐dot light‐emitting diodes (QLEDs), aiming to improve operational stability. However, device performance is largely limited by inefficient hole injection at the interfaces of the oxide HILs and high‐ionization‐potential organic hole‐transporting layers. Solution‐processed NiOx films with a high and stable work function of ≈5.7 eV achieved by a simple and facile surface‐modification strategy are presented. QLEDs based on the surface‐modified NiOx HILs show driving voltages of 2.1 and 3.3 V to reach 1000 and 10 000 cd m−2, respectively, both of which are the lowest among all solution‐processed LEDs and vacuum‐deposited OLEDs. The device exhibits a T95 operational lifetime of ≈2500 h at an initial brightness of 1000 cd m−2, meeting the commercialization requirements for display applications. The results highlight the potential of solution‐processed oxide HILs for achieving efficient‐driven and long‐lifetime QLEDs. [ABSTRACT FROM AUTHOR]

Solution-processed NiO x thin films have been applied as hole-injection layers (HILs) in quantum-dot light-emitting diodes (QLEDs). The commonly used NiO x HILs are prepared by the precursor-based route, which requires high annealing temperatures of over 275 °C to in situ convert the precursors into oxide films. Such high processing temperatures of NiO x HILs hinder their applications in flexible devices. Herein, we report a low-temperature approach based on Cu-modified NiO x (NiO x -Cu) nanocrystals to prepare HILs. A simple post-synthetic surface-modification step, which anchors the copper agents onto the surfaces of oxide nanocrystals, is developed to improve the electrical conductivity of the low-temperature-processed (135 °C) oxide-nanocrystal thin films. In consequence, QLEDs based on the NiO x -Cu HILs exhibit an external quantum efficiency of 17.5 % and a T 95 operational lifetime of ∼2,800 h at an initial brightness of 1,000 cd m -2 , meeting the commercialization requirements for display applications. The results shed light on the potential of using NiO x -Cu HILs for realizing high-performance flexible QLEDs., (© 2021 Wiley-VCH GmbH.)