A “visible-blind” solution-processed UV photodetector is realized on the basis of colloidal ZnO nanoparticles. The devices exhibit low dark currents with a resistance >1 TΩ and high UV photocurrent ...efficiencies with a responsivity of 61 A/W at an average intensity of 1.06 mW/cm2 illumination at 370 nm. The characteristic times for the rise and fall of the photocurrent are <0.1 s and about 1 s, respectively. The photocurrent of the device is associated with a light-induced desorption of oxygen from the nanoparticle surfaces, thus removing electron traps and increasing the free carrier density which in turn reduces the Schottky barrier between contacts and ZnO nanoparticles for electron injection. The devices are promising for use in large-area UV photodetector applications.
The electrical, optical and other important properties of colloidal nanocrystals are determined mainly by the crystals’ chemical composition, size and shape. The introduction of specific dopants is a ...general approach of modifying the properties of such nanocrystals in well-controlled ways. Here we show that in addition to altering the atomic composition of the nanocrystals the introduction of specific dopants can also lead to dramatic changes in morphology. The creation of Mg-doped ZnO nanocrystals provides an excellent example of this procedure; depending on the molar ratio of dopant precursor in the reagents, doped nanocrystals with well-defined shapes, from tetrapods to ultrathin nanowires, which exhibit tunable optoelectronic properties, are obtained for the first time. We find that the Mg dopants play an important role in the primary growth stage, resulting in initial growth seeds having diverse crystallographic structures, which are critical for the generation of doped nanocrystals with different shapes. We demonstrate that this “greener” synthetic scheme can be extended to other dopant systems and provides an attractive and effective strategy for fabricating doped ZnO nanocrystals with interesting compositional and spatial complexity.
Abstract
Dynamic infrared emissivity regulators, which can efficiently modulate infrared radiation beyond vision, have emerged as an attractive technology in the energy and information fields. The ...realization of the independent modulation of visible and infrared spectra is a challenging and important task for the application of dynamic infrared emissivity regulators in the fields of smart thermal management and multispectral camouflage. Here, we demonstrate an electrically controlled infrared emissivity regulator that can achieve independent modulation of the infrared emissivity while maintaining a high visible transparency (84.7% at 400–760 nm). The regulators show high degree of emissivity regulation (0.51 at 3–5 μm, 0.41 at 7.5–13 μm), fast response ( < 600 ms), and long cycle life ( > 10
4
cycles). The infrared emissivity regulation is attributed to the modification of the carrier concentration in the surface depletion layer of aluminum-doped zinc oxide nanocrystals. This transparent infrared emissivity regulator provides opportunities for applications such as on-demand smart thermal management, multispectral displays, and adaptive camouflage.
Abstract
Quantum-dot light-emitting diodes promise a new generation of high-performance and solution-processed electroluminescent light sources. Understanding the operational degradation mechanisms ...of quantum-dot light-emitting diodes is crucial for their practical applications. Here, we show that quantum-dot light-emitting diodes may exhibit an anomalous degradation pattern characterized by a continuous increase in electroluminescent efficiency upon electrical stressing, which deviates from the typical decrease in electroluminescent efficiency observed in other light-emitting diodes. Various in-situ/operando characterizations were performed to investigate the evolutions of charge dynamics during the efficiency elevation, and the alterations in electric potential landscapes in the active devices. Furthermore, we carried out selective peel-off-and-rebuild experiments and depth-profiling analyses to pinpoint the critical degradation site and reveal the underlying microscopic mechanism. The results indicate that the operation-induced efficiency increase results from the degradation of electron-injection capability at the electron-transport layer/cathode interface, which in turn leads to gradually improved charge balance. Our work provides new insights into the degradation of red quantum-dot light-emitting diodes and has far-reaching implications for the design of charge-injection interfaces in solution-processed light-emitting diodes.
Inorganic–organic hybrid perovskites have drawn considerable attention in photovoltaics and light-emitting diodes (LEDs) due to their exceptional optoelectronic properties. Perovskite multiple ...quantum wells (MQWs), which employ large organic ammonium cations to form layered structures, have been developed for high-efficiency perovksite LEDs (PeLEDs). However, little is known about the impacts of large organic ammonium cations on the properties of MQW films. In this work, we report MQW perovskites of phenylbutylammonium-cesium lead iodides, which exhibit a photoluminescence peak at 664 nm with a quantum efficiency of 58%. These perovskite MQW films enable red LEDs with high external quantum efficiencies (EQEs) of up to 13.3%. Furthermore, we deposit MQW perovskites of butylammonium-cesium lead iodides. The comparisons of the two perovskite MQW films demonstrate that the choices of large organic ammonium cations significantly influence the properties of the perovskite MQW films, that is, distributions of the quantum-well thicknesses, energy transfer processes, and recombination channels of the emissive centers. Our study shall shed light on the rational design of high-performance perovskite MQW films toward their potential application as red light sources.
Solution‐processed, self‐organized multiple quantum well (MQW) perovskites possess good film coverage and high photoluminescence quantum efficiency, which are promising for high performance ...light‐emitting diodes (LEDs). However, due to the inclusion of insulating large organic cation as barrier layer, the charge transport in MQW perovskites is not as efficient as 3D perovskites, which limits the improvement of power conversion efficiency of MQW perovskite LEDs. Here, it is demonstrated that by molecular engineering, the conductivity of MQW perovskite film can be effectively increased by reducing the barrier width in QWs, thus leading to enhanced device performance. By controlling the constitution of the narrow‐barrier‐width MQW perovskites, one can achieve green LEDs with a high luminance of 30 000 cd m−2 at a low voltage of 6 V and a peak external quantum efficiency of 7.7%. Moreover, the green perovskite LEDs show a lifetime of 63 min with initial luminance of 1330 cd m−2, representing one of the best performing green perovskite LEDs. Here, a promising strategy is provided to further boost the efficiency, brightness, and stability of MQW perovskite LEDs.
The barrier width of multiple quantum well (MQW) perovskite is controlled through molecular engineering of the large organic cation. MQW perovskite films based on a novel benzimidazolium exhibit reduced barrier width and enhanced conductivity, leading to green perovskite light‐emitting diodes with high luminance and good stability.
Bulk-heterojunction (BHJ) organic solar cell (OSC) has become a major thrust in solar energy research. It is highly critical to fabricate large-area high-efficiency OSCs in order to maximize the ...fraction of active area and hence their practical application. In this paper, we have fabricated a promising hybrid transparent electrode consisting of high resolution embedded silver grid (Ag-grid) in hybridization with high conductance poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (PH1000), which gives both high transparency and low sheet resistance. We further demonstrate its application in large-area high efficiency OSCs. By carefully tuning the properties of the Ag-grid based hybrid electrodes, the sheet resistance is further reduced to as low as 1.2Ωsq−1. Inverted OSCs with device area of 1.21cm2 exhibited a record PCE of 3.36% for poly(3-hexylthiophene):6,6-phenyl-C61 butyric acid methyl ester (P3HT:PC61BM) blend film as the active layer; and the PCE of PTB7:PC71BM devices reached 5.85%. To the best of our knowledge, the PCE of 5.85% is the highest in large-area flexible OSCs (>1cm2) till date.
Large-area high-efficiency OSCs are prepared using Ag-grid based hybrid electrodes. Inverted OSCs with device area of 1.21cm2 exhibit a record PCE of 5.85%. Investigation on device area scaling behavior reveals that device morphology and electrode sheet resistance are two most important factors limiting the PCE for large-area OSCs. Ag-grid electrodes with ultra-low resistance are thus uniquely advantageous in turning lab-scale breakthroughs into practical large-scale devices. Display omitted
•High transparency and ultra-low sheet resistance hybrid electrodes were fabricated.•The hybrid electrode consisted of embedded Ag-grid and PH1000.•Ag-grid based hybrid electrode was used to fabricate inverted large area OSC.•We obtained a 5.85% PCE for OSC with device area 1.21cm2.•The relationship between device area and performance was proved by experiment and simulation.
Colloidal quantum dots（QDs）are a unique class of emissive materials with size-tunable emission wavelengths,saturated emission colors,near-unity luminance efficiency,inherent photo-and ...thermal-stability,and excellent solution processability.Display based on quantum-dot light-emitting diodes（QLED）may combine the superior properties of QDs,the benefits of solution-based fabrication techniques,and the advantages of self-emission devices,which promises an unprecedented generation of cost-effective,large-area,energysaving,wide-color-gamut,ultra-thin and flexible displays.
We demonstrate a facile and general strategy based on ligand protection for the synthesis of unstable colloidal nanocrystals by using the synthesis of pure p-type NiO nanocrystals as an example. We ...find that the introduction of lithium stearate, which is stable in the reaction system and capable of binding to the surface of NiO oxide nanocrystals, can effectively suppress the reactivity of NiO nanocrystals and thus prevent their in situ reduction into Ni. The resulting p-type NiO nanocrystals, a highly demanded hole-transporting and electron-blocking material, are applied to the fabrication of organic solar cells and polymer light-emitting diodes, demonstrating their great potential as an interfacial layer for low-cost and large-area, solution-processed optoelectronic devices.
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