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Upconversion devices (UCDs) have motivated tremendous research interest with their excellent potential and promising application in photovoltaic sensors, semiconductor wafer detection, biomedicine, and light conversion devices, especially near-infrared-(NIR)-to-visible upconversion devices. In this research, a UCD that directly turned NIR light located at 1050 nm into visible light located at 530 nm was fabricated to investigate the underlying working mechanism of UCDs. The simulation and experimental results of this research proved the existence of the quantum tunneling phenomenon in UCDs and found that the quantum tunneling effect can be enhanced by a localized surface plasmon.

Quantum dots (QDs) light-emitting diodes (QLEDs) are considered the most promising candidate for application in displays. While the efficiency of QLEDs has been greatly developed in recent years and is comparable to that of organic light-emitting diodes (OLEDs), it still remains challenging to realize both high efficiency and long lifetimes. In this work, we report efficient and stable red QLEDs with the maximum current efficiency of 13.48 cd A-1, external quantum efficiency of 18.65%, and low efficiency roll-off at high luminance with a long lifetime exceeding ∼2.9 × 105 h, representing a 3-fold increase in stability. Tailoring the composition of QDs suppresses nonradiative Forster resonant energy transfer and Auger recombination and provides favorable valence band alignment to boost the hole injection. Our work suggests that tailoring the nanostructures of QDs offers an effective means to simultaneously achieve high efficiency and high stability, accelerating QLED technology for practical applications in displays and lighting.

The optical properties of nonpolar AlGaN multiple quantum wells (MQWs) emitting at 280 nm were investigated intensively using temperature-dependent and time-resolved photoluminescence spectra associated with the characterization of structural properties. The densities of superficial pits and basal-plane stacking faults (BSFs) were reduced by 33.8% and 35.9%, respectively, for nonpolar AlGaN MQWs due to the carefully optimized dual nitridation. It was found that the nonpolar MQWs emission can be significantly improved by reducing the BSFs density as the BSFs emission was the main competing channels. Moreover, an internal quantum efficiency of 39% for nonpolar Al0.43Ga0.57N MQWs at emission wavelength of 279 nm was achieved even the full width at half maximum values of X-ray rocking curves were 0.565° for c-direction and 0.797° for m-direction. This fact means that a highly efficient deep ultraviolet light sources can be expected by means of nonpolar AlGaN due to the elimination of quantum confined Stark effect induced the decrease in radiative lifetime.

All inorganic perovskite quantum dots (QDs) have attracted much attention in optoelectronic devices due to their fascinating properties such as high photoluminescence quantum yields (PLQYs), narrow emission peaks, and facile synthesis processes. Herein, we report a synergistic strategy of interfacial engineering and passivation. We construct an inverted device structure with zinc magnesium oxide (Zn0.95Mg0.05O) as an electron transport layer and the p–n charge generation junction of (N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine/1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile) as a hole transport layer to facilitate and balance the charge injection/transport. Meanwhile, a facile post-passivation technique is employed to passivate cesium lead bromide (CsPbBr3) QDs via supplementing Br anions. The treated QDs exhibit improved PLQY due to decreased surface defect sites and enhanced radiative recombination. As a result, our perovskite quantum dot light-emitting diodes (PVQDLEDs) achieve a maximum luminance of 75 792 cd m−2, an extremely low turn-on voltage of 1.9 V, and a maximum external quantum efficiency (EQE) of 5.95%, leading to an increase in EQE by 100% compared with those of the control device. Our work offers an effective approach to improve the performance of PVQDLEDs via multiple effects for their application in displays and solid-state lighting.

All-inorganic quantum dot light-emitting diodes (QLEDs) show promise for advanced lighting and display due to their superior advantage in stability. However, all-inorganic QLEDs suffer from low efficiency because of the exciton quenching and inefficient hole transport from the inorganic hole transport layer (HTL) to QDs. Herein, we demonstrate an efficient all-inorganic QLED with NiO nanoparticles (NPs) HTL modified by 11-mercaptoundecanoic acid (MUA). The MUA can passivate the defects of NiO and suppress the exciton quenching. Moreover, the declined valence band level of modified NiO could facilitate the hole transport, promoting the charge balance. In addition, the surface engineering improves the quality of the NiO film, leading to the decrease of current leakage. As a result, the maximum current efficiency and external quantum efficiency (EQE) of our QLEDs achieve 5.50 cd/A and 1.28%, respectively, exhibiting an enhancement of 4.5- and 1.72-fold, respectively. Meanwhile, the stability of the device is...

Herein, a highly-efficient quantum dot light-emitting diode (QLED) with stacked blue and yellow quantum dot (QD) layers can be demonstrated to output white light. A buffer layer of ZnO nanoparticles (NPs) inserted between two QD layers can prevent them from mixing and penetrating. In order to promote charge balance, Zn0.95Mg0.05O was employed as the electron transport layer (ETL), which can block excessive electrons due to the 0.07 eV higher conduction band minimum (CBM) level compared to that of pristine ZnO, leading to the suppression of exciton quenching. In addition, the lower defect concentration and lowered conductivity of Zn0.95Mg0.05O due to the reduction of oxygen vacancies by doping the Mg element into ZnO can also benefit the inhibition of exciton quenching. The device can be demonstrated with a maximum luminance current efficiency of 24.6 cd A−1 and power efficiency of 25.8 lm W−1, exhibiting a 19% and 38% enhancement, respectively. The strategy demonstrated here demonstrates a promising way to realize highly efficient white QLEDs and also other optoelectronic devices.

In this paper, It is fully demonstrated that the characteristics of the vertical cavity surface emitting laser (VCSEL) can be versatilely engineered by independent adjustment of the cavity and solution-processable CdSe/ZnS quantum dots (QDs), featuring low threshold (8.9 µJ/cm2), directional output (beam divergence of ≈ 10 degree), and favorable stability. Importantly, the lasing wavelength can be broadcasted to cover across the red, green, and blue region maintaining comparable thresholds, which is promising in developing single-source-pumped full-color visible lasers. The results unambiguously reveal the feasibility of CdSe/ZnS QDs as practical laser media.

A high-performance solution processed quantum dot light emitting diode (QLED) has been fabricated via modulating the hole transport by doping 1-bis[4-[N,N-di(4-tolyl)amino]phenyl]-cyclohexane (TAPC) into poly-N-vinylcarbazole (PVK) as the hole transport layer (HTL). With a low doping content, the hole transport ability of the HTL can be enhanced due to the extremely high hole mobility of TAPC. However, increasing the doping ratio of TAPC excessively results in degraded performance of the QLED due to the deteriorated film quality and increased energy barrier from the HTL to the quantum dots (QDs), which is attributed to the relatively shallow position of the HOMO level for TAPC. Using the optimized composition ratio of the doped HTL (3 : 1 vol% of PVK : TAPC), the best QLED performance was achieved with a low turn-on voltage of 3.3 V due to the charge balance, which facilitates exciton recombination in the emissive layer (EML). In addition, the highest current efficiency (26.2 cd A−1), power efficiency (19.2 lm W−1), external quantum efficiency (6.2%) and 60% enhancement in the stability of the device were achieved. The improvement in the device performance can be attributed to the suppression of Auger recombination due to the balance of carrier injection into the emissive layer composed of QDs and the separation of the carrier accumulation zone from the exciton formation interface by the modulation of hole transport. The lowered turn-on voltage and improved efficiency presented here offer potential for high throughput and practical use for commercialized QLED displays.

The quantum dot light-emitting diode (QLED) is a promising candidate for the display and lighting applications. The fabrication of such devices by solution processing allows considerable cost reduction and is therefore very attractive for industrial manufacturers. In this paper, we report on the all solution-processed inverted QLEDs by incorporating with the solvent modified PEDOT:PSS. The effect of isopropanol (IPA) doping concentration in the PEDOT:PSS hole injection layer (HIL) on device performance was investigated, with the aim of facilitating the surface hydrophilicity and hole transport rate between HIL and hole transfer layer. It is demonstrated that the optimal amount of IPA doped in the HIL can significantly improve the performance of QLEDs in this study.

We report an inverted and multilayer quantum dot light emitting diode (QLED) which boosts high efficiency by tuning the energy band alignment between charge transport and light emitting layers. The electron transport layer (ETL) was ZnO nanoparticles (NPs) with an optimized doping concentration of cesium azide (CsN3) to effectively reduce electron flow and balance charge injection. This is by virtue of a 0.27 eV upshift of the ETL's conduction band edge, which inhibits the quenching of excitons and preserves the superior emissive properties of the quantum dots due to the insulating characteristics of CsN3. The demonstrated QLED exhibits a peak current efficiency, power efficiency and external quantum efficiency of up to 13.5 cd A-1, 10.6 lm W-1 and 13.4% for the red QLED, and correspondingly 43.1 cd A-1, 33.6 lm W-1 and 9.1% for green, and 4.1 cd A-1, 2.0 lm W-1 and 6.6% for the blue counterparts. Compared with QLEDs without optimization, the performance of these modified devices shows drastic improvement by 95.6%, 39.4% and 36.7%, respectively. This novel device architecture with heterogeneous energy levels reported here offers a new design strategy for next-generation high efficiency QLED displays and solid-state lighting technologies.

The first aqueous red CdTe QD-LED was fabricated with the structure of ITO/PEDOT:PSS/PVK/CdTe QDs/ZnO/Al. The device has been considered to be an advanced aqueous QD-LED, which demonstrated a turn-on voltage of about 5 V. Further, its current density and brightness would also reach 92 mA cm−2 and 58 cd m−2 at the voltage of 10 V. Moreover, we found that there were two essential factors for fabricating an aqueous QD-LED successfully: (1) adding wet agent to the QD solution, (2) removing the composite ions remaining in the QD solution. Meanwhile, the EL intensity of the aqueous QD-LEDs will perform better if the solution of QDs is acidic. These results offer a promising approach to the further development of aqueous QD-LEDs.

We report a color-saturated, red quantum dot light-emitting diode (QD-LED) using graphene oxide doped PEDOT:PSS (PEDOT-GO) as the hole injection layer (HTL) to optimize the band offset between the HTL and emitting layers. As the doping concentration of the GO increases, the valence band of the PEDOT-GO down-shifts by 0.66 eV approaching that of the QDs. Meanwhile, the conductivity and transparency linearly changes as the doping concentration of GO increases. The QD-LEDs show a maximum luminance of up to 4200 cd/m2, corresponding to 7.5 lm/W in power efficiency and a turn-on voltage of 1.6 V. It is worth noting that the reduced turn-on voltage can be attributed to the direct exciton recombination within the QDs. Overall, there is a sixfold enhancement in the performance of the QD-LED with graphene oxide due to the higher hole injection/transfer rate and lower operating voltage.

Colloidal quantum dots (QDs) with a ZnO core were synthesized with subsequent surface passivation by MgO. The photo-enhancement effect of the near band-edge photoluminescence (PL) in ZnO nanocrystals, dispersed in ethanol, is investigated by observing changes in the optical properties after ultraviolet (UV) exposure. Finally, the operation as a light-emitting device (LED) was demonstrated experimentally for these ZnO-based quantum dots (QDs). The results indicate that this type of QDs might enable the development of electroluminescent UV sources in the near future.

Flexible quantum dot light emitting diodes (QLEDs) have attracted extensive attention owing to the advantages of foldability and their broad application in flexible display devices. In this work, we report high performance, mechanically flexible QLEDs based on ZnO nanoparticles used as an electron transfer layer (ETL). The QLEDs have been fabricated on poly(ethylene-terephthalate) (PET) substrates utilizing a unique structure consisting of bilayered hole transport films and ZnO nanoparticles acting as an ETL to improve the device performance owing to its appropriate energy band position and high charge mobility. The QLEDs exhibited high performance, such as a lowered turn on voltage of 1.6 V and improved current and power efficiencies of 5.20 cd A−1 and 1.80 lm W−1, respectively. They presented good flexibility with a critical bending radius of 4.5 mm, suggesting the broad application potential of flexible QLEDs.

The structural and optical properties for a nonpolar GaN epilayer grown with an in situ SiN x interlayer was studied intensively. The superficial defects were decreased by 83% and root-mean-square was reduced by 61% for nonpolar GaN with an SiN x interlayer. The in situ SiN x was revealed to be powerful to block basal-plane stacking faults (BSFs) in nonpolar GaN because BSF density was reduced from 1.83 × 105 to 8.13 × 104 cm−1 and BSF-related emission was remarkably suppressed by the SiN x interlayer. Moreover, the fast decay lifetime increased from 16.2 to 71.1 ps, which implied the non-radiative recombination in nonpolar GaN was significantly suppressed after the insertion of the SiN x layer.

In this paper, we have fabricated quantum dot light-emitting diode (QD-LED) based on silver (Ag) electrode. The QD-LED with Ag electrode is demonstrated with decreased leakage current, improved luminous efficiency, low turn-on voltages, and saturated emission exhibiting the Commission Internationale de l’Enclairage coordinates of (0.59, 0.40). Meanwhile, compared to the QD-LED with indium tin oxide-coated polyethylene terephthalate electrode, the electroluminescence intensity was enhanced twice for QD-LED based on Ag electrode, and turn-on voltage was reduced to 4.7 V, which was attributed to the higher conductivity and better transmission of Ag electrode.

We have fabricated all-inorganic quantum-dot light-emitting devices(QDLED) with NiO as a hole transporting layer and TiO2 as a inorganic electron transporting layer. P-type NiO and n-type TiO2 charge-transport layers were synthesized by sol-gel method using spin-coating technique. The thickness of TiO2 layer was optimized with different spin-coating speed, and studied the luminescence characteristics of devices. Results indicated devices with 4000 rpm TiO2 layer has lower turn voltage 4.2V and higher EL intensity.

The large area quantum dots light diode assays were fabricated by using CdSe/ZnS core/shell quantum dots (QDs) as light emitting layer, ZnO nanoparticles (NPs) as an electron transport/injection layer (ETL) and organic polymers as hole transport layer (HTL). The performance of the device was measured for samples of different thicknesses of QDs layer. By optimizing the constituent layers thicknesses, light emitting diode arrays (10 cm×10 cm active area, 32×32 pixel) were fabricated with improved electroluminance efficiency (1 to 1.8 Cd/A), low turn-on voltages (3.2 V) and pure QDs emission. These findings suggest that such simple tuning techniques in these LEDs will be promising for use in practical flat panel displays (FPDs).

The coupling of localized surface plasmon resonance (LSPR) and excitons in nanomaterials can improve the performance of nano-optoelectronic devices. We synthesized a quantum dot (QD) capped gold (Au) nanoparticle (NP) composite to use as an emitting layer in all-inorganic quantum dot light-emitting diodes (QD-LEDs). The photoluminescence (PL) peak of the QDs is fully overlapped with the absorption peak of the Au NPs to realize the maximum LSPR enhancement. The LSPR effect of the QD-capped Au NPs has been demonstrated by increased radiative emission, PL excitation intensity, and reduced exciton lifetime evidenced by time-resolved PL measurement. As a result, a quantum yield of 60% for the QD-capped Au NPs has been realized and the QD-LED has achieved a remarkably enhanced power efficiency of 6.2 lm W−1 and maximum brightness of 1005 cd m−2 under various optimization conditions. These results demonstrate that QD-capped Au NPs constitute an effective route for achieving high-performance optoelectronic devices.

Here, we report on the hybrid hole transport materials 4,4'-bis-(carbazole-9-yl)biphenyl (CBP) or poly-N-vinylcarbazole (PVK) doped into poly(4-butyl-phenyl-diphenyl-amine) (Poly-TPD) as the hybrid hole transport layer (HTL) to tailor the energy band alignment between hole injection layer (HIL) and quantum dot (QD) light emitting layer in order to realize efficient quantum dot light emitting diodes (QLEDs) in all solution-processed fabrication. Compared to the pristine Poly-TPD based device, it is found that the electroluminescence (EL) performance of QLEDs can be significantly improved by 1.5 fold via addition of CBP into Poly-TPD, which can be attributed to the lowered highest occupied molecular orbital (HOMO) level of Poly-TPD to reduce the energy barrier between HTL and valance band (VB) of QDs. Thus, after doping small molecules into polymer under optimized proportion (Poly-TPD:CBP = 2:1 by weight), the hole transport rate can be balanced, facilitating the carrier injection from HTL to QDs and enhancing the efficiency of QLEDs. As a result, a maximum luminance, a maximum current efficiency and a maximum power efficiency of 7600 cd/m2, 5.41 cd/A and 4.25 lm/W can be obtained based on this variety of hybrid HTL employed QLEDs.

White quantum dot light-emitting diodes (QD-LEDs) have been a promising candidate for high-efficiency and color-saturated displays. Here, we report a simply solution-processed white QD-LED using ZnO QDs as emitters. The device is demonstrated with a maximum luminance of 300 cd/m2, exhibiting the Commission Internationale de l’Enclairage coordinates of (0.33, 0.33). The unencapsulated white QD-LED has a long lifetime of 120 h. These results indicate that ZnO QDs provides an alternate and effective approach to achieve high-performance white QD-LEDs and also other optoelectronic devices.

Surface plasmon-enhanced electroluminescence (EL) has been demonstrated by incorporating gold (Au) nanoparticles (NPs) in quantum dot light-emitting diode (QLED). Time-resolved photoluminescence (TRPL) spectroscopy reveals that the EL enhancement is ascribed to the near-field enhancement through an effective coupling between excitons of the quantum dot emitters and localized surface plasmons around Au NPs. It is found that the size of Au NPs and the distance between the Au NPs and the emissive layer have significant effects on the performance of QLED. The enhancement can be maximized as the SP resonance wavelength of Au NPs matches well with the PL emission wavelength of the QD film and the distance between Au NPs and the emissive layer maintains 15 nm. The photoluminance (PL) and EL intensity can be enhanced by 4.4 and 1.7 folds with the incorporation of Au NPs. The maximum current efficiency of 4.56 cd/A can be achieved for the resulting QLEDs by incorprating Au NPs with an enhancement factor of 2.0. In addition, the enhancement ratio of 2.2 can be achieved for the lifetime of resulting QLED.

In this paper, a photo-modulated transistor based on the thin-film transistor structure was fabricated on the flexible substrate by spin-coating and magnetron sputtering. A novel hybrid material that composed of CdSe quantum dots and reduced graphene oxide (RGO) fragment-decorated ZnO nanowires was synthesized to overcome the narrow optical sensitive waveband and enhance the photo-responsivity. Due to the enrichment of the interface and heterostructure by RGO fragments being utilized, the photo-responsivity of the transistor was improved to 2000 A W−1 and the photo-sensitive wavelength was extended from ultraviolet to visible. In addition, a positive back-gate voltage was employed to reduce the Schottky barrier width of RGO fragments and ZnO nanowires. As a result, the amount of carriers was increased by 10 folds via the modulation of back-gate voltage. With these inherent properties, such as integrated circuit capability and wide optical sensitive waveband, the transistor will manifest great potential in the future applications in photodetectors.