Quantum Dot Heterojunction Research Articles

Hydrothermal synthesis of Se-doped MoS2 quantum dots heterojunction for highly efficient photocatalytic degradation

In this work, we were demonstrated that the synthesis and photocatalytic performance of MoSSe quantum dots (QDs) for degradation of organic pollutants. Congo red (CR) solution was taken as the target compound to check the photocatalysis. As intended, the MoSSe QDs observe enhanced photocatalytic activity approximately 5.26–6.25 times higher compared to bulk components after 60 min under visible light. In addition, the radical-trapping tests and electron spin resonance also demonstrate that superoxide radicals and photo-induced holes are primary reactive species for photodegradation. MoSSe QDs exhibited great photodegradation of CR under simulated sunlight, which mostly refer to the quantum confinement effect from high specific surface area and excellent separation of the photo-induced electron and hole pairs.

Nanocomposite Photoanodes Consisting of p-NiO/n-ZnO Heterojunction and Carbon Quantum Dot Additive for Dye-Sensitized Solar Cells

To increase the performance of power conversion efficiency of dye-sensitized solar cells (DSSCs), in the current paper, nanocomposites of n-type ZnO and p-type NiO semiconductors were constructed a...

Research progress in the epitaxial growth of silicon-based group IV materials, and their light emitters and photodetectors

Silicon-based optoelectronic integrated circuits, which are composed of silicon-based light sources, photodetectors, light modulators, and other modules, are core technologies in the recent information era. Silicon is the cornerstone of microelectronic integration, but it encounters issues with optoelectronic integration. First, as an indirect bandgap material, silicon is difficult to be used in high-efficiency light sources, which is still currently the biggest challenge. Second, the absorption coefficient of silicon in the near-infrared communication band is very low, so it is not suitable for the near-infrared photodetectors. Silicon-compatible group IV materials can achieve direct band through band engineering. They have a high absorption coefficient in the near-infrared and have attracted extensive attention of researchers. In this paper, the research progress of epitaxial growth of silicon-based materials, and their light emitters and photodetectors, are reviewed. The growth technologies of Ge, SiGe/Ge heterojunction, quantum wells, and GeSn quantum dots are introduced. Based on the above silicon-based group IV heterostructure materials, a new method for modulating the height of the contact barrier between metal and semiconductor was proposed. Also, various photodetectors with different structures were developed. The lateral heterojunction LED and vertical resonant-cavity LED, including dual active regions compatible with traditional CMOS processes, were developed. The luminescence performance of the devices was improved effectively and the luminescence gain of strain Ge was observed.

A metal-organic framework-derived Zn1-xCdxS/CdS heterojunction for efficient visible light-driven photocatalytic hydrogen production.

ZCS-C (ZnCdS/CdS) QDs were synthesized via low-temperature vulcanization using zeolitic imidazolate framework-8 (ZIF-8) nanoparticles as a precursor, cation exchange, and heterojunction construction. Without any precious metal as a cocatalyst, the photocatalytic hydrogen production rate of ZCS-C-3 QDs reached 2.7 mmol g-1 h-1 under visible light irradiation. The optimized sample exhibited an outstanding chemical stability and recyclability, which is superior to most of the reported Zn1-xCdxS-based photocatalysts.

Synthesis of Z-scheme cobalt porphyrin/nitrogen-doped graphene quantum dot heterojunctions for efficient molecule-based photocatalytic oxygen evolution

CoP nanowires are transformed to 0D Z-scheme CoP/NGQDs heterojunctions in the present of NGQDs, which exhibit the currently highest POE rate on the molecule (350 μmol g−1 h−1) due to the generation of a new excited state of (CoP+·NGQDs−)*.

Vertically Stacked Intraband Quantum Dot Devices for Mid-Wavelength Infrared Photodetection.

Intraband quantum dots are degenerately doped semiconductor nanomaterials that exhibit unique optical properties in mid- to long-wavelength infrared. To date, these quantum dots have been only studied as lateral photoconductive devices, while transitioning toward a vertically stacked structure can open diverse opportunities for investigating advanced device designs. Here, we report the first vertical intraband quantum dot heterojunction devices composed of Ag2Se/PbS/Ag2Se quantum dot stacks that bring the advantage of reduced dark conductivity with a simplified device fabrication procedure. We discuss the improvement in the colloidal synthesis of Ag2Se quantum dots that are critical for vertical device fabrication, identify an important process that determines the mid-wavelength infrared responsivity of the quantum dot film, and analyze the basic device characteristics and key detector performance parameters. Compared to the previous generation of Ag2Se quantum dot-based photoconductive devices, approximately 70 times increase in the mid-wavelength responsivity, at room temperature, is observed.

Study on the performance of ZMO/PbS quantum dot heterojunction solar cells

In this work, the Mg-doped ZnO (ZMO)/Lead sulfide (PbS) quantum dot (QD) heterojunction solar cells are fabricated via layer-by-layer spin-coating method. The quantum dot solar cells (QDSCs) with structure of FTO/ZMO/PbS-EMII/PbS-EDT/Au and relatively larger area of 0.372 cm2 are prepared in ambient atmosphere. The effect of PbS active layer thickness on the photovoltaic performance of PbS QDSCs is investigated under room temperature of 293 K. It is concluded that seven spin-coating cycles of PbS active layers is the best choice for the device, and the cell with that achieves a power conversion efficiency (PCE) of 9.46%. Furthermore, the temperature dependent characteristics of PbS QDSCs are studied. It is exhibited that the power efficiency improves as the device temperature increases first then shows a decreasing trend as the temperature substantially rises. As a result, a highest PCE of 12% is shown at the working temperature of 273 K due to higher VOC and FF. Moreover, it is demonstrated the PbS QDSCs possess noticeably stability for over 30 days of storage in air.

All-solution-processed, highly efficient and stable green light-emitting devices based on Zn-doped CsPbBr3/ZnS heterojunction quantum dots

The low-cost, solution-processed and stable perovskite quantum dots (QDs) light-emitting diodes (QLEDs) have great potential applications for the new-generation displays technology and white-LEDs. The stability of perovskite QDs has been improved via polymers or inorganic encapsulation strategies, but at the cost of their semiconducting properties, so it is not suitable for active light-emitting devices. In this paper, the Zn-doped CsPbBr3/ZnS QDs heterojunction were fabricated via a simple solution-phase method, which demonstrated simultaneously enhanced the optical properties and stability of perovskite QDs films without damaging their semiconducting properties. The photoluminescence quantum yields and stability of the Zn-doped CsPbBr3/ZnS heterojunction QDs films have been significantly improved because of good surface passivation on the surface defects of perovskite QDs with ZnS nanoclusters and Zn2+ doping. Finally, solution-processed n-ZnO nanoparticles (NPs) and p-NiO NPs as carrier transport layers are used to fabricate all-inorganic Zn-doped CsPbBr3/ZnS QLEDs. The QLEDs show high-efficiency green light emission with a maximum luminance of 8600 cd/m2 and external quantum efficiency of 4.8%. Moreover, the researched green perovskite QLEDs also show good working stability after a long test time in the outside environment. This study may provide an effective way for the preparation high-performance perovskite QLEDs with good environmental stability, making practical applications possible.

Enhanced photoluminescence of a CsPbBr3/Al2O3 film heterojunction enabled by coupling of gold nanoparticles

We studied an enhanced photoluminescence (PL) effect of CsPbBr3/Al2O3 heterojunction by using gold nanoparticls (NPs). The CsPbBr3/Al2O3 heterojunction and CsPbBr3/Au/Al2O3 heterojunction were respectively prepared on porous Al2O3 film by using a colloidal self-assembly method. The defect fluorescence of CsPbBr3/Al2O3 heterojunction was enhanced up to 40 times due to the transfer of photo-generated carriers from the CsPbBr3 quantum dots (QDs) to the porous Al2O3 film. To suppress the defect fluorescence of heterojunction, the CsPbBr3/Au/Al2O3 heterojunction was prepared by loading the gold NPs between the CsPbBr3 QDs film and the porous Al2O3 film. The results showed that the gold NPs facilitated the transfer of the photo-generated carriers from the CsPbBr3 QDs to the surface of porous Al2O3 film. Compared with the porous Al2O3 film and CsPbBr3/Al2O3 heterojunction, the peak fluorescence of CsPbBr3/Au/Al2O3 heterojunction was enhanced to 6.4 times and 2.8 times, respectively. This method of enhanced fluorescence of QD heterojunction provides a new pathway in the applications of photovoltaic, photodetector, LED, image sensor, photocatalysis.

Performance enhancement of heterojunction ZnO/PbS quantum dot solar cells by interface engineering

Effective charge transport through heterojunction interface in Quantum dots (QDs) based solar cells is difficult due to the spherical structure of QDs. Therefore tuning of QDs size for uniform and defect free heterojunction interface becomes very important to get optimum device performance. Here we have optimized the performance of ZnO Nanocrystals (NCs)/lead sulfide (PbS) QDs heterojunction solar cell by controlling the surface roughness of ZnO NCs thin films. The synthesized ZnO NCs aggregation was tuned by varying the binary solvent volume ratio of chloroform and methanol (CF:MeOH), which leads to the different surface roughness. The thin film of ZnO NCs having surface roughness comparable to the size of PbS QDs performs better as compared to those devices having different surface roughness. The optimum device fabricated in an ambient atmosphere with ZnO NCs thin film having surface roughness 4.36 nm, and nanocrystal size 3.32 nm as synthesized with (CF:MeOH) volume ratio of (2:1), shows the highest efficiency of 2.94% among other devices in the same structure due to decreased leakage current and improved junction interface contact between active materials. This work reveals that the controllability of ZnO NCs surface roughness and its correlation with the size of QDs can contribute to further improvement of low cost QDs based solar cells.

Annealing-Temperature Dependent Carrier-Transportation in ZnO/PbS Quantum Dot Solar Cells Fabricated Using Liquid-Phase Ligand Exchange Methods

We constructed ZnO/PbS quantum dot (QD) heterojunction solar cells using liquid-phase ligand exchange methods. Colloidal QD solutions deposited on ZnO-dense layers were treated at different temperatures to systematically study how thermal annealing temperature affected carrier transport properties. The surface of the layers became dense and smooth as the temperature approached approximately 80 °C. The morphology of layers became rough for higher temperatures, causing large grain-forming PbS QD aggregation. The number of defect states in the layers indicated a valley-shaped profile with a minimum of 80 °C. This temperature dependence was closely related to the amount of residual n-butylamine complexes in the PbS QD layers and the active layer morphology. The resulting carrier diffusion length obtained on the active layers treated at 80 °C reached approximately 430 nm. The solar cells with a 430-nm-thick active layer produced a power conversion efficiency (PCE) of 11.3%. An even higher PCE is expected in solar cells fabricated under optimal annealing conditions.

Design modern structure for heterojunction quantum dot solar cells

This paper proposal new structure for improving the optical, electrical characteristics and efficiency of 3rd generation heterojunction quantum dot solar cell (HJQDSC) (ITO/CdS/QDPbS/Au) model by using the quantum dot window layer instead of bulk structure layers cell. Also, this paper presents theoretically analysis for the performance of the proposal HJQDSC (ITO/QDCdS/QDPbS/Au) structure. The new design structure was applied on traditional (SnO2/CdS/CdTe/Cu) and (ZnO/CdS/CIGS/Mo) thin film solar cells which based on sub-micro absorber layer thickness models by replacing the bulk CdTe, CIGS absorber layers and CdS window layer with quantum dot size materials to achieve higher efficiency with lesser usage layer material. Also, it has been studied the effect of using semiconductors layers in quantum dots size on electric and optical properties of thin film solar cells and the effect of window and absorber layers quantum dots radii on the performance of solar cells. Finally, a thermal efficiency analysis has been investigated for explaining the importance of new structure HJQD solar cells.

MOF-Templated Metal Oxides Sensitized with Quantum Dots Heterojunction for Efficient Solar Fuels Generation

The separation and transport of photogenerated charges carriers are two of the most crucial factors that determine the overall efficiency of photoelectrochemical (PEC) systems. Various strategies have been exploited for achieving efficient charge separation and transfer. Among them, the design of semiconductor heterojunction has been shown to be one of the most effective approaches. Metal oxides, such as TiO2, are the among the most common materials for water splitting. However, the control of phase alignment and the interface structure remains a challenge. A promising solution is to use a template approach by employing metal-organic frameworks (MOF) which are of broad interest as a new class of organic-inorganic hybrid materials and have been intensely exploited in various fields due to their unique physical and chemical properties. Furthermore, common metal oxides, such TiO2 or NiO have limited absorption of sunlight due to their large intrinsic band gap (i.e. TiO2 anatase: 3.2 eV) which hinders effective use in solar water splitting. To extend the absorption range of the MOF-templated metal oxides in the visible and near-infrared range, we employed metal chalcogenide QDs as sensitizers.In this presentation, for example, we explore a simple metal organic framework (MOF)-derived synthesis to obtain a controlled mixed-phase (anatase and rutile) of TiO2 nanoparticles, which retain the MOF crystal morphology. After sensitization with core@shell CdSe@CdS QDs, the mixed-phase TiO2 film exhibited a remarkable photocurrent of 10.72 mA/cm2 and long-term stability, with a retained value of more than 78.1% after two hours. Compared with commercial TiO2 films, the MOF-derived TiO2 film sensitized by core-shell CdSe@CdS QDs, showed an enhanced PEC device stability of +42.1% and PEC performance of +47.6%. The enhanced performance is due to the presence of mixed rutile/anatase phases, that creates a favorable band energy alignment for the separation of the photogenerated charges. The proposed photoanode based on MOF-derived metal oxide is an efficient strategy to improve the efficiency of the heterojunction-based PEC system for hydrogen generation. Furthermore, the combined use of QDs can extend the absorption range exploiting a larger part of the sun spectrum. Figure 1

High performance CsPbBr3 quantum dots photodetectors by using zinc oxide nanorods arrays as an electron-transport layer

The electron transport layer (ETL) in perovskite photodetectors is playing a vital role in highly efficient electron extraction. Herein, this work reports a perovskite photodetector based on hydrothermal-fabricated ZnO nanorods (NRs) as the ETL and hot-injection-fabricated CsPbBr3 quantum dot (QD) as the photoabsorber. The crystalline structure, morphologies, and photoluminescence (PL) of the materials and the physics mechanism of highly efficient electron extraction in the devices are characterized and analyzed. The PL and time-resolved PL confirm the reduced recombination and enhanced electron transport to the indium tin oxide anode. The photodetectors based on ZnO NRs/CsPbBr3 QDs exhibit enormous enhancement in the response parameters such as a rise time of 12 ms, a decay time of 38 ms, and an on/off ratio of 3000, compared with the photodetectors based on ZnO films/CsPbBr3 QDs. These results indicate that the fabricated ZnO NRs/CsPbBr3 QDs heterojunction has a wide prospect of future applications in photodetectors.

Inverted Si:PbS Colloidal Quantum Dot Heterojunction-Based Infrared Photodetector.

Silicon and PbS colloidal quantum dot heterojunction photodetectors combine the advantages of the Si device and PbS CQDs, presenting a promising strategy for infrared light detecting. However, the construction of a high-quality CQDs:Si heterojunction remains a challenge. In this work, we introduce an inverted structure photodetector based on n-type Si and p-type PbS CQDs. Compared with the existing normal structure photodetector with p-type Si and n-type PbS CQDs, it has a lower energy band offset that provides more efficient charge extraction for the device. With the help of Si wafer surface passivation and the Si doping density optimization, the device delivers a high detectivity of 1.47 × 1011 Jones at 1540 nm without working bias, achieving the best performance in Si/PbS photodetectors in this region now. This work provides a new strategy to fabricate low-cost high-performance PbS CQDs photodetectors compatible with silicon arrays.

High quality silicon: Colloidal quantum dot heterojunction based infrared photodetector

The integration of silicon (Si) and nanomaterials with infrared light harvesting capability is a promising approach to fabricate large area infrared light detecting arrays. However, the construction of a high quality junction between Si and small bandgap colloidal quantum dots (CQDs) remains a challenge, which limited their photodetecting performance in the short wavelength infrared region (1.4 μm–3 μm). Herein, a layer of solution processed ZnO nanoparticles was inserted between silicon and CQDs to passivate the surface dangling bond of silicon. This significantly reduces the carrier recombination between Si and CQDs. Meanwhile, the formation of the Si:CQD heterojunction structure enables effective carrier extraction. As a result, the photodetector shows the detecting range to the short wavelength infrared region (0.8 eV) and achieves a standard detectivity of 4.08 × 1011 Jones at a bias of −0.25 V at room temperature.

Violet Light-Emitting Diodes Based on p-CuI Thin Film/n-MgZnO Quantum Dot Heterojunction.

As the lighting technology evolves, the need for violet light-emitting diodes (LEDs) is growing for high color rendering index lighting. The present technology for violet LEDs is based on the high-cost GaN materials and metal-organic chemical vapor deposition process; therefore, there have recently been intensive studies on developing low-cost alternative materials and processes. In this study, for the first time, we demonstrated violet LEDs based on low-cost materials and processes using a p-CuI thin film/n-MgZnO quantum dot (QD) heterojunction. The p-CuI thin film layer was prepared by an iodination process of Cu films, and the n-MgZnO layer was deposited by spin-coating presynthesized n-MgZnO QDs. To maximize the performance of the violet LED, an optimizing process was performed for each layer of p- and n-type materials. The optimized LED with 1 × 1 mm2-area pixel fabricated using the p-CuI thin film at the iodination temperature of 15 °C and the n-MgZnO QDs at the Mg alloying concentration of 2.7 at. % exhibited the strongest violet emissions at 6 V.

Plasmonic Effects of Dual-Metal Nanoparticle Layers for High-Performance Quantum Dot Solar Cells

To improve quantum dot solar cell performance, it is crucial to make efficient use of the available incident sunlight to ensure that the absorption is maximized. The ability of metal nanoparticles to concentrate incident sunlight via plasmon resonance can enhance the overall absorption of photovoltaic cells due to the strong confinement that results from near-field coupling or far-field scattering plasmonic effects. Therefore, to simultaneously and synergistically utilize both plasmonic effects, the placement of different plasmonic nanostructures at the appropriate locations in the device structure is also critical. Here, we introduce two different plasmonic nanoparticles, Au and Ag, to a colloidal PbS quantum dot heterojunction at the top and bottom interface of the electrodes for further improvement of the absorption in the visible and near-infrared spectral regions. The Ag nanoparticles exhibit strong scattering whereas the Au nanoparticles exhibit an intense optical effect in the wavelength region where the absorption of light of the PbS quantum dot is strongest. It is found that these dual-plasmon layers provide significantly improved short-circuit current and power conversion efficiency without any form of trade-off in terms of the fill factor and open-circuit voltage, which may result from the indirect contact between the plasmonic nanoparticles and colloidal quantum dot films.

Construction of a direct Z-scheme ZnS quantum dot (QD)-Fe2O3 QD heterojunction/reduced graphene oxide nanocomposite with enhanced photocatalytic activity

A novel direct Z-scheme ZnS quantum dot (QD)-Fe2O3 QD heterojunction/reduced graphene oxide (rGO) (GZxFy) nanocomposite was successfully synthesized by a simple hydrothermal method. The surface of ZnS and Fe2O3 QDs was modified by COOH and OH groups, respectively. ZnS QDs can be covalently bonded with Fe2O3 QDs by the dehydration reaction to form the ZnS QDs-Fe2O3 QDs heterojunctions. The GZxFy nanocomposites displayed the highest photodegradation efficiency of 96.45% (40 min, UV light) and 90.17% (480 min, visible light) for methylene blue when the mass ratio of ZnS QDs to Fe2O3 QDs was 1:3. The excellent photocatalytic activity could be attributed to the enhanced light-harvesting ability, high large specific surface area, efficient interfacial charge-carrier separation and transfer as well as the low charge transfer resistance. Ultraviolet photoelectron spectroscopy and radical trapping experiments were used to confirm the Z-scheme mechanism formed between ZnS QDs and Fe2O3 QDs, and verify the electron transfer direction for UV or visible light-driven photocatalytic reactions. GZ1F3 nanocomposites showed the excellent superparamagnetic behavior, which enabled its rapid magnetic recycle from the solution within 95 s in a magnetic field.

P-GaN/n-ZnO Nanorod/CsPbBr3 Quantum Dots Decorated with ZnO Nanoseeds for Light-Emitting Diodes

In this paper, we report the dual-wavelength green-light emission from zinc oxide (ZnO)-nanoseed-decorated p-GaN (gallium nitride)/n-ZnO nanorod/CsPbBr3 quantum dots (QDs) light-emitting diodes (LEDs). At the same time, the effect of ZnO nanoseeds on the p-GaN/n-ZnO nanorod/CsPbBr3 QDs LED performance is deeply studied. ZnO nanoseeds were fabricated by magnetron sputtering and the sol–gel method; then ZnO nanorods were obtained on GaN by hydrothermal treatment to form the p-GaN/n-ZnO nanorod heterojunction, and green CsPbBr3 QDs were further deposited on ZnO nanorod arrays to realize LEDs. The results show that magnetron-sputtering ZnO nanoseeds can induce regular vertical ZnO nanorod arrays, and the corresponding device presents a better electroluminescence (EL) performance. The X-ray diffraction, atomic force microscopy, and EL mechanisms indicate that the p-GaN/n-ZnO nanorod with magnetron-sputtering ZnO nanoseeds has a better crystalline interface. Our results indicate that the p-GaN/n-ZnO nanorod/CsPbBr3 QDs heterojunction structure can be served as dual-wavelength LEDs, and magnetron-sputtering ZnO nanoseeds can give rise to a better EL performance.