Special Issue "Optoelectronic Nanodevices"

A special issue of Nanomaterials (ISSN 2079-4991).

Deadline for manuscript submissions: closed (30 November 2018).

Special Issue Editor

Guest Editor
Dr. Minas M. Stylianakis

Hellenic Mediterranean University (HMU), Department of Electrical & Computer Engineering Estavromenos P.B 1939, Heraklion, GR-71410, Crete, Greece
Website | E-Mail
Interests: graphene; 2D nanomaterials; metal oxides; materials science; chemistry; energy applications; organic photovoltaics; perovskite solar cells

Special Issue Information

Dear Colleagues,

Over the last decade, graphene and beyond graphene nanomaterials (TMDs, Xenes) have centralized the interest of the scientific community, due to the extraordinary physical, optical, thermal, and electrical properties, which are correlated with their two-dimensional (2D) ultrathin atomic layer structure, large interlayer distance, ease of functionalization, as well as tunable bandgap. Therefore, potential applications in the fastest growing fields of energy (photovoltaics, energy storage, fuel cells, hydrogen storage, catalysis, etc.), electronics, photonics, spintronics and sensing have been developed. The continuous nanostructure-based applications development offers the confidence to significantly improve existing products and to enable the design of materials and devices with novel functionalities.

We invite investigators to submit original research articles, letters, as well as review articles and perspective views, on fundamental studies and optoelectronic applications of nanomaterials. The present Special Issue of Nanomaterials focuses on new insights demonstration, as well as the potential and challenges in the realization of various efficient optoelectronic devices, such as solar cells (OSCs, PeSCs), light emitting diodes (LEDs), sensors, photodetectors, etc., upon the incorporation of nanostructured materials.

Dr. Minas M. Stylianakis
Guest Editor

Manuscript Submission Information

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Keywords

  • Nanomaterials
  • Optoelectronic devices
  • Light Emitting Diodes
  • Solar Cells
  • Electronics
  • Photonics

Published Papers (25 papers)

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Open AccessArticle
Effect of Excitation Wavelength on Optical Performances of Quantum-Dot-Converted Light-Emitting Diode
Nanomaterials 2019, 9(8), 1100; https://doi.org/10.3390/nano9081100
Received: 10 July 2019 / Revised: 24 July 2019 / Accepted: 25 July 2019 / Published: 1 August 2019
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Abstract
Light-emitting diode (LED) combined with quantum dots (QDs) is an important candidate for next-generation high-quality semiconductor devices. However, the effect of the excitation wavelength on their optical performance has not been fully explored. In this study, green and red QDs are applied to [...] Read more.
Light-emitting diode (LED) combined with quantum dots (QDs) is an important candidate for next-generation high-quality semiconductor devices. However, the effect of the excitation wavelength on their optical performance has not been fully explored. In this study, green and red QDs are applied to LEDs of different excitation wavelengths from 365 to 455 nm. The blue light is recommended for exciting QDs from the perspective of energy utilization. However, QD LEDs excited at 365 nm have unique advantages in eliminating the original peaks from the LED chip. Moreover, the green or red light excited by ultraviolet light has an advantage in colorimetry. Even for the 455 nm LED with the highest QD concentration at 7.0 wt%, the color quality could not compete with the 365 nm LED with the lowest QD concentration at 0.2 wt%. A 117.5% (NTSC1953) color gamut could be obtained by the 365 nm-excited RGB system, which is 32.6% higher than by the 455 nm-excited solution, and this can help expand the color gamut of LED devices. Consequently, this study provides an understanding of the properties of QD-converted LEDs under different wavelength excitations, and offers a general guide to selecting a pumping source for QDs. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Room Temperature Resonant Photocurrent in an Erbium Low-Doped Silicon Transistor at Telecom Wavelength
Nanomaterials 2019, 9(3), 416; https://doi.org/10.3390/nano9030416
Received: 1 February 2019 / Revised: 1 March 2019 / Accepted: 5 March 2019 / Published: 11 March 2019
Cited by 1 | PDF Full-text (1325 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
An erbium-doped silicon transistor prepared by ion implantation and co-doped with oxygen is investigated by photocurrent generation in the telecommunication range. The photocurrent is explored at room temperature as a function of the wavelength by using a supercontinuum laser source working in the [...] Read more.
An erbium-doped silicon transistor prepared by ion implantation and co-doped with oxygen is investigated by photocurrent generation in the telecommunication range. The photocurrent is explored at room temperature as a function of the wavelength by using a supercontinuum laser source working in the μW range. The 1-μm2 transistor is tuned to involve in the transport only those electrons lying in the Er-O states. The spectrally resolved photocurrent is characterized by the typical absorption line of erbium and the linear dependence of the signal over the impinging power demonstrates that the Er-doped transistor is operating far from saturation. The relatively small number of estimated photoexcited atoms (≈ 4 × 10 4 ) makes Er-dpoed silicon potentially suitable for designing resonance-based frequency selective single photon detectors at 1550 nm. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Enhanced Light Extraction of Flip-Chip Mini-LEDs with Prism-Structured Sidewall
Nanomaterials 2019, 9(3), 319; https://doi.org/10.3390/nano9030319
Received: 22 January 2019 / Revised: 24 February 2019 / Accepted: 26 February 2019 / Published: 28 February 2019
Cited by 4 | PDF Full-text (4957 KB) | HTML Full-text | XML Full-text
Abstract
Current solutions for improving the light extraction efficiency of flip-chip light-emitting diodes (LEDs) mainly focus on relieving the total internal reflection at sapphire/air interface, but such methods hardly affect the epilayer mode photons. We demonstrated that the prism-structured sidewall based on tetramethylammonium hydroxide [...] Read more.
Current solutions for improving the light extraction efficiency of flip-chip light-emitting diodes (LEDs) mainly focus on relieving the total internal reflection at sapphire/air interface, but such methods hardly affect the epilayer mode photons. We demonstrated that the prism-structured sidewall based on tetramethylammonium hydroxide (TMAH) etching is a cost-effective solution for promoting light extraction efficiency of flip-chip mini-LEDs. The anisotropic TMAH etching created hierarchical prism structure on sidewall of mini-LEDs for coupling out photons into air without deteriorating the electrical property. Prism-structured sidewall effectively improved light output power of mini-LEDs by 10.3%, owing to the scattering out of waveguided light trapped in the gallium nitride (GaN) epilayer. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Improvement in Light Output of Ultraviolet Light-Emitting Diodes with Patterned Double-Layer ITO by Laser Direct Writing
Nanomaterials 2019, 9(2), 203; https://doi.org/10.3390/nano9020203
Received: 7 January 2019 / Revised: 30 January 2019 / Accepted: 30 January 2019 / Published: 4 February 2019
Cited by 3 | PDF Full-text (3485 KB) | HTML Full-text | XML Full-text
Abstract
A patterned double-layer indium-tin oxide (ITO), including the first unpatterned ITO layer serving as current spreading and the second patterned ITO layer serving as light extracting, was applied to obtain uniform current spreading and high light extraction efficiency (LEE) of GaN-based ultraviolet (UV) [...] Read more.
A patterned double-layer indium-tin oxide (ITO), including the first unpatterned ITO layer serving as current spreading and the second patterned ITO layer serving as light extracting, was applied to obtain uniform current spreading and high light extraction efficiency (LEE) of GaN-based ultraviolet (UV) light-emitting diodes (LEDs). Periodic pinhole patterns were formed on the second ITO layer by laser direct writing to increase the LEE of UV LED. Effects of interval of pinhole patterns on optical and electrical properties of UV LED with patterned double-layer ITO were studied by numerical simulations and experimental investigations. Due to scattering out of waveguided light trapped inside the GaN film, LEE of UV LED with patterned double-layer ITO was improved as compared to UV LED with planar double-layer ITO. As interval of pinhole patterns decreased, the light output power (LOP) of UV LED with patterned double-layer ITO increased. In addition, UV LED with patterned double-layer ITO exhibited a slight degradation of current spreading as compared to the UV LED with a planar double-layer ITO. The forward voltage of UV LED with patterned double-layer ITO increased as the interval of pinhole patterns decreased. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Arrayed CdTeMicrodots and Their Enhanced Photodetectivity via Piezo-Phototronic Effect
Nanomaterials 2019, 9(2), 178; https://doi.org/10.3390/nano9020178
Received: 27 November 2018 / Revised: 21 January 2019 / Accepted: 23 January 2019 / Published: 1 February 2019
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Abstract
In this paper, a photodetector based on arrayed CdTe microdots was fabricated on Bi coated transparent conducting indium tin oxide (ITO)/glass substrates. Current-voltage characteristics of these photodetectors revealed an ultrahigh sensitivity under stress (in the form of force through press) while compared to [...] Read more.
In this paper, a photodetector based on arrayed CdTe microdots was fabricated on Bi coated transparent conducting indium tin oxide (ITO)/glass substrates. Current-voltage characteristics of these photodetectors revealed an ultrahigh sensitivity under stress (in the form of force through press) while compared to normal condition. The devices exhibited excellent photosensing properties with photoinduced current increasing from 20 to 76 μA cm−2 under stress. Furthermore, the photoresponsivity of the devices also increased under stress from 3.2 × 10−4 A/W to 5.5 × 10−3 A/W at a bias of 5 V. The observed characteristics are attributed to the piezopotential induced change in Schottky barrier height, which actually results from the piezo-phototronic effect. The obtained results also demonstrate the feasibility in realization of a facile and promising CdTe microdots-based photodetector via piezo-phototronic effect. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Updating the Role of Reduced Graphene Oxide Ink on Field Emission Devices in Synergy with Charge Transfer Materials
Nanomaterials 2019, 9(2), 137; https://doi.org/10.3390/nano9020137
Received: 10 December 2018 / Revised: 2 January 2019 / Accepted: 14 January 2019 / Published: 22 January 2019
Cited by 2 | PDF Full-text (4636 KB) | HTML Full-text | XML Full-text
Abstract
Hydroiodic acid (HI)-treated reduced graphene oxide (rGO) ink/conductive polymeric composites are considered as promising cold cathodes in terms of high geometrical aspect ratio and low field emission (FE) threshold devices. In this study, four simple, cost-effective, solution-processed approaches for rGO-based field effect emitters [...] Read more.
Hydroiodic acid (HI)-treated reduced graphene oxide (rGO) ink/conductive polymeric composites are considered as promising cold cathodes in terms of high geometrical aspect ratio and low field emission (FE) threshold devices. In this study, four simple, cost-effective, solution-processed approaches for rGO-based field effect emitters were developed, optimized, and compared; rGO layers were coated on (a) n+ doped Si substrate, (b) n+-Si/P3HT:rGO, (c) n+-Si/PCDTBT:rGO, and (d) n+-Si/PCDTBT:PC71BM:rGO composites, respectively. The fabricated emitters were optimized by tailoring the concentration ratios of their preparation and field emission characteristics. In a critical composite ratio, FE performance was remarkably improved compared to the pristine Si, as well as n+-Si/rGO field emitter. In this context, the impact of various materials, such as polymers, fullerene derivatives, as well as different solvents on rGO function reinforcement and consequently on FE performance upon rGO-based composites preparation was investigated. The field emitter consisted of n+-Si/PCDTBT:PC71BM(80%):rGO(20%)/rGO displayed a field enhancement factor of ~2850, with remarkable stability over 20 h and low turn-on field in 0.6 V/μm. High-efficiency graphene-based FE devices realization paves the way towards low-cost, large-scale electron sources development. Finally, the contribution of this hierarchical, composite film morphology was evaluated and discussed. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Dynamically Tunable Light Absorbers as Color Filters Based on Electrowetting Technology
Nanomaterials 2019, 9(1), 70; https://doi.org/10.3390/nano9010070
Received: 21 November 2018 / Revised: 26 December 2018 / Accepted: 31 December 2018 / Published: 6 January 2019
Cited by 1 | PDF Full-text (1623 KB) | HTML Full-text | XML Full-text
Abstract
A device that uses the electrowetting fluid manipulation technology to realize the reversible and dynamical modulation of the local surface plasmon resonance is invented. By varying the electrowetting voltage, the distribution of fluids media surrounding the grating structure get changed accordingly, causing the [...] Read more.
A device that uses the electrowetting fluid manipulation technology to realize the reversible and dynamical modulation of the local surface plasmon resonance is invented. By varying the electrowetting voltage, the distribution of fluids media surrounding the grating structure get changed accordingly, causing the modulation of the plasmonic resonance peak. The simulation results indicated that three primary colors, that are cyan, magenta and yellow (CMY) can be respectively reflected through selecting suitable structural parameters. More importantly, for the first time, the invented fluid-based devices have exhibited fine-tuning characteristics for each primary color. Finally, the device has been proved to have a large color gamut range in the Commission International De L’E’clairage (CIE) 1931 color space. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Fabrication and Characterization of AlGaN-Based UV LEDs with a ITO/Ga2O3/Ag/Ga2O3 Transparent Conductive Electrode
Nanomaterials 2019, 9(1), 66; https://doi.org/10.3390/nano9010066
Received: 30 November 2018 / Revised: 27 December 2018 / Accepted: 31 December 2018 / Published: 5 January 2019
Cited by 2 | PDF Full-text (2744 KB) | HTML Full-text | XML Full-text
Abstract
We fabricated a complex transparent conductive electrode (TCE) based on Ga2O3 for AlGaN-based ultraviolet light-emitting diodes. The complex TCE consists of a 10 nm ITO, a 15 nm Ga2O3, a 7 nm Ag, and a 15 [...] Read more.
We fabricated a complex transparent conductive electrode (TCE) based on Ga2O3 for AlGaN-based ultraviolet light-emitting diodes. The complex TCE consists of a 10 nm ITO, a 15 nm Ga2O3, a 7 nm Ag, and a 15 nm Ga2O3, forming a ITO/Ga2O3/Ag/Ga2O3 multilayer. The metal layer embedded into Ga2O3 and the thin ITO contact layer improves current spreading and electrode contact properties. It is found that the ITO/Ga2O3/Ag/Ga2O3 multilayer can reach a 92.8% transmittance at 365 nm and a specific contact resistance of 10−3 Ω·cm2 with suitable annealing conditions. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Tunable Metamaterial with Gold and Graphene Split-Ring Resonators and Plasmonically Induced Transparency
Nanomaterials 2019, 9(1), 7; https://doi.org/10.3390/nano9010007
Received: 28 November 2018 / Revised: 16 December 2018 / Accepted: 20 December 2018 / Published: 21 December 2018
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Abstract
In this paper, we propose a metamaterial structure for realizing the electromagnetically induced transparency effect in the MIR region, which consists of a gold split-ring and a graphene split-ring. The simulated results indicate that a single tunable transparency window can be realized in [...] Read more.
In this paper, we propose a metamaterial structure for realizing the electromagnetically induced transparency effect in the MIR region, which consists of a gold split-ring and a graphene split-ring. The simulated results indicate that a single tunable transparency window can be realized in the structure due to the hybridization between the two rings. The transparency window can be tuned individually by the coupling distance and/or the Fermi level of the graphene split-ring via electrostatic gating. These results could find significant applications in nanoscale light control and functional devices operating such as sensors and modulators. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Enhancing GaN LED Efficiency through Nano-Gratings and Standing Wave Analysis
Nanomaterials 2018, 8(12), 1045; https://doi.org/10.3390/nano8121045
Received: 16 November 2018 / Revised: 30 November 2018 / Accepted: 10 December 2018 / Published: 13 December 2018
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Abstract
Based on our recent work, this paper reviews our theoretical study on gallium nitride (GaN) light-emitting-diode (LED). The focus of the paper is to improve LED light extraction efficiency through various nano-grating designs. The gratings can be designed at different locations, such as [...] Read more.
Based on our recent work, this paper reviews our theoretical study on gallium nitride (GaN) light-emitting-diode (LED). The focus of the paper is to improve LED light extraction efficiency through various nano-grating designs. The gratings can be designed at different locations, such as at the top, the middle, and the bottom, on the LED. They also can be made of different materials. In this study, we first present a GaN LED error-grating simulation model. Second, nano Indium Tin Oxide (ITO) top gratings are studied and compared with conventional LED (CLED) using standing wave analysis. Third, we present results related to a patterned sapphire substrate (PSS), SiO2 Nanorod array (NR), and Ag bottom reflection layer. Finally, we investigate the nano-top ITO grating performance over different wavelengths to validate our design simulation, which focusing on a single wavelength of 460 nm. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Significant Carrier Extraction Enhancement at the Interface of an InN/p-GaN Heterojunction under Reverse Bias Voltage
Nanomaterials 2018, 8(12), 1039; https://doi.org/10.3390/nano8121039
Received: 23 October 2018 / Revised: 6 December 2018 / Accepted: 10 December 2018 / Published: 12 December 2018
Cited by 1 | PDF Full-text (1811 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a superior-quality InN/p-GaN interface grown using pulsed metalorganic vapor-phase epitaxy (MOVPE) is demonstrated. The InN/p-GaN heterojunction interface based on high-quality InN (electron concentration 5.19 × 1018 cm−3 and mobility 980 cm2/(V s)) showed good rectifying behavior. [...] Read more.
In this paper, a superior-quality InN/p-GaN interface grown using pulsed metalorganic vapor-phase epitaxy (MOVPE) is demonstrated. The InN/p-GaN heterojunction interface based on high-quality InN (electron concentration 5.19 × 1018 cm−3 and mobility 980 cm2/(V s)) showed good rectifying behavior. The heterojunction depletion region width was estimated to be 22.8 nm and showed the ability for charge carrier extraction without external electrical field (unbiased). Under reverse bias, the external quantum efficiency (EQE) in the blue spectral region (300–550 nm) can be enhanced significantly and exceeds unity. Avalanche and carrier multiplication phenomena were used to interpret the exclusive photoelectric features of the InN/p-GaN heterojunction behavior. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Enhancing Output Power of Textured Silicon Solar Cells by Embedding Indium Plasmonic Nanoparticles in Layers within Antireflective Coating
Nanomaterials 2018, 8(12), 1003; https://doi.org/10.3390/nano8121003
Received: 15 November 2018 / Revised: 30 November 2018 / Accepted: 30 November 2018 / Published: 4 December 2018
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Abstract
In this study, we sought to enhance the output power and conversion efficiency of textured silicon solar cells by layering two-dimensional indium nanoparticles (In NPs) within a double-layer (SiNx/SiO2) antireflective coating (ARC) to induce plasmonic forward scattering. The plasmonic [...] Read more.
In this study, we sought to enhance the output power and conversion efficiency of textured silicon solar cells by layering two-dimensional indium nanoparticles (In NPs) within a double-layer (SiNx/SiO2) antireflective coating (ARC) to induce plasmonic forward scattering. The plasmonic effects were characterized using Raman scattering, absorbance spectra, optical reflectance, and external quantum efficiency. We compared the optical and electrical performance of cells with and without single layers and double layers of In NPs. The conversion efficiency of the cell with a double layer of In NPs (16.97%) was higher than that of the cell with a single layer of In NPs (16.61%) and greatly exceeded that of the cell without In NPs (16.16%). We also conducted a comprehensive study on the light-trapping performance of the textured silicon solar cells with and without layers of In NPs within the double layer of ARC at angles from 0° to 75°. The total electrical output power of cells under air mass (AM) 1.5 G illumination was calculated. The application of a double layer of In NPs enabled an impressive 53.42% improvement in electrical output power (compared to the cell without NPs) thanks to the effects of plasmonic forward scattering. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
A Compact and Smooth CH3NH3PbI3 Film: Investigation of Solvent Sorts and Concentrations of CH3NH3I towards Highly Efficient Perovskite Solar Cells
Nanomaterials 2018, 8(11), 897; https://doi.org/10.3390/nano8110897
Received: 10 October 2018 / Revised: 27 October 2018 / Accepted: 29 October 2018 / Published: 1 November 2018
Cited by 1 | PDF Full-text (2111 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Four solvents (isopropanol (IPA), n-butyl alcohol (NBA), n-amyl alcohol (NAA), and n-hexyl alcohol (NHA)) were investigated to prepare CH3NH3I (methylammonium iodide, MAI) solutions to transform PbI2 film into CH3NH3PbI3 (MAPbI [...] Read more.
Four solvents (isopropanol (IPA), n-butyl alcohol (NBA), n-amyl alcohol (NAA), and n-hexyl alcohol (NHA)) were investigated to prepare CH3NH3I (methylammonium iodide, MAI) solutions to transform PbI2 film into CH3NH3PbI3 (MAPbI3) film. It was found that the morphology of the perovskite MAPbI3 film was not only affected by the chain of the solvent molecule, but also by the concentration of MAI. The use of solvents with a long alkyl chain (NAA and NHA) allowed the MAPbI3 to grow via an in situ transformation step, which easily made the perovskite films compact, but with a high surface roughness due to the growth of unexpected nanorods/nanoplates. The solvent with a short alkyl chain (IPA) led to the dissolution−crystallization growth mechanism, resulting in rapid generation of perovskite films with a number of pinholes. A high-quality (compact, smooth, pinhole-free) perovskite film was obtained with NBA and an optimized MAI concentration of 8 mg/mL. The corresponding perovskite solar cells achieved a maximum power conversion efficiency (PCE) of 16.66% and average PCE of 14.76% (for 40 cells). Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Controllable Synthesis of 2D Perovskite on Different Substrates and Its Application as Photodetector
Nanomaterials 2018, 8(8), 591; https://doi.org/10.3390/nano8080591
Received: 14 June 2018 / Revised: 12 July 2018 / Accepted: 12 July 2018 / Published: 3 August 2018
Cited by 4 | PDF Full-text (16266 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Perovskites have recently attracted intense interests for optoelectronic devices application due to their excellent photovoltaic and photoelectric properties. The performance of perovskite-based devices highly depends on the perovskite material properties. However, the widely used spin-coating method can only prepare polycrystalline perovskite and physical [...] Read more.
Perovskites have recently attracted intense interests for optoelectronic devices application due to their excellent photovoltaic and photoelectric properties. The performance of perovskite-based devices highly depends on the perovskite material properties. However, the widely used spin-coating method can only prepare polycrystalline perovskite and physical vapor deposition (PVD) method requires a higher melting point (>350 °C) substrate due to the high growth temperature, which is not suitable for low melting point substrates, especially for flexible substrates. Here, we present the controlled synthesis of high quality two-dimensional (2D) perovskite platelets on random substrates, including SiO2/Si, Si, mica, glass and flexible polydimethylsiloxane (PDMS) substrates, and our method is applicable to any substrate as long as its melting point is higher than 100 °C. We found that the photoluminescence (PL) characteristics of perovskite depend strongly on the platelets thickness, namely, thicker perovskite platelet has higher PL wavelength and stronger intensity, and thinner perovskite exhibits opposite results. Moreover, photodetectors based on the as-produced perovskite platelets show excellent photoelectric performance with a high photoresponsivity of 8.3 A·W−1, a high on/off ratio of ~103, and a small rise and decay time of 30 and 50 ms, respectively. Our approach in this work provides a feasible way for making 2D perovskite platelets for wide optoelectronic applications. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Quantum Efficiency Enhancement of a GaN-Based Green Light-Emitting Diode by a Graded Indium Composition p-Type InGaN Layer
Nanomaterials 2018, 8(7), 512; https://doi.org/10.3390/nano8070512
Received: 27 May 2018 / Revised: 28 June 2018 / Accepted: 7 July 2018 / Published: 9 July 2018
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Abstract
We propose a graded indium composition p-type InGaN (p-InGaN) conduction layer to replace the p-type AlGaN electron blocking layer and a p-GaN layer in order to enhance the light output power of a GaN-based green light-emitting diode (LED). The indium composition of the [...] Read more.
We propose a graded indium composition p-type InGaN (p-InGaN) conduction layer to replace the p-type AlGaN electron blocking layer and a p-GaN layer in order to enhance the light output power of a GaN-based green light-emitting diode (LED). The indium composition of the p-InGaN layer decreased from 10.4% to 0% along the growth direction. The light intensity of the LED with a graded indium composition p-InGaN layer is 13.7% higher than that of conventional LEDs according to the experimental result. The calculated data further confirmed that the graded indium composition p-InGaN layer can effectively improve the light power of green LEDs. According to the simulation, the increase in light output power of green LEDs with a graded indium composition p-InGaN layer was mainly attributed to the enhancement of hole injection and the improvement of the radiative recombination rate. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Improvement in Color-Conversion Efficiency and Stability for Quantum-Dot-Based Light-Emitting Diodes Using a Blue Anti-Transmission Film
Nanomaterials 2018, 8(7), 508; https://doi.org/10.3390/nano8070508
Received: 8 June 2018 / Revised: 27 June 2018 / Accepted: 2 July 2018 / Published: 9 July 2018
Cited by 2 | PDF Full-text (3129 KB) | HTML Full-text | XML Full-text
Abstract
In this report, a blue anti-transmission film (BATF) has been introduced to improve the color-conversion efficiency (CCE) and the stability of quantum dot (QD) films. The results indicate that the CCE can be increased by as much as 93% using 15 layers of [...] Read more.
In this report, a blue anti-transmission film (BATF) has been introduced to improve the color-conversion efficiency (CCE) and the stability of quantum dot (QD) films. The results indicate that the CCE can be increased by as much as 93% using 15 layers of BATFs under the same QD concentration. Therefore, the same CCE can be achieved using BATF-QD hybrid films with a lower QD concentration when compared with standard QD films. The hybrid and QD films with the same CCE of 60% were aged at an environmental temperature of 25°C and with a 10 mA injection current light-emitting diode source. The CCE and luminous efficacy that are gained by the hybrid film increased by 42.8% and 24.5%, respectively, when compared with that gained by the QD film after aging for the same time period of approximately 65 h. In addition, the hybrid film can effectively suppress the red-shift phenomenon of the QD light spectra, as well as an expansion of the full-width at half maximum. Consequently, these BATF-QD hybrid films with excellent optical performance and stability show great potential for illumination and display applications. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Effects of Different Oxidation Degrees of Graphene Oxide on P-Type and N-Type Si Heterojunction Photodetectors
Nanomaterials 2018, 8(7), 491; https://doi.org/10.3390/nano8070491
Received: 25 May 2017 / Revised: 29 June 2018 / Accepted: 2 July 2018 / Published: 4 July 2018
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Abstract
Oxygen-containing functional groups in graphene oxide (GO), a derivative of graphene, can widen the bandgap of graphene. In this study, we varied the amount of hydrogen peroxide used to prepare GO samples with different degrees of oxidation. Transmittance measurement, Raman spectroscopy, and X-ray [...] Read more.
Oxygen-containing functional groups in graphene oxide (GO), a derivative of graphene, can widen the bandgap of graphene. In this study, we varied the amount of hydrogen peroxide used to prepare GO samples with different degrees of oxidation. Transmittance measurement, Raman spectroscopy, and X-ray photoelectron spectroscopy were used to completely characterize the change in oxidation degree. The effects of oxidation degree on p-type and n-type Si heterojunction photodetectors were compared. Notably, GO with a lower oxidation degree led to a larger photoresponse of p-type Si, whereas that with a higher oxidation degree achieved a larger photoresponse of n-type Si. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
High Performance Ultrathin MoO3/Ag Transparent Electrode and Its Application in Semitransparent Organic Solar Cells
Nanomaterials 2018, 8(7), 473; https://doi.org/10.3390/nano8070473
Received: 10 June 2018 / Revised: 22 June 2018 / Accepted: 24 June 2018 / Published: 27 June 2018
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Abstract
In this paper, we demonstrate high performance ultrathin silver (Ag) transparent electrodes with a thin MoO3 nucleation layer based on the thermal evaporation method. The MoO3/Ag transparent electrodes fabricated at different deposition rates were compared systematically on aspects of the [...] Read more.
In this paper, we demonstrate high performance ultrathin silver (Ag) transparent electrodes with a thin MoO3 nucleation layer based on the thermal evaporation method. The MoO3/Ag transparent electrodes fabricated at different deposition rates were compared systematically on aspects of the transmission spectrum, surface resistance, and surface morphology. Our study indicates that with the presence of the MoO3 nucleation layer, an Ag film of only 7 nm thick can achieve percolation and the film is porous instead of forming isolated islands. In addition, the increase of the deposition rate can yield obvious improvement of the surface morphology of the Ag film. Specifically, with the help of a 1 nm thick MoO3 nucleation layer, the Ag film of 9 nm thick realized under the deposition rate of 0.7 nm/s has a surface resistance of about 20 ohm/sq and an average transmittance in the visible light range reaching 74.22%. Such a high performance of transmittance is superior to the reported results in the literature, which inevitably suffer obvious drop in the long wavelength range. Next, we applied the ultrathin MoO3/Ag transparent electrode in organic solar cells. The optimized semitransparent organic solar cell displays a power conversion efficiency of 2.76% and an average transmittance in the visible range of 38% when light is incident from the Ag electrode side. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Improved Performance of Perovskite Light-Emitting Diodes by Quantum Confinement Effect in Perovskite Nanocrystals
Nanomaterials 2018, 8(7), 459; https://doi.org/10.3390/nano8070459
Received: 25 May 2018 / Revised: 15 June 2018 / Accepted: 19 June 2018 / Published: 25 June 2018
Cited by 1 | PDF Full-text (2990 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this study, we demonstrate an easy and reliable solution-processed technique using an extra adductive in the perovskite precursor solution. Using this method, a dense and uniform morphology with full surface coverage and highly fluorescent films with nanoscale crystal grains can be obtained. [...] Read more.
In this study, we demonstrate an easy and reliable solution-processed technique using an extra adductive in the perovskite precursor solution. Using this method, a dense and uniform morphology with full surface coverage and highly fluorescent films with nanoscale crystal grains can be obtained. The high exciton binding energy in the resulting films employing octylammonium bromide (OAB) adductives proved that high fluorescence originated from the quantum confinement effect. The corresponding perovskite light-emitting diodes (PeLEDs) that were based on this technique also exhibited excellent device performance. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
An InGaN/GaN Superlattice to Enhance the Performance of Green LEDs: Exploring the Role of V-Pits
Nanomaterials 2018, 8(7), 450; https://doi.org/10.3390/nano8070450
Received: 15 May 2018 / Revised: 8 June 2018 / Accepted: 18 June 2018 / Published: 21 June 2018
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Abstract
Despite the fact that an InGaN/GaN superlattice (SL) is useful for enhancing the performance of a GaN-based light-emitting diode (LED), its role in improving the efficiency of green LEDs remains an open question. Here, we investigate the influence of a V-pits-embedded InGaN/GaN SL [...] Read more.
Despite the fact that an InGaN/GaN superlattice (SL) is useful for enhancing the performance of a GaN-based light-emitting diode (LED), its role in improving the efficiency of green LEDs remains an open question. Here, we investigate the influence of a V-pits-embedded InGaN/GaN SL on optical and electrical properties of GaN-based green LEDs. We recorded a sequence of light emission properties of InGaN/GaN multiple quantum wells (MQWs) grown on a 0- and 24-pair InGaN/GaN SL by using scanning electron microscopy (SEM) in combination with a room temperature cathodoluminescence (CL) measurement, which demonstrated the presence of a potential barrier formed by the V-pits around threading dislocations (TDs). We find that an increase in V-pit diameter would lead to the increase of V-pit potential barrier height. Our experimental data suggest that a V-pits-embedded, 24-pair InGaN/GaN SL can effectively suppress the lateral diffusion of carriers into non-recombination centers. As a result, the external quantum efficiency (EQE) of green LEDs is improved by 29.6% at an injection current of 20 mA after implementing the V-pits-embedded InGaN/GaN SL layer. In addition, a lower reverse leakage current was achieved with larger V-pits. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
High-Efficiency Visible Transmitting Polarizations Devices Based on the GaN Metasurface
Nanomaterials 2018, 8(5), 333; https://doi.org/10.3390/nano8050333
Received: 29 April 2018 / Revised: 9 May 2018 / Accepted: 10 May 2018 / Published: 15 May 2018
Cited by 11 | PDF Full-text (14171 KB) | HTML Full-text | XML Full-text
Abstract
Metasurfaces are capable of tailoring the amplitude, phase, and polarization of incident light to design various polarization devices. Here, we propose a metasurface based on the novel dielectric material gallium nitride (GaN) to realize high-efficiency modulation for both of the orthogonal linear polarizations [...] Read more.
Metasurfaces are capable of tailoring the amplitude, phase, and polarization of incident light to design various polarization devices. Here, we propose a metasurface based on the novel dielectric material gallium nitride (GaN) to realize high-efficiency modulation for both of the orthogonal linear polarizations simultaneously in the visible range. Both modulated transmitted phases of the orthogonal linear polarizations can almost span the whole 2π range by tailoring geometric sizes of the GaN nanobricks, while maintaining high values of transmission (almost all over 90%). At the wavelength of 530 nm, we designed and realized the beam splitter and the focusing lenses successfully. To further prove that our proposed method is suitable for arbitrary orthogonal linear polarization, we also designed a three-dimensional (3D) metalens that can simultaneously focus the X-, Y-, 45°, and 135° linear polarizations on spatially symmetric positions, which can be applied to the linear polarization measurement. Our work provides a possible method to achieve high-efficiency multifunctional optical devices in visible light by extending the modulating dimensions. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Ti Porous Film-Supported NiCo2S4 Nanotubes Counter Electrode for Quantum-Dot-Sensitized Solar Cells
Nanomaterials 2018, 8(4), 251; https://doi.org/10.3390/nano8040251
Received: 22 March 2018 / Revised: 13 April 2018 / Accepted: 13 April 2018 / Published: 17 April 2018
Cited by 4 | PDF Full-text (25810 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a novel Ti porous film-supported NiCo2S4 nanotube was fabricated by the acid etching and two-step hydrothermal method and then used as a counter electrode in a CdS/CdSe quantum-dot-sensitized solar cell. Measurements of the cyclic voltammetry, Tafel polarization [...] Read more.
In this paper, a novel Ti porous film-supported NiCo2S4 nanotube was fabricated by the acid etching and two-step hydrothermal method and then used as a counter electrode in a CdS/CdSe quantum-dot-sensitized solar cell. Measurements of the cyclic voltammetry, Tafel polarization curves, and electrochemical impedance spectroscopy of the symmetric cells revealed that compared with the conventional FTO (fluorine doped tin oxide)/Pt counter electrode, Ti porous film-supported NiCo2S4 nanotubes counter electrode exhibited greater electrocatalytic activity toward polysulfide electrolyte and lower charge-transfer resistance at the interface between electrolyte and counter electrode, which remarkably improved the fill factor, short-circuit current density, and power conversion efficiency of the quantum-dot-sensitized solar cell. Under illumination of one sun (100 mW/cm2), the quantum-dot-sensitized solar cell based on Ti porous film-supported NiCo2S4 nanotubes counter electrode achieved a power conversion efficiency of 3.14%, which is superior to the cell based on FTO/Pt counter electrode (1.3%). Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessArticle
Study on the Coupling Mechanism of the Orthogonal Dipoles with Surface Plasmon in Green LED by Cathodoluminescence
Nanomaterials 2018, 8(4), 244; https://doi.org/10.3390/nano8040244
Received: 23 March 2018 / Revised: 12 April 2018 / Accepted: 12 April 2018 / Published: 16 April 2018
Cited by 1 | PDF Full-text (7593 KB) | HTML Full-text | XML Full-text
Abstract
We analyzed the coupling behavior between the localized surface plasmon (LSP) and quantum wells (QWs) using cathodoluminescence (CL) in a green light-emitting diodes (LED) with Ag nanoparticles (NPs) filled in photonic crystal (PhC) holes. Photoluminescence (PL) suppression and CL enhancement were obtained for [...] Read more.
We analyzed the coupling behavior between the localized surface plasmon (LSP) and quantum wells (QWs) using cathodoluminescence (CL) in a green light-emitting diodes (LED) with Ag nanoparticles (NPs) filled in photonic crystal (PhC) holes. Photoluminescence (PL) suppression and CL enhancement were obtained for the same green LED sample with the Ag NP array. Time-resolved PL (TRPL) results indicate strong coupling between the LSP and the QWs. Three-dimensional (3D) finite difference time domain (FDTD) simulation was performed using a three-body model consisting of two orthogonal dipoles and a single Ag NP. The LSP–QWs coupling effect was separated from the electron-beam (e-beam)–LSP–QW system by linear approximation. The energy dissipation was significantly reduced by the z-dipole introduction under the e-beam excitation. In this paper, the coupling mechanism is discussed and a novel emission structure is proposed. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Review

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Open AccessReview
Liquid Crystal Enabled Dynamic Nanodevices
Nanomaterials 2018, 8(11), 871; https://doi.org/10.3390/nano8110871
Received: 26 September 2018 / Revised: 13 October 2018 / Accepted: 20 October 2018 / Published: 23 October 2018
Cited by 2 | PDF Full-text (6336 KB) | HTML Full-text | XML Full-text
Abstract
Inspired by the anisotropic molecular shape and tunable alignment of liquid crystals (LCs), investigations on hybrid nanodevices which combine LCs with plasmonic metasurfaces have received great attention recently. Since LCs possess unique electro-optical properties, developing novel dynamic optical components by incorporating nematic LCs [...] Read more.
Inspired by the anisotropic molecular shape and tunable alignment of liquid crystals (LCs), investigations on hybrid nanodevices which combine LCs with plasmonic metasurfaces have received great attention recently. Since LCs possess unique electro-optical properties, developing novel dynamic optical components by incorporating nematic LCs with nanostructures offers a variety of practical applications. Owing to the large birefringence of LCs, the optical properties of metamaterials can be electrically or optically modulated over a wide range. In this review article, we show different elegant designs of metasurface based nanodevices integrated into LCs and explore the tuning factors of transmittance/extinction/scattering spectra. Moreover, we review and classify substantial tunable devices enabled by LC-plasmonic interactions. These dynamically tunable optoelectronic nanodevices and components are of extreme importance, since they can enable a significant range of applications, including ultra-fast switching, modulating, sensing, imaging, and waveguiding. By integrating LCs with two dimensional metasurfaces, one can manipulate electromagnetic waves at the nanoscale with dramatically reduced sizes. Owing to their special electro-optical properties, recent efforts have demonstrated that more accurate manipulation of LC-displays can be engineered by precisely controlling the alignment of LCs inside small channels. In particular, device performance can be significantly improved by optimizing geometries and the surrounding environmental parameters. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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Open AccessReview
Research Progress in Organic Photomultiplication Photodetectors
Nanomaterials 2018, 8(9), 713; https://doi.org/10.3390/nano8090713
Received: 31 July 2018 / Revised: 28 August 2018 / Accepted: 31 August 2018 / Published: 11 September 2018
Cited by 5 | PDF Full-text (2025 KB) | HTML Full-text | XML Full-text
Abstract
Organic photomultiplication photodetectors have attracted considerable research interest due to their extremely high external quantum efficiency and corresponding high detectivity. Significant progress has been made in the aspects of their structural design and performance improvement in the past few years. There are two [...] Read more.
Organic photomultiplication photodetectors have attracted considerable research interest due to their extremely high external quantum efficiency and corresponding high detectivity. Significant progress has been made in the aspects of their structural design and performance improvement in the past few years. There are two types of organic photomultiplication photodetectors, which are made of organic small molecular compounds and polymers. In this paper, the research progress in each type of organic photomultiplication photodetectors based on the trap assisted carrier tunneling effect is reviewed in detail. In addition, other mechanisms for the photomultiplication processes in organic devices are introduced. Finally, the paper is summarized and the prospects of future research into organic photomultiplication photodetectors are discussed. Full article
(This article belongs to the Special Issue Optoelectronic Nanodevices)
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