Special Issue "Optoelectronic Nanodevices"

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

Deadline for manuscript submissions: 30 November 2018

Special Issue Editor

Guest Editor
Dr. Minas M. Stylianakis

B.Sc, M.Sc Chemistry, Un. Patras (Upatras) PhD, Un. of Crete (UOC) Technological Educational Institute (T.E.I) of Crete, Center of Materials Technology & Photonics Estavromenos P.B 1939, Heraklion, GR-71004, Crete, Greece
Website | E-Mail
Interests: graphene; 2D nanomaterials; materials science; chemistry; 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 (9 papers)

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Research

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
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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
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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
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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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Graphical abstract

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
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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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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Type: Article
Title: Reinforced Field Emission Devices from Reduced Graphene Oxide Ink/Conductive Polymeric Composites
Authors: Minas Stylianakis 1,†,*, George Viskadouros 1, 2,†,*, Christos Polyzoidis 1, George Veisakis 1, Konstantinos Petridis 1,3 and Emmanuel Kymakis1
Affiliation:
1   Center of Materials Technology and Photonics & Electrical Engineering Department, Technological Educational Institute (TEI) of Crete, Heraklion 71004 Crete, Greece; polyzoidis@staff.teicrete.gr (C.P.); gveisakis@staff.teicrete.gr (G.V.); c.petridischania@gmail.com (K.P.); kymakis@staff.teicrete.gr (E.K.)
2   Department of Mineral Resources Engineering, Technical University of Crete, Chania, 731 00, Crete, Greece
3   Department of Electronic Engineering Technological Educational Institute (TEI) of Crete, Chania 73132 Crete, Greece
*   Correspondence: stylianakis@staff.teicrete.gr (M.M.S.); viskadouros@staff.teicrete.gr (G.V.); Tel.: +30-2810-379775 (M.M.S.)
†    These authors contributed equally to this work.
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 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 ratio, FE performance of the composite materials 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 0.6V/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.
Keywords: field emission; graphene; reduced graphene oxide; polymer composites; graphene ink; cold cathode; Fowler-Nordheim

Title: Controllable Synthesis of 2D Perovskite on Different Substrates and Its Application as Photodetector
Author: Shaojuan Li
Abstract: The excellent photovoltaic and photoelectric properties of perovksites have generated growing interest for diverse optoelectronic applications. These applications place extreme demands on device performance that highly depends on the perovskite material properties. However, the widely used spin-coating perovskite compound solution method can only prepare polycrystalline perovskite and physical vapor deposition (PVD) method requires a higher melting point (>350 oC) 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 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 oC. We found that the PL characteristics of perovskite depend strongly on the platelets thickness, namely, thicker peroskite 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 AW-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.

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