KR102651543B1 - Optoelectronic deivce and Smart Window comprising thereof - Google Patents

Abstract

The optoelectronic device and smart window according to the present disclosure include a substrate, an electrode portion including a first electrode and a second electrode provided on the substrate, an active layer provided between the first electrode and the second electrode, and an ionic liquid covering the active layer. Includes.

Description

Optoelectronic device and smart window comprising the same

The present disclosure relates to an optoelectronic device and a smart window including the same.

Reducing energy consumption is becoming a global priority due to the onset of global warming and the potential to reduce device operating costs. Therefore, it becomes important to find low-power device alternatives to current technologies and devices that indirectly reduce energy consumption. This is especially true for many optical applications that require electrical control of optical properties. Because it is difficult to modulate the Fermi-level and charge-carrier density over a wide range, controlling the transmittance of materials in the visible light region remains a major challenge.

Smart windows are one example of such optical applications. For example, buildings can account for 40% of a developed country's total energy use. This is mainly caused by the high costs of heating, ventilation and cooling. One of the most effective ways to reduce these costs is to reduce the amount of energy consumed by windows, most often due to insufficient heat dissipation. Smart windows refer to windows that can change their transmittance under certain conditions, which can be a general solution to the above-mentioned problems. The most attractive smart windows are electrically controlled and can be controlled manually or automatically. This makes it very easy to change the characteristics of Windows to be most efficient at any time of day. However, it is difficult to create a voltage-driven window that is durable, operates at low power, and can produce large, reversible changes. The best performing smart windows are also expensive.

The present disclosure is intended to provide an optoelectronic device and a smart window including the same.

Dynamic electrical control of the optical properties of an active layer having a layer structure according to one disclosure may include an ion liquid gating technique (ILG technique) using low power. The present disclosure can advantageously describe various issues in smart windows, including other low-power optical devices.

To overcome the problems described above, ionic liquid gating techniques are used in several embodiments and can be used to dynamically adjust the optical properties of the active layer. According to various embodiments, the basic architecture may be similar to the MOSFat structure. The basic architecture may include a source electrode and a drain electrode in contact with the active layer, and a gate electrode spaced apart from the rest of the device. An ionic liquid, for example an ionic salt that is liquid at room temperature, can then be applied to the device. Ionic liquids can correspond to oxidized dielectrics in MOSPAT. By changing the voltage applied to the gate electrode, a high density of electrons is applied, and the electrical characteristics of the active layer can be significantly changed. This ionic liquid gating technique applies a small voltage of -3V to 3V in the visible and infrared regions (same voltage as a typical AA battery) to create a window in a very thin nanoplate (several nanometers to tens of nanometers thick). Transmittance can be adjusted. This can be used in any type of application where it is desired to electrically control the absorption, transmission, or reflectance properties of a material for various embodiments.

Compared to using a conventional oxidized dielectric, the electric double layer (EDL) technique according to this embodiment can provide low power operation and much stronger charge density control ability. This makes it possible to significantly change the transmittance with low power consumption. The electric double layer technique according to this embodiment not only provides a powerful method of modulating the physical properties or electric mobility characteristics of materials such as Bi ₂ Se ₃ , but also simplifies the device manufacturing process. An electric double layer can be formed by dropping a few drops of ionic liquid with a pipette (pipette method). Ionic liquids can fail outside their electrochemical operating range, causing irreversible damage. Fortunately, ionic liquids can be modulated up to 50% before damaging voltage.

Electrochromicity is one of the methods to bring about changes in the active layer. Electrochromic is a mature technology and has the advantage of being the current standard for smart windows. Electrochromism also eliminates the need to maintain a constant applied voltage to maintain a specific level of opacity. However, electrochromism uses chemical reactions to effect changes, which can lead to instability and undesirable side effects. In contrast, ionic liquid gating techniques utilize promoting charge carriers and are therefore relatively more stable. Electrochromism is also susceptible to overheating. In contrast, ionic liquids are stable even at high temperatures, so they are less likely to be damaged even when light absorption increases. The ionic liquid gating technique according to this embodiment is also more robust than electrochromism and can cause much greater changes in optical properties for the same voltage change. Additionally, the ionic liquid gating technique according to this embodiment allows the active layer to be used thinner, thereby reducing material consumption, process time, and cost.

Other methods, such as thermochromic or liquid crystal methods, either cannot be controlled electrically or require a lot of voltage and power to change optical characteristics.

Various embodiments using ionic liquid gating techniques can be easily used in applications such as large-area electrically controlled smart windows or wide-operation area optical modulators. Possible commercial applications such as smart windows could include smart watches or cell phones, optical filters, and optoelectronic data storage devices. Other applications could likewise be in the area of privacy mirrors and the aerospace industry.

An optoelectronic device according to an embodiment includes: a substrate;

an electrode unit including a first electrode and a second electrode provided on the substrate;

an active layer provided between the first electrode and the second electrode; and

It includes an ionic liquid covering the active layer.

The active layer may include chalcogenide nanoplates.

The chalcogenide nanoplate may be formed of at least one material selected from Bi2Se3, MoSe2, GaSe, MoS2, WSe2, WS2, Bi2Te3, ZnSe, InSe, In2Se3, and ReS2.

The active layer may be formed of a two-dimensional (2D) layered structure material.

The two-dimensional material having the layered structure may be formed of at least one material selected from the group consisting of Bi ₂ Se ₃ , MoSe 2 , black phosphorus, ZnO, GaAs, Ge, and Si.

The thickness of the active layer may be 20 nanometers or less.

The ionic liquids include DEME][TFSI], [DEME][BF4], [EMIM]-[BF4], [BMIM][BF4], [BMIM][TFSI], [TMPA][BF4], and [DEME][ It may include at least one of [FSI], [EMIM][FSI].

It may further include a power source that is coupled to the electrode unit and modulates optical characteristics of the optoelectronic device.

The power source may modulate the transparency of the optoelectronic device by applying a voltage of -3V to 3V to the electrode unit.

The first electrode may be provided so as not to be electrically connected to the active layer.

The substrate is glass, sapphire, quartz, silicon dioxide, silicon nitride, gallium nitride, plastics, and boron nitride. , ITO, AZO, IZO, FTO, CdO, CdZnO, CdNiO, PEDOT, and graphene.

The electrode unit may further include a third electrode provided on the substrate.

The first electrode functions as a gate electrode that is not electrically connected to the active layer, the second electrode is electrically connected to the active layer and functions as a drain electrode, and the third electrode is electrically connected to the active layer and serves as a source. It can function as an electrode.

The third electrode may be provided on the same plane as the first electrode and the second electrode.

It may further include a protective layer covering the device.

The ionic liquid may be encapsulated by the protective layer.

The ionic liquid may cover the active layer using spin coating or pipette method.

The active layer may have any one of the following shapes: square, circular, triangular, oval, rectangular, hexagonal, or polygonal.

A smart window according to one disclosure includes a plurality of optoelectronic devices according to the above-described embodiments; and

and a power source coupled to the plurality of optoelectronic devices and modulating optical characteristics of the plurality of optoelectronic devices.

The optoelectronic device according to the present disclosure and the smart window including the same can have optical characteristics changed even at a low voltage of -3V to 3V.

The optoelectronic device according to the present disclosure and the smart window including the same include ionic liquid, so the process is simple, the cost is reduced, and optical properties can be greatly changed. In addition, the optoelectronic device according to the present disclosure and the smart window including the same include ionic liquid, can be driven at low power, and have a high ability to control charge carrier density.

The optoelectronic device according to the present disclosure and a smart window including the same may include an active layer. The active layer may include chalcogenide or a two-dimensional material. The optoelectronic device according to the present disclosure and the smart window including the same may be thin and have excellent optical characteristics.

1A to 1D are diagrams of nanoplates and optical devices including nanoplates. Figure 1A is a diagram showing an optical image of Bi2Se3 nanoplates on a glass substrate. Figure 1B is a diagram showing an AFM image of a Bi2Se3 nanoplate. FIG. 1C is a graph showing the thickness of the cross section of the AFM image according to FIG. 1B. Figure 1D is a diagram showing SEM_EDS mapping showing the distribution of Se element in Bi2Se3 nanoplates. Figure 1E is a diagram showing SEM_EDS mapping showing the distribution of Bi elements in Bi2Se3 nanoplates. Figure 1F is a diagram schematically showing the configuration of an optical device using ionic liquid as gate modulation. Referring to Figure 1F, a gate voltage is applied between the gate electrode formed of gold and the Bi2Se3 nanoplate, and the arrow indicates the direction of light propagating to the optical device. The scale bar on the figure represents 10 micrometers.
2A to 2C are diagrams of optical devices including Bi2Se3 nanoplates. Figure 2A is a diagram showing transparency modulation of Bi2Se3 nanoplates using EDLG. Referring to Figure 1, a schematic diagram showing electron accumulation in an EDL transistor is shown. EDL transistors operate using ionic liquid as a gate modulator. The accumulation of charge results in an electric field at the surface, which can be used to modulate the charge density of the surface-charge-accumulation layer on the surface of the Bi2Se3 sample. FIG. 2B is a graph showing the optical transmission spectrum of Bi2Se3 nanoplates in the 400-900 nm region under the application of an EDL gate voltage. Referring to Figure 2B, in the optical transmission spectrum, the transmittance in the long wavelength region is higher than the transmittance in the short wavelength region. The spectrum describes the widening and narrowing of the optical band gap when a positive and negative voltage is applied to the EDL gate voltage. Figure 2C is a diagram showing an optical transmission image of a 15 nm thick Bi2Se3 nanoplate when an EDL gate voltage is applied. Referring to Figure 2C, the optical modulation pattern of the Bi2Se3 nanoplate according to the application of the EDL gate voltage can be clearly confirmed.
3A to 3C are diagrams showing the transmittance and reflectance of Bi2Se3 in the infrared region under an EDL gate voltage. Figure 3A is a diagram showing the optical transmission spectrum of Bi2Se3 nanoplates under EDL gating modulation. Figure 3B is a diagram showing the optical reflection spectrum of Bi2Se3 nanoplates under EDL gating modulation. Due to the simultaneous modulation of the electronic plasma edge and absorption edge of the nanoplate by applying the EDL gate voltage, the modulation spectrum in the near-infrared region shows the range of modifiable reflection wavelengths. Figure 3C shows the positive wavelength range, based on density functional theory calculations. It shows the band structure of the Bi2Se3 nanoplate to which voltage was applied (top), the band structure of the Bi2Se3 nanoplate to which no voltage was applied (middle), and the band structure of the Bi2Se3 nanoplate to which a negative voltage was applied. The dashed line indicates the location of the Fermi level.
Figures 4A-4D show the optical properties of Bi2Se3 nanoplates as a function of ionic liquid gate voltage. Figure 4A shows the transmittance values of Bi2Se3 nanoplates as a function of ionic liquid gate voltage at a long wavelength of 3.5 micrometers and a short wavelength of 1.5 micrometers. Figure 4B shows the reflectance values of Bi2Se3 nanoplates as a function of ionic liquid gate voltage at a long wavelength of 3.5 micrometers and a short wavelength of 1.5 micrometers. Figure 4C shows plasma frequencies extracted from experimental results based on the Drude Model. Figure 4D shows the experimentally measured onsets of absorption (maximum transmission) and calculated direct optical transition energies near the Fermi level (effective bandgap) as a function of the ionic liquid gate voltage. Referring to Figure 4D, the hollow circles represent experimentally measured absorption onsets and the solid circles represent calculated direct optical transition energies near the Fermi level. The increase in effective bandgap is consistent with the experimental observation that the maximum transmission wavelength shifts to a shorter wavelength.
Figures 5A to 5C show MoSe ₂ under EDL gating. Indicates the infrared transmittance of . Figure 5A shows MoSe ₂ under EDL gating modulation. This is a diagram showing the optical transmission spectrum of the flake. Figure 5B shows MoSe ₂ under EDL gating modulation. This diagram shows the optical reflection spectrum of the flake. Due to the simultaneous modulation of the electronic plasma edge and absorption edge of the nanoplate by applying the EDL gate voltage, the modulation spectrum in the near-infrared region shows a modifiable reflection wavelength region. Figure 5C shows MoSe ₂ with positive voltage applied, based on density functional theory calculations. Showing the band structure of the flake (top), MoSe ₂ without voltage applied. Shows the band structure of the flake (center) and MoSe ₂ with applied negative voltage. Shows the band structure of the flake. The dashed line indicates the location of the Fermi level.
Figures 6A and 6B are plots showing changes in charge state as evidenced by transport measurements. Figure 6A is a diagram showing the transport characteristics (I _DS -V _G ) of Bi2Se3 nanoplates under EDL gate voltage. Figure 6B shows MoSe ₂ under EDL gate voltage. This is a diagram showing the transport characteristics (I _DS -V _G ) of flakes. MoSe ₂ Compared to flakes, the charge transport properties are similar to those of Bi2Se3 nanoplates heavily doped with n-type dopant - the Fermi level does not enter the valence band. The arrow indicates the direction of continuous change in the applied voltage.
Figures 7A and 7B are diagrams showing AFM images of Bi2Se3 nanoplates. The left images of Figures 7A and 7B are AFM images of a nanoplate with a thickness of 12 nm and a nanoplate with a thickness of 22 nm. The right images of FIGS. 7A and 7B are graphs showing the cross-sectional thickness of a nanoplate with a thickness of 12 nm and a nanoplate with a thickness of 22 nm.
Figures 8A and 8B are graphs showing Raman spectra. Figure 8A is a graph showing the Raman spectrum of the FQLs Bi2Se3 nanoplate in the 10-450 cm ^-1 region. Figure 8A is a graph showing the Raman spectrum of FQLs MoSe ₂ in the 10-450 cm ^-1 region. Referring to the drawing, it can be seen that the peak positions of the Raman spectra of Bi2Se3 nanoplates are consistent with each other, and that two-dimensional materials with different layer structures are also consistent with each other.
Figures 9A and 9B are diagrams showing electron diffraction patterns and TEM images of Bi2Se3 nanoplates.
Figure 10A shows the transmission spectrum of Bi2Se3 nanoplates as the ionic liquid gating voltage increases from negative to positive values. The result has a similar form to that described previously and shows an absorption edge in the short wavelength band and a plasma edge in the long wavelength band. Figure 10B shows the change in transmittance characteristics according to the gate voltage at short wavelength (1.5um) and long wavelength (3.5um).
Figures 11A and 11B show reflectance spectra of MoSe2 flakes upon applying positive and negative ionic liquid gating voltages, respectively. The modulation spectrum in the near-infrared region appears similar to that of layered Bi2Se3 nanoplates.
Figures 12A and 12B are diagrams showing the transport characteristics (I _DS -V _G ) of Bi2Se3 nanoplates. Figure 12A is a diagram showing the transport characteristics (I _DS -V _G ) of Bi2Se3 nanoplates using the ([DEME]-[TFSI]) ionic liquid gate effect. Figure 12B is a diagram showing the transport characteristics (I _DS -V _G ) of Bi2Se3 nanoplates using the ([EMIM]-[BF4]) ionic liquid gate effect.
13A to 13D are diagrams showing a device manufacturing process. Figure 13A shows steps for preparing Bi2Se3 nanoplates on a glass substrate. Figure 13B is a diagram showing the outlines of the gate, source, and drain after performing photolithography processing steps. Figure 13C is a diagram showing the outline of the device after performing a photolithography process on a Bi ₂ Se- ₃ nanoplate. Figure 13D is a diagram showing the step of forming a gold electrode on a Bi ₂ Se- ₃ nanoplate. The device according to this embodiment may have a width of 50 micrometers and a width of 30 micrometers.
14 is a schematic plan view of an optoelectronic device according to one embodiment.
FIG. 15 is a schematic cross-sectional view of the optoelectronic device according to FIG. 14 taken along line A-A'.
FIG. 16 is a cross-sectional view schematically showing the application of voltage to the first electrode of the optoelectronic device according to FIG. 14.
FIG. 17 is a cross-sectional view schematically showing the application of voltage to the first electrode of the optoelectronic device according to FIG. 14.
18 is a schematic plan view of an optoelectronic device according to another embodiment.
FIG. 19 is a schematic cross-sectional view of the optoelectronic device according to FIG. 18 taken along line B-B'.
FIG. 20 is a schematic cross-sectional view of the optoelectronic device according to FIG. 18 taken along line C-C'.
Figure 21 is a schematic plan view of a smart window according to one embodiment.

Hereinafter, the optoelectronic device and smart window will be described in detail with reference to the attached drawings. The width and thickness of layers or regions shown in the attached drawings may be somewhat exaggerated for clarity and convenience of description. Like reference numerals refer to like elements throughout the detailed description.

The terminology used in the present disclosure selects general terms that are currently widely used as much as possible while considering the functions of the components in the embodiments, but this may vary depending on the intention or precedent of a technician working in the art, the emergence of new technology, etc. . In addition, in certain cases, there are terms arbitrarily selected by the applicant, and in this case, the meaning will be described in detail in the description of the relevant embodiment. Therefore, the terms used in this embodiment should be defined based on the meaning of the term and the overall content of this embodiment, rather than simply the name of the term.

Terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. Terms are used only to distinguish one component from another.

Singular expressions include plural expressions unless the context clearly dictates otherwise. Additionally, when a part "includes" a certain component, this means that it may further include other components rather than excluding other components, unless specifically stated to the contrary.

The emergence of 2D layered structural materials prior to graphene has brought new horizons to the exploration of low-dimensional electrical systems. Two-dimensional materials with such a layered structure, such as hexagonal boron nitride (h-BN) or transition metal dichalcogenides (TMDCs), have weak van der Waals forces between multiple layers and strong interlayers. Can be formed by covalent bonds. The diverse spectral properties of layered two-dimensional material crystals could enable potential applications in transparent electrodes, sensing, nonlinear optics, and vellytronics. It has been shown that bismuth selenide (Bi ₂ Se ₃ ), a type of two-dimensional material with a layered structure, can function as a topological insulator (TI). This is a result of the unbroken time-reversal symmetry of bismuth selenide, which can be characterized by a gapless linear energy dispersion relationship at the sample boundary and a band-insulating property in the bulk. Recently, several research groups have shown that the electro-optical properties of bismuth selenide can be tuned by bulk doping, intercalation layers, and surface accumulation. The large changes in the optical properties of bismuth selenide have raised special interest in this material system. However, such processes must be completed at the material preparation stage, and the optical properties of the material cannot be changed once the optical device is completed. Dynamic electrical control of the optical properties of layered dichalcogenides has not yet been reported. This is due to the difficulty in controlling the Fermi level and carrier density of chalcogenides in a wide area using traditional electrical gating approaches.

To overcome these problems, according to various embodiments, an electric-double layer (EDL) gating technique at room temperature is used to dynamically adjust the optical properties of layered two-dimensional materials from the infrared region to the visible wavelength region. can be used for Dynamic optical modulation induced by EDL gating can also be used in applications that are not suitable for embedded layer techniques, such as wide-wavelength optical modulators and large-area electrically controlled smart windows. Because the gating technique is electrically controlled, these devices can be easily controlled using optical sensors and batteries. Here, a two-dimensional material with a layered structure refers to a material that can naturally form a two-dimensional structure with a layered structure or a material that can form a very thin layered structure of a few nanometers to dozens of nanometers. For example, two-dimensional materials with a layered structure may include bismuth selenide, molybdenum selenide, and even Si.

EDL gating uses an ionic liquid (IL) as a gate dielectric to efficiently control the electrical state and adjust the Fermi energy (E _F ) of the semiconductor over a wide range. Compared to the use of conventional oxide dielectrics, the EDL gating technique can provide low power, high mobility, fast switching, and large charge carrier density control. When a gate voltage (V _G ) is applied to the electrode, an electric double layer (EDL) is created at the liquid/solid (L/S) interface after rearrangement of ions, creating a large capacitance due to the nanogap capacitor. You can make it. The capacitance of the electric double layer is 10 μF/cm ² This means that under the same gate voltage (V _G ), more charge carriers can be accumulated or depleted on the surface of the sample more effectively than a FET containing a conventional oxidized dielectric. do. These advances can lead to improved electrical modulation of the electrical state of the contact surface. For example, ZrNCl and SrTiO ₃ It can have electrostatically induced superconductivity. The unexpected gating ability of ionic liquids can lead to a dynamic increase in optical transparency changes through bismuth selenide nanoplates by applying negative or positive voltages to the gate voltage. Detailed aspects of this will be described later. Similar dynamic control of optical changes can also be observed with other layered TMDC materials, such as MoSe ₂ . Lowly doped MoSe ₂ , in contrast to bismuth selenide, shows optical tuning properties independent of the sign of the gate voltage, which are in good agreement with its own ambipolar electrical properties. Ionic liquid gating techniques are not only a powerful way to modulate the electrical transport and other physical properties of materials such as bismuth selenide, but can also reduce energy consumption and simplify the process. The EDL gating technique, based on ion transport and EDL formation, allows the gate electrode to be moved away from the gate material, completely eliminating the metal gate structure formed on the material, which blocks light in conventional gate structures. This provides advantages in optical measurements and optical device design.

[Material preparation and properties]

According to some embodiments, 2D nanoplates may be synthesized using solvothermal synthesis techniques. For example, in one embodiment, bismuth selenide nanoplates can be synthesized solvothermically. The thickness of nanoplates can range from a few nanometers to tens of nanometers. The horizontal dimension of the nanoplates can reach 80 micrometers or even larger, which is larger than other reported materials using solvothermal synthesis and can provide a good platform for optical studies. A typical optical image of bismuth selenide nanoplates prepared on a glass substrate is shown in Figure 1A. Referring to Figure 1A, the horizontal size of the bismuth selenide nanoplate is about 50 micrometers. The thickness of bismuth selenide nanoplates can be imaged by AFM, which is shown in Figure 1B. Figure 1C shows a thickness graph along the horizontal direction of the nanoplate according to Figure 1B, and the thickness of the nanoplate is approximately 11 nanometers. Examples having different thicknesses of nanoplates will be described later with reference to FIG. 7 . Raman spectroscopy can be used to confirm the uniformity of nanoplate growth, which is shown in FIG. 8. Referring to Figure 8, three distinct characteristic peaks are observed at 71 cm ^{- 1} , 131cm ^{- 1} , It is confirmed at 173 cm ^-1 , which matches very well with the previously reported Raman spectrum of bismuth selenide. [Reference Zhang, J., et al. Raman Spectroscopy of Few-Quintuple Layer Topological Insulator Bi2Se3 Nanoplatelets. Nano Lett 11, 2407-2414 (2011).]. To better identify the components of the bismuth selenide nanoplates, the bismuth selenide nanoplates can be mapped using scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDS), and the results are shown in Figures 1D and 1E. is shown in Electron diffraction results are shown in Figure 9B and indicate the single crystalline nature of the nanoplates.

Optical modulation of bismuth selinide nanoplates controlled by EDL gating was shown, and optical spectra were measured to compare the properties of individual nanoplates with and without ionic liquid gating. Figure 1F shows the arrangement of a device using EDL for gate modulation according to an embodiment. A voltage may be applied between the bismuth selenide nanoplate and the gold gate electrode. The cover glass can uniformize the thickness of the EDL, reducing lens effects and effects due to liquid movement after processing. The arrow indicates the direction of light propagating through the device. The ionic liquid according to this embodiment may be N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis-(trifluoromethylsulfonyl)-imide ([DEME]-[TFSI]). [DEME]-[TFSI] is an imidazolium-based compound that has high ionic conductivity and is widely used in EDL devices. [DEME]-[TFSI] can have a very wide transparent wavelength range from visible light to the mid-infrared region and can completely cover the frequency range of interest. A drop of ionic liquid can be placed on both a gold electrode and a bismuth selenide nanoplate, and the electrodes can be attached to form a gold/ion liquid/bismuth selenide/gold arrangement, as shown in Figure 1F. The size between the source and electrode of the device may be width W=50μm and length L=30μm. It should be understood that the size of the device may change. For example, the length of the device can vary from 100 nanometers to a meter, and the width can vary from tens of nanometers to a meter. The device can be covered by ionic liquid droplets.

EDL gating causes the optical response of bismuth selenide even in the visible frequency range. Figure 2B is a diagram showing the transmission spectrum of bismuth selenide with and without EDL gating in the wavelength range of 400-900 nm. When no gate voltage is applied, the optical transparency of the device may be relatively low, for example on the order of 40%. On the contrary, if a positive voltage is applied to the gate voltage, the transmittance in all visible wavelength ranges can be greatly improved. For example, when a gate voltage of 1.5V is applied, the transmittance can increase to 70% in most areas of visible light, which means that the bismuth selenide nanoplates have become more transparent. On the other hand, when applying a negative gate voltage, the bismuth selenide nanoplates may become more opaque. When a gate voltage of -1.5 V is applied, the transmittance can be reduced to about 20% in most areas of visible light. Figure 2C shows optical transparency images of bismuth selenide nanoplates with ionic liquid gating applied when the thickness of the bismuth selenide nanoplates is about 15 nm. According to the results shown, the optical modulation properties of bismuth selenide nanoplates by ionic liquid gating are clearly demonstrated. Furthermore, referring to Figure 2B, as the wavelength becomes longer, the transmittance improves. This trend continues into the region adjacent to the infrared wavelengths, providing clear evidence of an absorption edge. Below, we introduce experimental evidence to explain the mechanism of the rapid optical modulation properties of bimetallic chalcogenide nanoplates using EDL gating.

According to an advantageous aspect according to various embodiments, the free carriers induced by EDL gating can modify the conductivity of the material and their optical properties can also change significantly. According to Figures 3A and 3B, the transmission spectrum and reflection spectrum of bismuth selenide nanoplates under EDL gating in the near-infrared region are shown. In the optical spectrum, the short wavelength ( ie λ<2.5μm) absorption edge cut-off corresponds to the optical gap of the bismuth selenide nanoplates, and the long wavelength ( ie λ>2.5μm) edge corresponds to the plasma resonance frequency of the free carriers. . To better interpret the experimental results, the transmittance and reflectance values are shown in Figures 4A and 4B. Referring to Figures 4A and 4B, the wavelength λ=1.5μm where the transmittance value and reflectance value are fixed. and λ=3.5μm is plotted as a function of EDL voltage. Referring to Figures 4A and 4B, the optical transmittance and reflectance values are strongly dependent on the EDL voltage. Additionally, the graph also shows the contrasting aspects of short and long wavelengths. For example, the transmittance increases when the EDL voltage is increased at a short wavelength λ = 1.5 μm, but the transmittance value decreases when the EDL voltage is increased at a long wavelength λ = 3.5 μm, which is caused by two optical processes by EDL gating modulation. Indicates that there is. That is, the variable that controls the transmittance value may include two factors: EDL gating voltage and wavelength length.

This tendency can be explained by the Drud model. The Drude model creates a direct link between the optical response of conducting materials and their electrical state. According to the Drude model, the modulated relative permittivity ε can be described by the following equation.

… Equation 1

where ε _∞ is the high-frequency dielectric constant, is the attenuation constant of free electron plasma, and τ represents the excitation time of electrons. The plasma resonance frequency is It is described as Here, N represents the free carrier density, m* represents the effective mass of electrons, and n and k represent optical constants that determine the reflection and absorption spectra of the material, respectively.

The Drude model according to Equation 1 can be considered in two limited cases: a case where the frequency is low and a case where the frequency is high. low frequency range ( ), in Equation 1 According to the free carrier The dependence of the term increases, which means that in the low frequency range this term is the dominant term, and at low frequencies it can function as a perfect reflector. However, in the high frequency region ( ) of the free carrier contribution. As the contribution of the term decreases, other mechanisms may become more important. Therefore, in the high frequency region ( ), the free carrier contribution can be neglected and the material behaves like a dielectric.

This example case ( ), free carriers play an important role in the optical properties of bismuth selenide. Plasma frequency is the characteristic frequency at which a material changes from a metal to a dielectric optical response, and occurs at a frequency where the real part of the relative transmittance disappears ( ). Plasma frequency ( ) depends on the free carrier concentration and inversely on the effective mass of the effective carriers. The plasma edge of a material refers to the area near the plasma frequency, and the reflectivity increases rapidly as the incident wavelength increases. The Drude model shows that the plasma edge is shifted to the shorter wavelength region due to positive EDL modulation of the free carrier density.

As shown in Figures 3A-3C, the reflection and transmission spectra show a significant short-wavelength shift of the plasma edge induced by positive EDL modulation. This behavior provides direct evidence that the amount of free electrons increases inside the material induced by EDL, which is consistent with the content of the Drude model described above. The Drude model was applied to the measured results, and the value of the plasma frequency was obtained in good agreement with the long-wavelength experimental results shown in FIG. 10. Plasma frequency values can be obtained from mathematical fitting of each curve. Referring to FIG. 4, the plasma frequency depends nonlinearly on the EDL voltage due to changes in effective mass and free electron density due to the evolution of the Fermi level of the bismuth selenide nanoplate. for example, When applied, the plasma frequency is , and with fitting parameters etc. can be applied. The corresponding electron carrier density can be calculated from the plasma frequency, resulting in a very high free electron concentration of 10 ²⁰ cm ^-3 . This level of electron concentration modulation may be the greatest benefit of using EDL gating with layered two-dimensional materials. Referring to Figure 11, in order to study the dynamic optical response of bismuth selenide nanoplates under EDL modulation, the relative transmittance of bismuth selenide under an applied EDL voltage is calculated. When the plasma frequency is raised, the imaginary part of the transmittance becomes very large. This is predicted by the Drood model when carrier densities are very high. This confirms that the amount of free electrons induced by EDL increases inside the material.

A secondary effect of free carrier density modulation is a significant shift of the absorption edge. The absorption edge originates from the onset of the optical transition beyond the fundamental bandgap of the material, which is evident at short wavelengths as a result of the significant increase in transmission with increasing incident wavelength. The optical modulation behavior of bismuth selenide nanoplates from the visible to the infrared band is mainly caused by the significantly changing effective optical bandgap, which may be a result of the large free electron density modulation of bismuth selenide nanoplates through EDL gating. there is. This effect is known as Burstein-Moss shift. As the electron density increases, the Fermi level of the material rises to enter the conduction band, and empty states at the band edges can become invalid. Therefore, the optical transition to the bottom of the conductive band is less pronounced, which may result in an increase in the effective bandgap.

For a quantitative study of the correlation between EDL voltage and Fermi level shift, the electronic structure of bismuth selenide is calculated by density functional theory (DFT). Under the assumption that the EDL gating voltage does not significantly change the density of states (DOS) near the minimum of the conduction band, we calculated the Fermi level experimentally from the induced carrier density. As shown in Figure 3C, as the EDL gating voltage changes from -1.5 V to 1.5 V, the Fermi level energy is predicted to increase by 0.34 V. When the EDL gating voltage is not applied, the Fermi level is located inside the conduction band, which is due to the n-type dopant-doped nature of the bismuth selenide nanoplate (see middle diagram of Figure 3C). When a positive voltage is applied to the EDL gating, more electrons accumulate on the surface of the bismuth selenide nanoplate, and a blue shift of the absorption region occurs as the effective band gap increases. The negative voltage applied to the EDL gating can lower the Fermi level through a decrease in free carrier concentration, shift the absorption edge to lower energy, and enable optical transition at lower energy. This is as shown in the experimental spectra in the near-infrared region of Figures 3a and 3b, and can provide a direct basis for the optical modulation pattern observed in the experiment. The number of lines depending on the change in band structure may be due to subband formation. However, according to previous research results, the change in band structure due to subband formation is too small to affect optical measurements (Yao et al). The measured absorption starting point as a function of gate voltage is shown in Figure 4d. The blue shift at the transmittance maximum is consistent with the increase in effective bandgap derived from free electron carrier calculations.

To better characterize the EDL technique, similar gating experiments were performed using other transition metal dichalcogenide materials, such as MoSe ₂ . Dynamic tuning of optical properties was achieved by applying similar gating voltages to MoSe ₂ The same is observed in flakes. Figures 5a and 5b show MoSe ₂ near the infrared region when positive and negative gate voltages are applied, respectively. The modulated transmittance spectrum of flakes (thickness less than 30 nm) is shown. Referring to Figure 5C, unlike bismuth selenide nanoplates, MoSe ₂ The Burstein-Moss shift in the multilayer structure occurs for both holes (valence band) and electrons (conductivity band). Referring to Figure 5c, the Fermi level is MoSe ₂ lightly doped with n-type dopant. It can be located in the bandgap of the flake (middle part of Figure 5c). Additionally, when a positive gate voltage is applied, the Fermi level is located in the conduction band (top of Figure 5c). On the other hand, when a negative gate voltage is applied, holes are transferred to MoSe ₂ accumulates in flakes. In this case, the Fermi level can lie in the valence band (VB) (bottom of Figure 5c). The increased free electron density induced by EDL gating results in a shift of the Fermi level into the conduction band. The increased free hole density induced by EDL gating results in a shift of the Fermi level into the valence band. In both cases, the effective band gaps are both raised, which contrasts with the behavior of bismuth selenide. Gating induces changes in optical changes associated with Burstein-Moss shifts in both the conduction band and the valence band, which exhibit symmetric ambipolar behavior. The observed results indicate that EDL gating can be used to increase the free carrier density of layered two-dimensional material systems to very large values without any chemical reaction. Due to the simultaneous movement of the electron plasma edge at long wavelengths and the absorption edge at short wavelengths under the condition of applied EDL gate voltage, both bismuth selenide and MoSe ₂ exhibit tunable optical properties with a tunable transparent spectral window from the infrared to the visible region. indicates. Compared to general chemical doping, EDL gating produces a larger shift in the Fermi level, and this technique produces strong optical modulation over a wider wavelength range, which can include the visible wavelength range, enabling modulation of optical properties. It can be used in applications that require it. Such behavior can also occur using other ionic liquids.

As shown in FIG. 6A, the change in electrical state that causes the optical effect described above can be confirmed through transport characteristics. For example, the gate voltage can appear as a function of source-drain current when EDL gating is applied to a bismuth selenide device at room temperature. As the gate voltage is increased, positive ions are induced on the top of the thin film, and a large amount of electrons are induced on the bismuth selenide surface, thereby increasing the intensity of the source-drain current with an increase in electronic conductivity (see Figure 6a). ). Relatively, when a negative gate voltage is applied, electrons are depleted from the surface of the nanoplate, which may mean that the intensity of the source-drain current decreases as the electron concentration decreases. The charge accumulation creates an electric field at the surface, which can be used to modulate the Fermi level or the electron density of the surface-electron-accumulation layer at the surface of the bismuth selenide sample. Figure 6B shows MoSe ₂ under applied EDL gating voltage at room temperature. The transport properties of the flakes are shown. The bipolar properties observed at room temperature are due to MoSe ₂ lightly doped with n-type dopant. Consistent with the characteristics of flakes. Referring to Figure 12, each sample was measured to have similar transmission characteristics, which indicates high reproducibility.

As far as dynamic optical modulation of very thin bismuth selenide nanoplates is concerned, very large dynamic changes in transmittance and reflectance can be achieved when the nanoplates are as thin as 10 nm or less. This rapid optical change may be due to expansion of the effective optical bandgap due to modulation of the Fermi energy and electrical state of the bismuth selenide sample using EDL gating. Changes in dynamic optical properties were also confirmed in MoSe ₂ , a two-dimensional material with a similar layer structure. The subtle differences in the gating voltage dependence between them are consistent with the differences in the location of the Fermi level in the two materials. Simultaneous modulation of the plasma edge and absorption edge could enable potential applications as electrically controllable smart windows or optical modulators in a wide spectral range. The two-gate EDL-FET structure can be used to improve switching speed in a very small regulation region.

[Example methods]

[ selenization of bismuth nanoplates Solvothermal Fusion Department device process]

Dynamic bismuth selenide nanoplates can be prepared via solvothermal fusion. [Reference eg, Kong, DS, Koski, KJ, Cha, JJ, Hong, SS & Cui, Y. Ambipolar Field Effect in Sb-Doped Bi2Se3 Nanoplates by Solvothermal Synthesis. Nano Lett 13, 632-636 (2013).] Metal-based selenium powder and metal-based Bi ₂ O ₃ Dissolve the powder in ethyl glycol. Afterwards, EDTA powder and pure PVP are added. Next, the sample is sonicated and sealed in an autoclave (pressure processor). As a result, the autoclave is baked in an oven at 200°C for about 24 hours, and then gradually cooled down to room temperature. It goes through a filtering process and ethanol washing process several times. Then, it is dried in a vacuum at 90°C. To suspend the resulting black powder, it is prepared on a glass substrate using a pipette. The average thickness and horizontal size of the nanoplates can be optimized by modifying the EDTA concentration and temperature. MoSe ₂ flakes with a multilayer structure can be prepared by a mechanical exfoliation process. Electrical devices can be made by patterning electrodes through optical lithography processes. The nanoplates can be reactive ion etched to leave no organic residues or surface oxides. EBM (E-beam evaporation) can be used to form the source electrode, drain electrode, and gate electrode using Cr/Au at 5nm/100nm conditions. As a result, the sample can be attached to a chip holder using wire bonding. The device process is as shown in FIG. 13. The thickness of the nanoplate can be measured by AFM, and for hexagonal samples, the thickness can range from 8 nm to 22 nm. The chemical properties of the bismuth selenide nanoplates and the quality of the plurality of MoSe ₂ flakes can be confirmed by Raman spectra, as shown in FIG. 8. The crystallinity of bismuth selenide nanoplates can be confirmed by checking the transmittance using an electron microscope technique, as shown in FIG. 9.

[Optical Transmission, reflection and electrical transmission measurements]

Bismuth selenide nanoplates can be formed by drop casting on a glass substrate. All electrical property measurements can be performed at a conventional probe station under air conditions at room temperature. AFM measurements can be performed to measure the thickness of the bismuth selenide nanoplates and the plurality of MoSe ₂ flakes prior to electrical measurements. Transmittance optical images and visible light spectrum measured under EDL gating voltage were taken with a Nikon Eclipse CI-L or Nikon confocal C1 microscope, respectively. Voltage was applied by a source meter (Keithley-2400). Reflectance and transmittance spectra in the near-infrared region were measured with a Bruker Hyperion 2000 and IFS-125/HR Fourier transform infrared spectrometer at room temperature. A transparent knife-edge aperture was used to adjust the beam size, and all measured transmittance and reflectance light was measured on the nanoplate sample and not near the substrate. All infrared reflectance and transmittance results were normalized to the reflectance of pure gold and the transmittance of a thin glass substrate.

[Substance polymerization and device process]

Bismuth selenide single crystals can be produced by a solvothermal fusion process, and the detailed process is as described above. Other multilayer flake structures can be produced by mechanical exfoliation processes. The experiment was conducted on a nanomaterial structure forming a layered structure. The device manufacturing process may be performed using conventional optical lithography or EBM technique processes. These processes can have micrometer-level precision. The thickness of multiple samples can be measured optically or AFM. Device configurations of flakes or bismuth selenide nanoplates formed from different types of layers are typically 50 micrometers wide and can be 30 micrometers long. Reactive ion etching may be performed prior to formation of the gold electrode. The electrode is formed by an EBM process, and the pattern can be formed by a photolithography process.

Figure 7 shows an AFM image of bismuth selenide nanoplates. The left images of Figures 7A and 7B are AFM images of a nanoplate with a thickness of 12 nm and a nanoplate with a thickness of 22 nm. The right images of FIGS. 7A and 7B are graphs showing the cross-sectional thickness of a nanoplate with a thickness of 12 nm and a nanoplate with a thickness of 22 nm.

[Identification of materials using Raman spectrum]

Materials related to two-dimensional materials with a layered structure were measured using a micro Raman spectrometer, which examines scattering characteristics with a laser wavelength of 473 nanometers. A typical Raman spectrum consisting of several maxima is shown in Figure 8, which matches well with the maximum position of the Raman spectrum of layered structures formed of bismuth selenide nanoplates and other two-dimensional materials with layered structures.

Figures 8A and 8B are graphs showing Raman spectra. Figure 8A is a graph showing the Raman spectrum of the FQLs Bi2Se3 nanoplate in the 10-450 cm ^-1 region. Figure 8B is a graph showing the Raman spectrum of FQLs MoSe ₂ in the 10-450 cm ^-1 region. The positions of the maximum correspond to known Raman spectra of Bi2Se3 nanoplates and other two-dimensional materials with layered structures.

[ selenization Characteristics of the crystal structure of bismuth nanoplates]

To confirm the crystallinity of bismuth selenide nanoplates, transmission electron microscopy can be performed. Referring to Figure 9A, a low magnification TEM image of bismuth selenide nanoplates is shown. Referring to Figure 9b, the single crystal properties of bismuth selenide nanoplates are shown.

[Consistent results involving multiple devices]

To confirm that the optical modulation characteristics in bismuth selenide nanoplates with ionic liquid gating were consistent across multiple devices, a second device of similar size was used in which the ionic liquid was replaced by [EMIM]-[BF4]. Similar optical transmission modulation characteristics are observed as in Figure 10a. In this way, the optical modulation of the second device using the new ionic liquid shows that it has almost similar optical characteristics to the device previously used as [DEME]-[TFSI]. A slight difference is that the absorption maximum occurs in the wavelength region of 2.7-3.3 μm, which is characteristic of the new ionic liquid. Referring to Figure 10b, the relationship between the transmittance and ionic liquid gating voltage at two wavelengths (λ = 1.5 μm and λ = 3.5 μm) of a device using [EMIM]-[BF4] ionic liquid is shown.

Figure 12A is a diagram showing the transport characteristics (I _DS -V _G ) of Bi2Se3 nanoplates using the ([DEME]-[TFSI]) ionic liquid gating effect. Figure 12B is a diagram showing the transport characteristics (IDS-VG) of Bi2Se3 nanoplates using the ([EMIM]-[BF4]) ionic liquid gating effect.

Figure 10A shows the transmission spectrum of Bi2Se3 nanoplates as the ionic liquid gating voltage increases from negative to positive values. The result has a similar form to that described previously and shows an absorption edge in the short wavelength band and a plasma edge in the long wavelength band. Figure 10B shows the change in transmittance characteristics according to the gate voltage at short wavelength (1.5 μm) and long wavelength (3.5 μm).

Figures 11A and 11B show reflectance spectra of MoSe2 flakes upon applying positive and negative ionic liquid gating voltages, respectively. The modulation spectrum in the near-infrared region appears similar to that of layered Bi2Se3 nanoplates.

Figure 12A is a diagram showing the transport characteristics (I _DS -V _G ) of Bi2Se3 nanoplates using the ([DEME]-[TFSI]) ionic liquid gate effect. Figure 12B is a diagram showing the transport characteristics (I _DS -V _G ) of Bi2Se3 nanoplates using the ([EMIM]-[BF4]) ionic liquid gate effect.

[Example Examples ]

[Optoelectronic device work Example ]

14 to 17 describe content related to the optoelectronic device 100 according to an embodiment.

Figure 14 is a schematic plan view of an optoelectronic device 100 according to one embodiment. FIG. 15 is a schematic cross-sectional view of the optoelectronic device 100 according to FIG. 14 taken along line A-A'. FIG. 16 is a cross-sectional view schematically showing a positive voltage applied to the first electrode 121 of the optoelectronic device 100 according to FIG. 14. FIG. 17 is a cross-sectional view schematically showing a negative voltage applied to the first electrode 121 of the optoelectronic device 100 according to FIG. 14.

Referring to FIG. 14 , the optoelectronic device 100 may include a substrate 110, an electrode unit 120, an active layer 130, an ionic liquid 140, and a power source 150.

The substrate 110 may be formed of a material that is transparent or translucent to light in the visible and infrared regions. For example, the substrate 110 is made of glass, sapphire, quartz, silicon dioxide, silicon nitride, gallium nitride, plastics, It may be formed of at least one material selected from boron nitride, ITO, AZO, IZO, FTO, CdO, CdZnO, CdNiO, PEDOT, and graphene.

The electrode unit 120 may include a first electrode 121 and a second electrode 122. The first electrode 121 and the second electrode 122 may be provided to be spaced apart from each other. The first electrode 121 and the second electrode 122 may be connected to the power source 150 to apply voltage. The first electrode 121 and the second electrode 122 may be provided on the same plane on the substrate 110.

The active layer 130 may be provided between the first electrode 121 and the second electrode 122. The first electrode 121 may be provided to be spaced apart from the active layer 130 by a predetermined distance so as not to be electrically connected to the active layer 130 . The second electrode 122 may be in contact with the active layer 130 to be electrically connected to the active layer 130. When looking down at the optoelectronic device 100 in a vertical direction, the active layer 130 may not be obscured by the electrode portion 120. Because of this, light passing through the active layer 130 can be prevented from being scattered by the electrode unit 120.

The active layer 130 may include chalcogenide nanoplates. Chalcogenide nanoplates can be formed of at least one material selected from the group consisting of Bi ₂ Se ₃ , MoSe ₂ , GaSe, MoS ₂ , WSe ₂ , WS ₂ , Bi ₂ Te ₃ , ZnSe, InSe, In ₂ Se ₃ and ReS ₂ there is. The optical modulation characteristics and modulation patterns of the optoelectronic device 100 when the active layer 130 includes bismuth selenide nanoplates (Bi ₂ Se ₃ ) have already been described in FIGS. 2A to 2C, 3A to 3C, and 4A to 4D. Since it is the same as before, detailed information will be omitted. The optical modulation characteristics and modulation patterns of the optoelectronic device 100 when the active layer 130 includes molybdenum selenide (MoSe ₂ ) are the same as those described above in FIGS. 4A to 4D and 5A to 5C, so detailed information is omitted. do.

The active layer 130 may be formed of a two-dimensional material with a layered structure. The two-dimensional material may be formed of at least one material selected from black phosphorus, ZnO, GaAs, and Ge.

The active layer 130 may have one of the following shapes: square, circular, triangular, oval, rectangular, hexagonal, or polygonal. The shape of the active layer 130 may be determined differently depending on the exterior design of the optoelectronic device 100 and is not limited to a specific embodiment.

Ionic liquid 140 may cover the active layer 130. Ionic liquid 140 is [DEME][TFSI], [DEME][BF4], [EMIM]-[BF4], [BMIM][BF4], [BMIM][TFSI], [TMPA][BF4], [ It may include at least one of DEME][FSI] and [EMIM][FSI]. The ionic liquid 140 functions as a kind of gate dielectric, operates at low power compared to a conventional oxidized dielectric, and allows the density of charge carriers to be controlled within a large range. When the gate voltage is applied to the first electrode 121, charges are induced at the solid/liquid interface of the first electrode 121 and the ionic liquid 140, and the solid/liquid interface of the active layer 130 and the ionic liquid 140 Charges are induced at the interface. Therefore, charge is induced at the two solid/liquid interfaces, which can be called an electric double layer (EDL). Electric double layers can have large capacitances due to nanogap capacitors. Therefore, even if the same gate voltage is applied, compared to the conventional FET structure, the optoelectronic device 100 according to the present embodiment can accumulate or deplete more charge carriers at the interface, thereby increasing modulation efficiency.

The ionic liquid 140 may be applied on the active layer 130 using a pipette method or spin coating. The method of applying the ionic liquid 140 is not limited to a particular embodiment, and various types of methods can be used.

The power source 150 may be connected to the electrode unit 120. The power source 150 may modulate the optical characteristics of the optoelectronic device 100 by applying a predetermined voltage to the electrode unit 120. As described above, the modulation pattern of optical properties may vary depending on the material of the active layer 130 and the sign and magnitude of the applied voltage.

The optoelectronic device 100 may further include a protective layer (not shown) covering the device. The protective layer (not shown) may be formed of a material that is transparent to the operating wavelength range of the optoelectronic device 100. For example, the protective layer (not shown) may be a cover glass as shown in FIG. 1F. For example, a protective layer (not shown) can encapsulate the ionic liquid.

Referring to FIG. 15 , the optoelectronic device 100 may have a certain level of transmittance when no voltage is applied to the first electrode 121 and the second electrode 122. For example, when 100% of the incident light passes through the active layer 130 including bismuth selenide nanoplates, 40% of the light may pass through the optoelectronic device 100. That is, for example, the transmittance of the optoelectronic device 100 to which no voltage is applied may be 40%.

Referring to FIG. 16, when a positive voltage is applied to the first electrode 121, the transmittance of the optoelectronic device 100 can be increased. For example, when 100% of the incident light passes through the active layer 130 including bismuth selenide nanoplates, 70% of the light may pass through the optoelectronic device 100. Transmittance can be increased by modulating the optical properties of bismuth selenide. In the optoelectronic device 100 according to this embodiment, the transmittance may change by more than 10% even when a positive voltage of 3V or less is applied to the first electrode 121.

Referring to FIG. 17, when a positive voltage is applied to the first electrode 121, the transmittance of the optoelectronic device 100 can be increased. For example, when 100% of the incident light passes through the active layer 130 including bismuth selenide nanoplates, 70% of the light may pass through the optoelectronic device 100. Transmittance may be reduced by modulating the optical properties of bismuth selenide. In the optoelectronic device 100 according to this embodiment, the transmittance may change by more than 10% even when a negative voltage of 3V or less is applied to the first electrode 121.

[Others of optoelectronic devices Example ]

18 to 20 describe content related to the optoelectronic device 200 according to another embodiment.

Figure 18 is a schematic plan view of an optoelectronic device 200 according to another embodiment. FIG. 19 is a schematic cross-sectional view of the optoelectronic device 200 according to FIG. 18 taken along line B-B'. FIG. 20 is a schematic cross-sectional view of the optoelectronic device 200 according to FIG. 18 taken along line C-C'.

The optoelectronic device 200 may include a substrate 210, an electrode unit 220, an active layer 230, an ionic liquid 240, and a power source 250.

The substrate 210 may be formed of a material that is transparent or translucent to light in the visible and infrared regions. The electrode unit 220 may include a first electrode 221, a second electrode 222, and a third electrode 223. The active layer 230 may be provided to be electrically insulated from the first electrode 221 and electrically connected to the second electrode 223 and the third electrode 223. Ionic liquid 240 may cover the active layer 230. The power source 250 may be connected to the electrode unit 220.

The electrode unit 220 may include a first electrode 221, a second electrode 222, and a third electrode 223. The first electrode 221 may be provided so as not to be electrically connected to the active layer 230. The first electrode 221 may function as a gate electrode. The second electrode 223 and the third electrode 223 may be provided to be electrically connected to the active layer 230. The second electrode 222 may function as a drain electrode, and the third electrode 223 may function as a source electrode. The second electrode 222 and the third electrode 223 may be provided to face each other with the active layer 230 interposed therebetween.

The optoelectronic device 200 according to this embodiment may operate in the same manner as the optoelectronic device 100 according to FIG. 14. The optical properties of the active layer 230 may be modulated depending on whether no voltage is applied to the first electrode 221, a positive voltage is applied, or a negative voltage is applied. For example, when a negative voltage is applied, the transmittance of the active layer 230 may decrease, and when a positive voltage is applied, the transmittance of the active layer 230 may increase. Since the first electrode 221, the second electrode 222, and the third electrode 223 do not cover the active layer 230, scattering of light passing through the active layer 230 can be prevented. This may be a difference between the optoelectronic device 200 according to this embodiment and the conventional FET structure.

Referring to FIGS. 19 and 20 , when voltage is applied to the first electrode 221, a predetermined current may flow from the second electrode 222 to the third electrode 223.

[smart of the window Day Example ]

Figure 21 is a schematic plan view of a smart window 300 according to an embodiment. The smart window 300 may include a plurality of optoelectronic devices 310, 320, and 330. Smart windows may require changes in optical transparency over large areas. Accordingly, by arranging a plurality of optoelectronic devices 310, 320, and 330, it is possible to implement a smart window 300 that has a fast response speed and can change transmittance even at a low voltage. The plurality of optoelectronic devices 310, 320, and 330 may change optical transmittance by applying a positive or negative voltage by the power source 340.

So far, exemplary embodiments of optoelectronic devices and smart windows have been described and illustrated in the accompanying drawings to facilitate understanding of the present invention. However, it should be understood that these examples are merely illustrative of the invention and do not limit it. And it should be understood that the present invention is not limited to the description shown and illustrated. This is because various other modifications may occur to those skilled in the art.

100: Optoelectronic device
110: substrate
120: electrode part
121: first electrode 122: second electrode
130: active layer
140: ionic liquid
150: power source

Claims (19)

In an optoelectronic device,
Board;
an electrode unit including a first electrode and a second electrode provided on the substrate;
an active layer provided between the first electrode and the second electrode, spaced apart from the first electrode, and electrically connected to the second electrode; and
It includes an ionic liquid covering the active layer,
The electrode portion and the active layer are arranged in a vertical direction on the same plane of the substrate so as not to overlap each other,
The ionic liquid covers the electrode portion and the active layer, and the ionic liquid is interposed between the first electrode and the active layer. According to claim 1,
An optoelectronic device wherein the active layer includes chalcogenide nanoplates. According to claim 2,
The chalcogenide nanoplate is Bi ₂ Se ₃ , MoSe ₂ , GaSe, MoS ₂ , WSe ₂ , WS ₂ , Bi ₂ Te ₃ , ZnSe, InSe, In ₂ Se ₃ , ReS ₂ An optoelectronic device formed of at least one of the following materials. According to claim 1,
An optoelectronic device in which the active layer is formed of a two-dimensional (2D) layered structure material. According to claim 4,
The two-dimensional material having the layered structure is an optoelectronic device formed of at least one material selected from the group consisting of Bi ₂ Se ₃ , MoSe ₂ , black phosphorus, ZnO, GaAs, Ge, and Si. According to claim 1,
An optoelectronic device wherein the thickness of the active layer is 20 nanometers or less. According to claim 1,
The ionic liquids are [DEME][TFSI], [DEME][BF4], [EMIM]-[BF4], [BMIM][BF4], [BMIM][TFSI], [TMPA][BF4], [DEME] [FSI], [EMIM] An optoelectronic device including at least one of [FSI]. According to claim 1,
An optoelectronic device further comprising a power source coupled to the electrode unit and modulating optical characteristics of the optoelectronic device. According to claim 8,
The power source modulates transparency of the optoelectronic device by applying a voltage of -3V to 3V to the electrode portion. According to claim 1,
The optoelectronic device is provided so that the first electrode is not electrically connected to the active layer. According to claim 1,
The substrate is glass, sapphire, quartz, silicon dioxide, silicon nitride, gallium nitride, plastics, and boron nitride. , ITO, AZO, IZO, FTO, CdO, CdZnO, CdNiO, PEDOT, and graphene. An optoelectronic device formed of at least one material. According to claim 1,
The electrode unit further includes a third electrode provided on the substrate. According to claim 12,
The first electrode functions as a gate electrode that is not electrically connected to the active layer, the second electrode is electrically connected to the active layer and functions as a drain electrode, and the third electrode is electrically connected to the active layer and serves as a source. Optoelectronic devices that function as electrodes. According to claim 12,
The third electrode is provided on the same plane as the first electrode and the second electrode on the substrate. According to claim 1,
An optoelectronic device further comprising a protective layer covering the device. According to claim 15,
The optoelectronic device wherein the ionic liquid is encapsulated by the protective layer. According to claim 1,
The ionic liquid is an optoelectronic device that covers the active layer by spin coating or pipette method. According to claim 1,
The active layer is an optoelectronic device having any one of the following shapes: square, circle, triangle, oval, rectangle, hexagon, or polygon. A plurality of optoelectronic devices according to claim 1; and
A power source coupled to the plurality of optoelectronic devices and modulating optical characteristics of the plurality of optoelectronic devices.

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