Organic electroluminescent device including light extraction layer

Abstract

Disclosed is an organic electroluminescent device including a light extraction layer. The present disclosure may be composed of an organic electroluminescent device, in which an organic electroluminescent device including a light extraction layer is provided with a substrate, a first electrode, one or more organic layers including a blue light emitting layer, a second electrode, and the light extraction layer in this order, and the light extraction layer includes a material satisfying the following conditions (1) to (3). Wherein condition (1) n ((at) 450nm) > = 2.00, condition (2) k (at) 420nm > = 0.10, and condition (3) k (at) 450nm < = 0.01, where n represents a refractive index in a defined wavelength and k represents an absorbance coefficient in the defined wavelength. Therefore, the organic electroluminescent device can improve the external luminous efficiency and color purity of the light extraction layer.

Description

Technical Field

[0001] The present invention relates to an organic electroluminescent device, in particular to an organic electroluminescent device comprising a light extraction layer. Background Art

[0002] The luminous efficiency of an organic electroluminescent device is divided into internal luminous efficiency and external luminous efficiency. The external luminous efficiency is the internal luminescence of the organic layer introduced between the first electrode and the second electrode. About 20% of the internal luminescence is radiated to the outside through an optical process, and about 80% disappears in the optical process.

[0003] Thus, in order to prevent the disappearance of light in the optical process and improve the external luminous efficiency, various organic compounds with high refractive index are used as light extraction layer materials in the light extraction layer. So far, even external luminous materials are also striving to develop organic compounds with high refractive index and stability that can improve the external luminous efficiency. However, organic electroluminescent devices emit blue light in the luminescent wavelength region around 440nm to 510nm. Therefore, in the light extraction layer with a high refractive index, part of the light in the 440nm to 450nm segment is absorbed, which leads to a decrease in efficiency and a decrease in color purity.

[0004] Furthermore, UV light existing in nature or UV light generated during the thin film encapsulation process (TFE: Thin Film Encapsulation) can cause the degeneration of the light-emitting layer and the functional layer.

[0005] In order to increase light extraction capacity, high refractive index organic compounds are being developed, and efforts are continuing to develop organic compounds that are stable to UV light, which is a factor that shortens the life of equipment during manufacturing and use.

[0006]

Prior technical literature

[0007] [Patent Literature]

[0008] Korean Patent Publication No. 10-2004-0098238 Summary of the invention

[0009] Problem that the invention aims to solve

[0010] The object of the present invention is to enable an RGB image display device to better extend the service life of the device.

[0011] Usually, in order to improve light extraction, a high-refractive light extraction layer is stacked. Patent Document 1 uses an organic light extraction layer with a refractive index of 1.7 or more and a film thickness of 60nm on the upper electrode of an organic EL device to make a film, thereby improving the luminous efficiency of red and green light-emitting devices by about 1.5 times.

[0012] The purpose is to improve the lifespan by making the light-emitting wavelength of the light-emitting layer of the RGB image display device belong to the absorption band of the light extraction layer, thereby not reducing its own light absorption efficiency, but also preventing the instrument lifespan from being shortened by the UV light present in natural light, and absorbing the UV light source that may occur in the instrument manufacturing process to extend the instrument lifespan.

[0013] However, the purpose of the present invention is not limited to the above content. Of course, even if not explicitly mentioned, the purpose or effect that can be understood through the solution or implementation method will be included therein.

[0014] Means used to solve problems

[0015] In order to achieve the above-mentioned purpose, the present invention is composed of an organic electroluminescent device, which comprises a substrate, a first electrode, one or more organic layers including a blue light-emitting layer, a second electrode, and a light extraction layer in sequence, wherein the light extraction layer comprises a material satisfying the following conditions (1) to (3).

[0016] Among them, condition (1) n(@450nm)≥2.00,

[0017] Condition (2)k@420nm≥0.10,

[0018] Condition (3)k@450nm≤0.01,

[0019] Here, n represents the refractive index at the defined wavelength, and k represents the absorption coefficient at the defined wavelength.

[0020] It may be composed of an organic electroluminescent device, which is composed of the second electrode comprising a metal.

[0021] It may be composed of an organic electroluminescent device, wherein the film thickness of the light extraction layer is less than 200 nm.

[0022] It can be composed of an organic electroluminescent device, wherein the PL spectrum peak wavelength of the luminescent material contained in the blue luminescent layer is greater than 430nm and less than 500nm.

[0023] It may be composed of an organic electroluminescent device, wherein the organic layer further includes a red light-emitting layer and a green light-emitting layer.

[0024] The light extraction layer for an organic electroluminescent device may be composed of a light extraction layer having a refractive index of 2.20 or more at a wavelength of 450 nm in the condition (1).

[0025] Effects of the Invention

[0026] The organic electroluminescent device of the present invention comprises a light extraction layer, and the light extraction layer comprises a compound for a light extraction layer having a refractive index (n) of 2.0 or more at a wavelength of 450 nm, thereby achieving high efficiency.

[0027] Specifically, the light extraction layer is formed to obtain high efficiency in both the blue device and the green and red devices.

[0028] Furthermore, the organic light-emitting device described in the present invention utilizes a light extraction layer compound having an absorption coefficient (k) of greater than 0.1 at 420 nm and less than 0.01 at 450 nm to form a light extraction layer, thereby blocking the possibility of efficiency reduction and color change caused by absorption in the visible light region, and absorbing UV light that may be exposed during the manufacturing process and use of the instrument, which helps the instrument composed of the organic electroluminescent device to maintain a long life.

[0029] Hereinafter, the above-mentioned effects and additional effects will be described in detail.

[0030] Meanwhile, various beneficial advantages and effects of the present invention are not limited to the above contents, which can be more easily understood in the process of describing the specific embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic cross-sectional view of an organic light-emitting device according to an embodiment of the present invention.

[0032] Figure 2 The graph shows the blue wavelength spectrum generated by the organic electroluminescent device and the absorption coefficient chart of various comparative compounds in the range of 380nm to 530nm.

[0033] Description of Reference Numerals

[0034] 100: Substrate

[0035] 110: First electrode

[0036] 200: Organic layer

[0037] 210: Hole injection layer

[0038] 215: Charge generation layer

[0039] 220: Luminous layer

[0040] 230: Electron transport layer

[0041] 235: Electron injection layer

[0042] 120: Second electrode

[0043] 300: Light extraction layer DETAILED DESCRIPTION

[0044] The present invention is susceptible to numerous modifications and various forms, and specific embodiments are illustrated in the accompanying drawings and described in detail herein.

[0045] However, it does not limit the disclosed form of the specific invention. Unless otherwise described, all technical terms and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art.

[0046] Hereinafter, the present invention is described in further detail.

[0047] The light extraction layer for the organic electroluminescent device described in the embodiment of the present invention may meet the following conditions.

[0048] Condition (1) n(@450nm)≥2.00

[0049] Condition (2)k@420nm≥0.10

[0050] Condition (3)k@450nm≤0.01

[0051] At this time, n represents the refractive index in a defined wavelength.

[0052] The k represents the absorption coefficient in a defined wavelength.

[0053] The organic electroluminescent device described in the present invention has a refractive index of 2.25 or more at a wavelength of 450nm, an absorption coefficient of 0.10 or more at 420nm, and a light extraction layer of a compound having an absorption coefficient of 0.01 or less at 450nm, thereby achieving high efficiency and long life.

[0054] Specifically, the light extraction layer for the organic electroluminescent device of the present invention adopts a high refractive index light extraction material with a refractive index of 2.0 or more at a wavelength of 450nm under the condition (1). When the light extraction layer has an absorption coefficient of 0.10 or more at 420nm, it can effectively absorb high energy in the UV region during instrumentation and use, thereby minimizing damage to organic matter in the organic electroluminescent device, thereby helping to increase the service life of the organic electroluminescent device.

[0055] Furthermore, when the absorption coefficient is 0.01 or less at 450 nm, the light emitted from the organic electroluminescent device is not absorbed, which helps to improve efficiency and color purity.

[0056] The organic electroluminescent device of the present invention is further described below in detail.

[0057] Figure 1 FIG. 1 is a schematic cross-sectional view of an organic light-emitting device according to an embodiment of the present invention. Figure 1As shown, the organic light-emitting device described in one embodiment may include a first electrode 110, a hole injection layer 210, a charge generation layer 215, a light-emitting layer 220, an electron transport layer 230, an electron injection layer 235, a second electrode 120, and a light extraction layer 300 stacked in sequence on a substrate 100.

[0058] The first electrode 110 and the second electrode 120 are disposed opposite to each other, and an organic layer 200 may be disposed between the first electrode 110 and the second electrode 120. The organic layer 200 may include a hole injection layer 210, a charge generation layer 215, a light emitting layer 220, an electron transport layer 230, and an electron injection layer 235.

[0059] In addition, in the light extraction layer 300 of the present invention, the light extraction layer can be disposed outside of any one or more of the first electrode and the second electrode.

[0060] Specifically, of the two side surfaces of the first electrode or the second electrode, the side adjacent to the organic layer sandwiched between the first electrode and the second electrode is called the inner side, and the side not adjacent to the organic layer is called the outer side. That is, when the light extraction layer is disposed on the outer side of the first electrode, the first electrode is sandwiched between the light extraction layer and the organic layer, and when the light extraction layer is disposed on the outer side of the second electrode, the second electrode is sandwiched between the light extraction layer and the organic layer.

[0061] Furthermore, in the organic light-emitting device described in an embodiment of the present invention, the inner sides of the first electrode and the second electrode may contain more than one layer of multiple organic layers, and the outer sides of any one or more of the first electrode and the second electrode may be formed with a light extraction layer. That is, the outer sides of the first electrode and the second electrode may both be formed with a light extraction layer, or only the outer sides of the first electrode or the second electrode may be formed with a light extraction layer.

[0062] At this time, the refractive index of the light extraction layer at a wavelength of 450 nm may be greater than 2.0, specifically, greater than 2.2, and the absorption coefficient may be greater than 0.10 at 420 nm and less than 0.01 at 450 nm.

[0063] like Figure 1 As shown, in the organic light emitting device according to an embodiment, the first electrode 110 has conductivity. The first electrode 110 can be formed of a metal alloy or a conductive compound. The first electrode 110 is usually an anode, but the function of the electrode is not limited.

[0064] The first electrode 110 is formed on the substrate 100 using an electrode material by deposition, electron beam evaporation or sputtering. In order to easily inject holes into the organic light emitting device, the material of the first electrode 110 can be selected from materials with a high work function.

[0065] The light extraction layer 300 proposed by the present invention is only applicable when the light emission direction of the organic light emitting device is top emission, therefore, the first electrode 110 is a reflective electrode. It can be made of metal materials. For example, non-oxide Mg (magnesium), Al (aluminum), Al-Li (aluminum-lithium), Ca (calcium), Mg-In (magnesium-indium), Mg-Ag (magnesium-silver). Recently, carbon substrate flexible electrode materials can be used, such as CNT (carbon nanotube), Graphene (graphene), etc.

[0066] The organic layer 200 may be formed of multiple layers. When the organic layer 200 is formed of multiple layers, the organic layer 200 may include hole transport regions 210 to 215 disposed on the first electrode 110 , a light emitting layer 220 disposed on the hole transport regions, and electron transport regions 230 to 235 disposed on the light emitting layer 220 .

[0067] At the same time, the hole injection layer 210 can be formed by depositing a hole injection layer material on the upper part of the first electrode 110 by vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) method, etc. When the hole injection layer 210 is formed by the vacuum deposition method, the deposition conditions are different according to the compound used as the hole injection layer 210 material, the structure and thermal properties of the target hole injection layer 210, etc., but usually, the deposition temperature is 50-500°C, the vacuum degree is 10-8 to 10-3 torr, the deposition rate is 0.01 to 100 / sec, and the layer thickness range is 10 to 5μm. In addition, the surface of the hole injection layer 210 is further deposited with a charge generation layer 215 as needed. The charge generation layer material can be a conventional material, for example, HATCN.

[0068] At the same time, the light-emitting layer material is deposited on the upper part of the hole transport layer 210 or the charge generation layer 215 by vacuum deposition, spin coating, casting, LB method, etc. to form the light-emitting layer 220. When the light-emitting layer 220 is formed by the vacuum deposition method, its deposition conditions are different according to the compounds used, and it is generally preferred to select conditions that are almost the same as those for the formation of the hole injection layer 210.

[0069] The light-emitting layer material may use a known compound as a base or a dopant.

[0070] Among them, when phosphorescent dopants are used together in the light-emitting layer material, in order to prevent the triple excitons or holes from diffusing to the electron transport layer 230, a hole suppression material (HBL) can be further deposited on the upper part of the light-emitting layer 220 by vacuum deposition or spin coating. The hole suppression material that can be used is not particularly limited, and any known material can be selected. For example, there are oxadiazole derivatives or triazole derivatives, phenanthroline derivatives or hole suppression materials described in Japanese Patent Laid-Open No. 11-329734 (A1), and representative Balq (bis (8-hydroxy-2-hydroxymethylquinoline) -biphenyl oxide aluminum), phenanthroline (phenanthrolines) compounds (for example: UDC company BCP (Bathocuproine) and the like can be used. In this way, the light-emitting layer 220 described in the present invention can include more than one layer or more than two layers of blue light-emitting layers.

[0071] Furthermore, the electron transport layer 230 is formed on the upper part of the light emitting layer 220 and can be formed by vacuum deposition, spin coating, casting, etc. The deposition conditions of the electron transport layer 230 can be different according to the compound used, but, generally, it is appropriate to select the conditions that are almost the same as those for forming the hole injection layer 210.

[0072] Furthermore, an electron injection layer material may be deposited on the upper portion of the electron transport layer 230 to form the electron injection layer 235 , which may be formed by vacuum deposition, spin coating, casting, or the like.

[0073] Meanwhile, the second electrode 120 is used as an electron injection electrode, which can be formed on the upper part of the electron injection layer 235 by vacuum deposition or sputtering. Various metals can be used as the material of the second electrode 120. Specific examples include aluminum, gold, silver, magnesium and the like, but are not limited thereto.

[0074] The organic light-emitting device described in the present invention can not only be an organic electroluminescent device including the above-mentioned light extraction layer 300, first electrode 100, hole injection layer 210, charge generation layer 215, light-emitting layer 220, electron transport layer 230, electron injection layer 235, second electrode 120 and light extraction layer 300 structure, but also an organic electroluminescent device further adding one or two intermediate layers as needed.

[0075] In addition, the thickness of each organic layer formed according to the present invention can be adjusted to the required degree, specifically, it can be 1 to 1,000 nm, more specifically, it can be 1 to 150 nm. The light extraction layer 300 can be formed on the two side surfaces of the first electrode 110, the outer side surface where the hole injection layer 210 is not formed. And, it can be formed on the two side surfaces of the second electrode 120, the outer side surface where the electron injection layer 235 is not formed, but it is not limited here. The light extraction layer 300 can be formed by a deposition process, and the thickness of the light extraction layer 300 is 100 to 2,000, more specifically, it can be 300 to 1,000. In this way, the transmittance of the light extraction layer 300 can be prevented from decreasing by adjusting the thickness.

[0076] And, although Figure 1 Although not shown, according to an embodiment of the present invention, an organic layer having multiple functions may be further formed between the light extraction layer 300 and the first electrode 110 or between the light extraction layer 300 and the second electrode 120. Alternatively, an organic layer having multiple functions may be further formed on the upper portion (outer surface) of the light extraction layer 300, which is not limited thereto.

[0077] In the organic light-emitting device, as voltages are applied to the first electrode 110 and the second electrode 120, holes injected from the first electrode 110 migrate to the light-emitting layer 220 via the hole transport regions 210-215, and electrons injected from the second electrode 120 migrate to the light-emitting layer 220 via the electron transport regions 230-235. Electrons and holes recombine in the light-emitting layer 220 to generate excitons, which fall to the ground state in an excited state and emit light.

[0078] The light path generated by the light emitting layer 220 can show extremely different tendencies according to the refractive index of the organic / inorganic substances constituting the organic light emitting device. Among the light passing through the second electrode 120, only the light transmitted at an angle less than the critical angle of the second electrode 120 can pass through. In addition, the light contacting the second electrode 120 at a greater angle than the critical angle is totally reflected or reflected and cannot be radiated to the outside of the organic light emitting device.

[0079] When the refractive index of the light extraction layer 300 is high, this total reflection or reflection phenomenon is reduced, which helps to improve the luminous efficiency. Moreover, when it has an appropriate thickness, the micro-cavity phenomenon is maximized, which helps to significantly improve the efficiency and color purity.

[0080] The light extraction layer 300 is located at the outermost edge of the organic light emitting device. While it has no effect on the driving of the device, it also has a great effect on the characteristics of the device. Therefore, the light extraction layer 300 not only plays a protective function on the inside of the organic light emitting device, but also improves the characteristics of the device. Both aspects are important. Organic matter absorbs light energy in a specific wavelength range, which depends on the energy band gap. When the energy band gap is adjusted to absorb the UV region, including the improvement of the optical characteristics of the light extraction layer 300, it can be used to protect the organic light emitting device, and the UV region can affect the organic matter in the organic light emitting device.

[0081] The organic light emitting device of the present invention can be a top-emitting type, a back-emitting type or a dual-emitting type according to the materials used.

[0082] In order to specifically describe this specification, embodiments will be given for detailed description. However, the embodiments described in this specification can be transformed into a variety of other forms, and it should not be interpreted that the scope of this application is limited to the embodiments described in detail below. The embodiments of this application are used to more comprehensively describe this specification for those skilled in the art.

[0083] <Test Example 1>

[0084] Refractive index and absorption coefficient detection method

[0085] In <Test Example 2>, the refractive index (n) and the absorption coefficient (k) of the prepared compound for the light extraction layer were measured using an Ellipsometer instrument produced by JAWOOLLAM.

[0086] Preparation of test strips for testing:

[0087] In order to detect the optical properties of the compound, the silicon substrate was cleaned with ethanol (Ethanol), deionized water (DIWater), acetone (Acetone) and ultrasound (Ultrasonic) for 20 minutes respectively, and then the compound was placed on the cleaned silicon substrate. Then, in a vacuum degree of 2.0x10-7Torr, a deposited film with a thickness of 50nm was formed at a speed of 1 / sec to prepare a test piece.

[0088] The refractive index and absorption coefficient of the prepared test piece were detected in the wavelength range of 380nm to 530nm using the ellipsometer device.

[0089] <Test Example 2>

[0090] Preparation of organic electroluminescent devices

[0091] Table 1 records the structure of a conventional organic light-emitting device. The organic light-emitting device prepared as an example in the present invention is stacked in order from the bottom: first electrode 110 / hole injection layer 210 / charge generation layer 215 / luminescent layer 220 / electron transport layer 230 / electron injection layer 235 / second electrode 120 / light extraction layer 300.

[0092] The hole injection layer 210 , the charge generation layer 215 , the light emitting layer 220 , the electron transport layer 230 , and the electron injection layer 235 use materials listed in Table 1 below.

[0093] The second electrode 120 for injecting electrons is formed on the electron injection layer 235. Various metals can be used as the cathode.

[0094] Furthermore, a light extraction layer 300 is formed on the second electrode 120 .

[0095]

Table 1

[0096]

[0097] Table 2 below records the structural formulas of the materials used in the light extraction layer in Comparative Example 1 and Examples 1 to 4.

[0098]

Table 2

[0099]

[0100]

[0101] <Comparative Example 1>

[0102] A glass substrate is provided, and a reflective layer containing Ag is formed on the upper part of the substrate to serve as a reflective film of the first electrode, and ITO is deposited on the upper part of the reflective film formed using the Ag. Next, on the upper part of the ITO, HIL-1 is formed into a 100nm film as an organic film layer on the hole injection layer, and a mixture of HIL-1 and HIL-2 (9:1, wt. / wt.) is formed into a 10nmf film as a charge generation layer. Then, on the substrate BH01, a 2 wt% coating dopant BD01 is formed into a 25nm film as a light-emitting layer. On the electron transport layer, a mixture of ET01 and Liq (1:1, wt. / wt.) is formed into a 30nm thickness, and then LiF is deposited into a 1nm thickness to form an electron injection layer. Next, MgAg is deposited into a 15nm thickness as the second electrode, and on the second electrode, Figure 2 The Alq3 shown was deposited at 60 nm and used as a light extraction layer. The device thus prepared was encapsulated in a glove box to prepare an organic electroluminescent device.

[0103] <Example 1> to <Example 4>

[0104] The same method as that of Comparative Example 1 was adopted to prepare an organic electroluminescent device using a light extraction layer to form a film using the k-Test1, k-Test2, k-Test3, and k-Test4 compounds listed in Table 2 above.

[0105] <Test Example 3>

[0106] Performance evaluation of organic electroluminescent devices

[0107] In the evaluation of efficiency and color coordinates, a voltage was applied through a Kiethley 2400 source measurement unit to inject electrons and holes, and the brightness and color coordinates of the light were measured using a Konica Minolta CS-2000 spectroradiometer.

[0108] The same equipment as used in the lifetime evaluation was used to detect changes in brightness at 10mA / cm2. In order to reproduce daily usage conditions (Lighting Room), the lifetime was evaluated while the test piece in the test room was evenly irradiated with LED light (the test was carried out in a dark room after the lights were turned off).

[0109] In order to evaluate the life of the material itself, a darkroom was arranged and the life was evaluated. The changes in life under daily use and the changes in life under the evaluation of the material itself were detected and compared. The results are also recorded in Table 3.

[0110]

Table 3

[0111]

[0112] According to the results of Experimental Example 1 and Experimental Example 3, the absorption coefficients of various materials at different wavelengths and the luminescence spectra at different wavelengths are shown in Figure 2 middle.

[0113] like Figure 2 As shown, from the absorption coefficients of various light extraction materials at different wavelengths, it can be seen that they can absorb the light generated by the light-emitting layer (EML) and also absorb the UV generated in nature or in the preparation of organic electroluminescent devices.

[0114] From the results of Comparative Example 1 and Examples 1 to 4, it can be confirmed that when the material satisfying the condition (1) of claim 1 is used in the light extraction layer, the efficiency can be significantly improved.

[0115] It was also confirmed that in a darkroom, the lifespan of all materials is similar, but when a material satisfying condition (2) is used as a light extraction layer, the lifespan in a darkroom can be improved.

[0116] Materials that exceed condition (3) can improve efficiency due to high refraction, but CIE_y increases sharply and BI decreases. It can be seen that they can eventually partially absorb the light generated by the light extraction layer itself in the light-emitting layer.

[0117] From the above, it can be confirmed that the higher the refractive index of the light extraction layer, the higher the efficiency. When the instrument is actually used in a natural environment, materials with an absorption coefficient of k@420nm≥0.10 can actually increase the service life. Materials with an absorption coefficient of k@450nm≤0.01 inevitably absorb the light generated by the light-emitting layer, thereby realizing high-efficiency, long-life, and high-color-purity organic electroluminescent devices.

[0118] The present invention is shown or described above by means of preferred embodiments illustrating the principles of the present invention, but the present invention is not limited to the configurations and functions shown and described above. A person skilled in the art of the present invention should carefully understand that various changes and modifications can be made to the present invention without departing from the concept and scope of the appended claims. Therefore, all reasonable changes and modifications and equivalents thereof should also be regarded as belonging to the scope of the present invention.

[0119] Industrial Applicability

[0120] As described above, the present invention can be widely used in the industrial field of organic electroluminescent devices.

Claims

1. An organic electroluminescent device, characterized in that: The invention comprises a substrate, a first electrode, one or more organic layers including a blue light-emitting layer, a second electrode, and a light extraction layer in sequence, wherein the light extraction layer comprises a material satisfying the following conditions (1) to (3), Among them, condition (1) n(@450nm)≥2.00, Condition (2)k@420nm≥0.10, Condition (3)k@450nm≤0.01, Wherein, n represents the refractive index at a defined wavelength, and k represents the absorption coefficient at a defined wavelength.

2. The organic electroluminescent device according to claim 1, characterized in that: The second electrode is composed of a metal.

3. The organic electroluminescent device according to claim 1, characterized in that: The light extraction layer has a thickness of 200 nm or less.

4. The organic electroluminescent device according to claim 1, characterized in that: The PL spectrum peak wavelength of the light-emitting material contained in the blue light-emitting layer is greater than or equal to 430 nm and less than or equal to 500 nm.

5. The organic electroluminescent device according to any one of claims 1 to 4, characterized in that: The organic layer further includes a red light emitting layer and a green light emitting layer.

6. The light extraction layer for an organic electroluminescent device according to claim 1, characterized in that: The refractive index at a wavelength of 450 nm in the above condition (1) is 2.20 or more.

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