Transparent display device

Abstract

Transparent display device comprising the following: a substrate (100) with multiple pixels (P); at least one emission section (E) and at least one transmission section (T) in each of the pixels (P); an organic light emission layer (132a, 132b, 132c) in the emission section (E); a reflective electrode structure (111) between the organic light emission layer (132a, 132b, 132c) and the substrate in the emission section (E); a transparent electrode (140) located above the emission section (E) and the transmission section (T) throughout the pixels (P) above the substrate (100); a cover structure (170) comprising a first cover layer (171) over the transparent electrode (140) having destructive interference properties and a first refractive index n1, and a second cover layer (172) configured over the first cover layer (171) having a second refractive index n2 that is smaller than the first refractive index n1; and an encapsulation layer (300); wherein light reflected downwards at an interface between the transparent electrode (140) and the cover structure (170) and light reflected downwards at an interface between the cover structure (170) and the encapsulation layer (300) have opposite phases.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The present invention relates to a display device and, more particularly, to a transparent display device having improved transmittance and improved luminous uniformity according to wavelength. Discussion of related technology

[0002] Since recently entering the information age, the field of displays that visually display electrical information signals has been rapidly developed, and in order to meet this development, various flat display devices with excellent performance such as thinness, light weight and low power consumption are being developed, which are rapidly replacing the conventional cathode ray tubes (CRT).

[0003] As examples of the flat display devices, there are a liquid crystal display device (LCD device), a plasma display panel device (PDP device), a field emission display device (FED device), an organic light-emitting diode (OLED) display device, a quantum dot display device, etc.

[0004] Among them, self-luminous display devices that do not require separate light sources and achieve compactness and clear color display, such as organic light-emitting diode display devices and quantum dot display devices, are considered as competitive applications.

[0005] A self-luminous display device includes a plurality of pixels above / on a substrate, each pixel including a light-emitting diode having an anode and a cathode arranged opposite each other and a light-emitting layer provided between the anode and the cathode.

[0006] Because the self-luminous display device displays an image using the light emitted by the LEDs, it is important to effectively utilize the light extracted from the LEDs. Therefore, efforts have been made to reduce the thickness of the cathode arranged in a light-emitting direction to increase transmittance, and efforts have been made to increase the reliability of the cathode and the elements arranged adjacent to it to stabilize the performance of the display device.

[0007] In a top emission structure currently in use, an anode of a light-emitting device contains a reflective metal, and a cathode of the light-emitting device contains a transflective metal. Therefore, light emitted from a light-emitting layer located between the anode and the cathode is reflected by the reflective anode, resonating several times between the anode and the cathode, and emitting light of a specific wavelength according to the distance between the anode and the cathode. In such a structure, efforts are made to reduce the thickness of the cathode to further increase transmittance.

[0008] Furthermore, the need for a transparent display device that can transmit light through its front and back surfaces and display an image without obstructing the field of view is now increasing.

[0009] The transparent display device varies the arrangement of the light-emitting diodes in a self-luminous region and a transparent region and can thus achieve both a transparent display effect and a luminous display effect.

[0010] However, because the self-luminous region and the transparent region consider the increase of luminous efficiency and transmittance as important, the self-luminous region and the transparent region have different purposes and consequently require different structures, thereby making it difficult to implement the self-luminous region and the transparent region by a common formation method.

[0011] Furthermore, if both the self-luminous region and the transparent region are provided over a substrate, the transparent region requires omission of some elements compared with the elements of the self-luminous region in order to increase transmittance, an emission region is reduced relative to the transparent region, and the required driving voltage to emit light of a certain luminance or more only through the reduced emission region is high.

[0012] Recently, in a transparent display device, the thickness of an electrode or a cover layer located in the light emission direction is reduced in order to increase the transmittance, in which case deviations occur between the intensities of the light emitted from the emission regions according to the wavelength, consequently the color purity is reduced and the color efficiency is reduced.

[0013] That is, it is difficult for transparent display devices that have been proposed so far to have high transmittance and uniform color efficiency according to wavelength.

[0014] US 2015 / 0 187 847 A1 relates to an OLED device comprising a substrate defining a plurality of subpixel regions including red, green, and blue subpixel regions; a first electrode formed on the substrate; an organic emission layer formed on the first electrode; a second electrode formed on the organic emission layer; and a capping layer formed on the second electrode. The capping layer is formed to include an optical matching material that increases in proportion to a wavelength of incident light.

[0015] US 2014 / 0 138 636 A1 relates to an organic light-emitting display device having a light extraction prevention layer between a display unit arranged on a substrate and an encapsulation layer for protecting the display unit.

[0016] JP 2005 - 107 137 A relates to an anti-reflection film and a transparent base material provided with the anti-reflection film.

[0017] US 2011 / 0 084 291 A1 relates to an organic light-emitting diode display comprising a substrate main body, a plurality of organic light-emitting diodes formed on the substrate main body, and a differential capping layer covering the plurality of organic light-emitting diodes. The differential capping layer has a plurality of thicknesses. The differential capping layer has first regions with a thickness of 90 nm to 120 nm and second regions with a thickness less than the thickness of the first regions. SUMMARY OF THE INVENTION

[0018] Accordingly, the present invention is directed to a transparent display device that substantially obviates one or more problems due to the limitations and disadvantages of the prior art.

[0019] It is an object of the present invention to provide a transparent display device which can exhibit both a transparent display effect and a luminous display effect and thereby can exhibit improved transparency and uniformity of color efficiency according to wavelength.

[0020] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows, and in part will become apparent to those of ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims, as well as in the accompanying drawings.

[0021] The object is achieved by the features of the independent claims. Preferred embodiments are specified in the dependent claims and the description.

[0022] The problem is solved by the features of the independent claims.

[0023] The first refractive index can be 2.0 to 2.7, while the second refractive index can be 1.3 to 2.0.

[0024] The first cover layer may have a first thickness (d1), wherein a first optical path length (n1d1) of the first cover layer may have a value of mλ / 2cosθ (where m is an integer, λ is a wavelength of destructive interference, and θ is an angle of incidence).

[0025] The wavelength of destructive interference can be a blue wavelength.

[0026] A peak wavelength of destructive interference can be in the range of 430 nm to 465 nm.

[0027] The second cover layer may have a second thickness (d2), wherein a second optical path length (n2d2) of the second cover layer may be 0.9 to 1.1 times the first optical path length (n1d1).

[0028] A difference between the reflectance of a top surface of the second cover layer and a reflectance of an interface between the first cover layer and the second cover layer may be within 5%.

[0029] The transparent display device may further include an encapsulation layer over the second cover layer having a small refractive index change according to wavelength that is 0.2 or less in a visible wavelength range.

[0030] The reflectance of a top side of the second cover layer can (n2 cosθi−nEncap cosθtn2 cosθi+nEncap cosθt)2 (where nEncap is a refractive index of an element located above the second cap layer, θi is an angle of incidence, and θt is an angle of exit).

[0031] The reflectance of an interface between the first cover layer and the second cover layer can (n1 cosθi−n2 cosθtn1 cosθi+n2 cosθt)2 (where θi is an angle of incidence and θt is an angle of emergence), wherein the difference between the reflectance of the interface between the first cover layer and the second cover layer and the reflectance of the top surface of the second cover layer may be 5% or less.

[0032] The first thickness can be 25.0 nm to 50.0 nm, while the second thickness can be 30.0 nm to 70.0 nm.

[0033] The light emitted through a top surface of the organic light-emitting layer may be transmitted sequentially through the transmissive electrode, the first cap layer, and the second cap layer, wherein an amount of light transmitted through the second cap layer may be proportional to a value obtained by subtracting the reflectance of the transmissive electrode, the reflectance of the interface between the first cap layer and the second cap layer, and the reflectance of the top surface of the second cap layer from the total amount of light emitted through the top surface of the organic light-emitting layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate the embodiment(s) of the invention and together with the description serve to explain the principle of the invention; in which: Fig. 1 is a plan view of a transparent display device according to the present invention; Fig. 2 is a cross-sectional view illustrating a transparent display device according to a first embodiment of the present invention; Fig. 3A and Fig. 3B views illustrating the principles of destructive interference and constructive interference, respectively; Fig.4 is a schematic view illustrating the transmittance and reflectance properties at the cover layers and the interfaces in the transparent display device according to the present invention; Fig. 5 a graphical representation showing the permeabilities of different deck structures; Fig. 6 is a graphical representation showing the intensities of blue light emitted by the respective cover structures; Fig. 7A to 7C are cross-sectional views illustrating transparent display devices according to various experimental examples according to the arrangement of a second electrode located in a light emission direction and a cover structure; Fig. Figure 8 is a graphical representation showing the transmittances of the transparent display devices according to the Fig. 7A to 7C; Fig.9 is a schematic cross-sectional view illustrating the transmittance and reflection characteristics of the cover layers and the interfaces in the transparent display device according to a third experimental example and the transparent display device according to the present invention; Fig. 10A to 10C are graphs showing the trends of transmittance of blue, green, and red light according to the application of the thicknesses of the respective coating layers of the coating structure of the transparent display device according to the present invention; Fig. 11A and Fig.11B are graphs showing transmittances and spectra in test examples in which a high-refractive-index cap layer is used as a single cap layer, but the high-refractive-index cap layer is set to have different destructive interference characteristics and constructive interference characteristics; Fig. 12A and Fig. 12B are graphs illustrating the transmittances and spectra of a capping structure formed by stacking a capping layer having a high refractive index and destructive interference properties and a capping layer having a low refractive index, another capping structure, and a single capping layer having a high refractive index and constructive interference properties; Fig.13A to 13C are graphs showing the spectra of test examples of a single cap layer having destructive interference characteristics, a single cap layer having constructive interference characteristics, and the cap structure according to the present invention when blue light, green light, and red light are emitted, respectively; Fig. 14 is a plan view illustrating a transparent display device according to a second embodiment of the present invention; Fig. 15 one along line II' to Fig. 14 taken cross-sectional view; and Fig. 16 is a cross-sectional view illustrating a transparent display device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Furthermore, the names of the elements used in the following description of the embodiments of the present invention are chosen for ease of preparation of the description, and thus may differ from the names of parts of an actual product.

[0036] The shapes, sizes, speeds, angles, numbers, etc. disclosed in the drawings to describe the embodiments of the present invention are only examples and do not limit the present invention. In the following description of the embodiments and the drawings, the same or similar elements are denoted by the same reference numerals even if they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of the known functions and configurations included herein will be omitted if it might make the subject matter of the present invention rather unclear. In the following description of the embodiments, the terms 'include', 'comprise', 'consist of', etc.interpreted to indicate the presence of one or more other properties, numbers, steps, operations, elements, or parts set forth in the description, or combinations thereof, and do not exclude the presence of, or the possibility of adding, any properties, numbers, steps, operations, elements, parts, or combinations thereof, unless the term 'only' is used. It is recognized that a singular expression of an element includes a plural expression of the element unless otherwise specified.

[0037] In interpreting the elements included in the various embodiments of the present invention, it is interpreted that the elements contain areas of error even if there is no clear statement.

[0038] In the following description of the embodiments, it will be appreciated that when expressing positional relationships, e.g., when an element is 'on, 'over,' 'under,' 'next to,' etc., another element, the two elements may be in direct contact with each other or one or more other elements may be interposed between the two elements, unless the term 'exactly' or 'directly' is used.

[0039] In the following description of the embodiments, it will be recognized that when expressing temporal relationships, e.g., a term expressing a sequence of events such as 'after', 'subsequent to', 'after', or 'before', may encompass a continuous relationship between the events or a discontinuous relationship between the events unless the term 'exactly' or 'directly' is used.

[0040] In the following description of the embodiments, it will be appreciated that when the terms 'first,' 'second,' etc., are used to describe different elements, these terms are merely used to distinguish the same or similar elements. Therefore, an element modified by the term 'first' may be the same as an element modified by the term 'second,' within the technical scope of the invention, unless otherwise specified.

[0041] The features of the various embodiments of the present invention may be partially or entirely interconnected or combined and technically differently driven and interlocked with each other, wherein the respective embodiments may be implemented independently or jointly implemented in conjunction with each other.

[0042] Fig.1 is a plan view of a transparent display device according to the present invention, Fig. Fig. 2 is a cross-sectional view illustrating a transparent display device according to a first embodiment of the present invention, and Fig. 3A and Fig. 3B are views illustrating the principles of destructive interference and constructive interference, respectively.

[0043] As in the Fig. 1 and Fig. 2, in the transparent display device according to the first embodiment of the present invention, a pixel including an emission portion E and a transmission portion T is formed in Fig. 2, is repeated two-dimensionally in horizontal and vertical lines in an active region AA of a substrate 100.

[0044] The substrate 100 is formed of a transparent material sufficient to transmit light through its back surface, such as a glass substrate or a transparent plastic film. Although the substrate 100 is formed of a transparent plastic film, a thin glass substrate may be used as the substrate 100 if the transparent display device requires flexibility during use or durability.

[0045] The emitting section E and the transmitting section T are provided in each pixel. The emitting section E may include a plurality of sub-pixels, wherein the respective sub-pixels may include light-emitting layers that emit light of different colors. An arrangement of the sub-pixels provided in the emitting section E may include, for example, red, green, and blue sub-pixels, but is not limited to them. It may further include a white sub-pixel in addition to the red, green, and blue sub-pixels, or may be replaced by another arrangement including, for example, cyan, magenta, and yellow sub-pixels, or by yet another arrangement including a combination of other colored sub-pixels. The light-emitting diodes in the emitting section E may be organic light-emitting diodes (OLEDs) or inorganic light-emitting diodes according to the components of the light-emitting layers.

[0046] Although a case where organic light-emitting diodes are used is described below, the emitting section E can contain, for example, quantum dot light-emitting diodes (QLEDs) by replacing the organic light-emitting layers with layers containing quantum dot light-emitting layers.

[0047] If the emission section E contains organic light-emitting diodes OLED, the organic light-emitting diode OLED contains an organic light-emitting layer 132a, 132b or 132c throughout the pixels above the substrate 100, a reflective electrode structure 111 arranged between a first surface of the organic light-emitting layer 132a, 132b or 132c, ie, the underside of the organic light-emitting layer 132a, 132b or 132c according to Fig.2 and the substrate 100, and a transmissive electrode 140 disposed above a second surface of the organic light-emitting layer 132a, 132b or 132c, ie, the top surface of the organic light-emitting layer 132a, 132b or 132c according to Fig.2 is provided. Furthermore, a first common hole injection and transport layer 131 is provided between the reflective electrode structures 111 and the organic light-emitting layers 132a, 132b, and 132c, and second and third common electron transport and injection layers 133 and 134 are provided between the organic light-emitting layers 132a, 132b, and 132c and the transmissive electrode 140. If circumstances require, the third common layer 134 may be omitted, and the second common layer 133 may be provided as a single common layer between the organic light-emitting layers 132a, 132b, and 132c and the transmissive electrode 140.

[0048] The reflective electrode structure 111 may include at least one reflective electrode and may further include a transparent electrode provided above and / or below the reflective electrode, as required by the circumstances. The transparent display device according to the present invention includes the reflective electrode structures 111 only in the emission section E, wherein the reflective electrode structures 111 function to reflect the light emitted downward from the organic light-emitting layers 132a, 132b, and 132c and thus return the light upward.

[0049] The reflective electrode structures 111 in the emission section E are separated from each other, and the respective reflective electrode structures 111 can define the sub-pixels. At least one thin-film transistor TFT1, TFT2, or TFT3 can be provided in each sub-pixel. The thin-film transistors TFT1, TFT2, and TFT3 are each connected to the reflective electrode structures 111 in the corresponding sub-pixels.

[0050] The first to third common layers 131, 133 and 134 and the transmitting electrode 140 are formed not only over the emitting portions E but also over the transmitting portions T in sequence.

[0051] A light-emitting device includes the elements from the reflective electrode structure 111 to the transmissive electrode 140 in the emission section E. In particular, if the organic light-emitting layer 132a, 132b, or 132c is used as a light-emitting layer, the light-emitting device is referred to as an organic light-emitting diode (OLED). The tests and comparison of the characteristics described below are based on organic light-emitting diodes. However, the transparent display device according to the present invention is not limited to organic light-emitting diodes and can be applied to quantum dot light-emitting diodes that include quantum dot light-emitting layers as the light-emitting layers.

[0052] In the emission section E of the present invention, the thin film transistors TFT1, TFT2 and TFT3 conductively connected to the respective reflective electrode structures 111 are provided, wherein the organic light-emitting diodes OLED formed in the vertical direction and connected to the thin film transistors TFT1, TFT2 and TFT3 are selectively driven by turning on and off the thin film transistors TFT1, TFT2 and TFT3.

[0053] In the transmission portion T where the back side of the substrate 100 is seen, the thin film transistors TFT1, TFT2, and TFT3, the reflective electrodes 111, and the organic light-emitting layers 132a, 132b, and 132c provided in the emission portion E are not provided in the transmission portion T to ensure the transparency of the transmission portion T. Here, the first to third common layers 131, 133, and 134, which are commonly provided in the emission portion E and the transmission portion T, form an organic stack EL having transparency, and the light from the substrate 100 is transmitted through the organic stack EL.

[0054] In the transparent display device according to the first embodiment of the present invention, the transmissive electrode 140 is shared by the emitting portion E and the transmitting portion T. This means that a single transmissive electrode 140, to which a common voltage or ground voltage is applied, is formed throughout the active region containing a plurality of pixels in which an image is displayed. If the transmissive electrode 140 is selectively removed from the surface of the transmitting portion T, the resistance around a portion of the transmitting portion T from which the transmissive electrode 140 is removed is increased, and consequently, a voltage drop of the transmissive electrode 140 may occur. Therefore, the transmissive electrode 140 may be commonly formed in the emitting portion E and the transmitting portion T.

[0055] The transmissive electrode 140 is formed of a silver alloy (Ag alloy), such as MgAg, to have the light transmission properties of the transmission portion T and the resonance properties of the emission portion E, and thus can have both reflection and transmission properties. Otherwise, the transmissive electrode 140 can be a transparent electrode formed of IZO or ITO. If the transmissive electrode 140 is formed of a metal having both reflection and transmission properties, the thickness of the transmissive electrode 140 is 10.0 nm or less, so that the transmission portion T has a transmittance of a certain value or more due to the properties of the transmissive electrode 140 arranged together.

[0056] Further, the transparent display device according to the first embodiment of the present invention includes a cover structure 170 including a first cover layer 171 in contact with the upper surface of the transmissive electrode 140 and having destructive interference properties and a first refractive index n1 of 2.0 or greater, and a second cover layer 172 in contact with the upper surface of the first cover layer 171 and having a second refractive index n2 that is smaller than the first refractive index n1 by 0.2 or more but less than 1.2.

[0057] Here, the first refractive index n1 can be 2.0 to 2.7, while the second refractive index n2 can be 1.3 to 2.0. The first cover layer 171 can have a higher refractive index than the second cover layer 172.

[0058] In the transparent display device according to the present invention, the cap structure 170 is provided to protect the organic light-emitting diodes (OLEDs), assist in the extraction of light in the emission portion E, and increase the transmittance of the transmission portion T. For this purpose, the cap structure 170 is formed by stacking cap layers having different refractive indices, that is, the first cap layer 171 having a high refractive index and the second cap layer 172 having a low refractive index, and thus, by adjusting the respective optical path lengths nd of the first and second cap layers 171 and 172, it has the destructive interference properties similar to the anti-reflection properties when the light from the organic light-emitting diode (OLED) passes through the cap structure 170.In particular, the anti-reflection properties mean that, assuming that a quantity of light L transmitted through the substrate 100 and the organic stack EL in the transmission portion T is 1, a quantity of light R reflected by the cap structure 170 is almost close to 0, so that a quantity of light 1 - R finally emitted from the cap structure 170 becomes a value close to 1, and consequently, there is no loss of light transmitted through the substrate 100 and the organic stack EL, thereby increasing the transmittance.

[0059] In the same manner as the above-described first to third common layers 131, 133, and 134 and the permeable electrode 140, the capping structure 170 is integrally formed throughout the active region AA. The first to third common layers 131, 133, and 134, the permeable electrode 140, and the capping structure 170 may be formed such that their respective areas gradually increase in the upward direction so as to overlap their lower layers, respectively. The permeable electrode 140 may have a protrusion extending from the active region AA (a region extending within a dotted line after Fig.1), wherein the protrusion may be connected to a wiring layer formed above a thin-film transistor array located beneath the transmissive electrode 140 and thus capable of receiving a common voltage or ground signal. In this case, the capping structure 170 may be provided to overlie the entirety of the transmissive electrode 140 and protrude to a portion of the outer side of the active region AA.

[0060] In the cover structure 170, the first cover layer 171 and the second cover layer 172 can be formed from an organic or an inorganic substance, or from an organic-inorganic composite material. The factors determining the properties of the first cover layer 171 and the second cover layer 172 are the refractive indices of the substances constituting the first cover layer 171 and the second cover layer 172, and the optical path lengths nd of the first cover layer 171 and the second cover layer 172, which are determined by the thicknesses of the respective layers.A difference between the optical path length of the first cladding layer 171 and the optical path length of the second cladding layer 172 is within 10% of the optical path length of the first cladding layer 171, and the first and second cladding layers 171 and 172 thus have the properties of destructive interference with respect to the wavelengths of similar ranges or the same range.

[0061] The Fig. 3A and Fig. 3B are views illustrating the principles of destructive interference and constructive interference that occur due to the transmission and reflection properties of light when the light L passing through a first layer having a refractive index na passes through second and third layers having refractive indices nb and nc different from the refractive index na.

[0062] Here, the light L impinges on different interfaces in one direction of propagation and generates different reflected waves at the respective interfaces. The destructive interference according to Fig.3A occurs because a reflected wave RW1 generated by the light propagating from the first layer (with the first refractive index na) to the second layer (with the second refractive index nb) and a reflected wave RW2 generated by the light propagating from the second layer (with the second refractive index nb) to the third layer (with the third refractive index nc) have opposite phases.Here, if the respective reflected waves RW1 and RW2 have the same amplitude and the same period, the sum of the two reflected waves RW1 and RW2 becomes 0 (the reflected waves RW1 and RW2 cancel each other), whereby, while the light L passes through the first layer (with the first refractive index na), the second layer (with the second refractive index nb) and the third layer (with the third refractive index nc), the entire amount of light L is transmitted through the first to third layers without any reflection at the respective interfaces in the propagation direction.

[0063] On the other hand, constructive interference occurs after Fig.3B occurs because the reflected wave RW1 generated by the light propagating from the first layer (with the first refractive index na) to the second layer (with the second refractive index nb) and a reflected wave RW3 generated by the light propagating from the second layer (with the second refractive index nb) to the third layer (with the third refractive index nc) have the same phase. Here, if the respective reflected waves RW1 and RW3 have the same amplitude and the same period, the sum of the two reflected waves RW1 and RW3 has an amplitude twice the amplitude of the single reflected wave RW1, and thus, an amount of reflection of the waves RW1 and RW3 is increased compared to the single reflected wave RW1.If the amplitudes and periods of the respective reflected waves RW1 and RW3 at the interface between the first layer and the second layer and at the interface between the second layer and the third layer are theoretically equal, the light R reflected by the respective interfaces returns to the first layer, and consequently there is no light transmitted through the third layer in a light propagation direction.

[0064] The cover structure 170 of the present invention is arranged to be in contact with the permeable electrode 140 and causes the Fig.3A shows the destructive interference when light from below the cover structure 170 passes through the cover structure 170. Here, the organic light-emitting diode OLED corresponds to the first layer (with the first refractive index na), the cover structure 170 corresponds to the second layer (with the second refractive index nb), and the outer side of the cover structure 170 corresponds to the third layer (with the third refractive index nc).

[0065] Fig. 4 is a schematic view illustrating the transmittance and reflectance characteristics at the cover layers and their interfaces in the transparent display device according to the present invention.

[0066] Fig. Fig. 4 illustrates the transmission portion of the transparent display device according to the present invention shown in Fig.2, wherein the transmissive electrode 140 and the capping structure 170 are stacked on the organic stack EL in the transmission portion of the transparent display device according to the present invention, as shown in Fig.4. In some cases, an additional layer having a similar refractive index to the organic stack EL or the capping structure 170 may be further included between the transmissive electrode 140 and the capping structure 170. The organic stack EL includes an organic light-emitting layer provided therein, wherein an upstream electromagnetic wave UEo and a downstream electromagnetic wave DEo are generated by the organic light-emitting layer.The upward electromagnetic wave UEo is split into an electromagnetic wave 1ET transmitted upward through the transmissive electrode 140 and an electromagnetic wave 1ER reflected downward by the transmissive electrode 140, generating an electromagnetic wave HER reflected by the interface between the first cover layer 171 and the second cover layer 172 of the cover structure 170 and an electromagnetic wave LER reflected downward by the surface of the second cover layer 172. Because the transmittance of the electromagnetic wave 1ET transmitted upward through the transmissive electrode 140 is limited by the amount of light reflected downward, the amount of electromagnetic wave finally transmitted through the cover structure 170 is 1ET - (LER + HER).

[0067] That is, the first cladding layer 171 has a first thickness d1 and a first refractive index n1, wherein a first optical path length n1d1 of the first cladding layer 171 has a value of mλ / 2cosθ by a conditional equation of destructive interference (where m is an integer, λ is a wavelength of destructive interference, and θ is an angle of incidence).

[0068] Furthermore, the second cladding layer 172, which is located above the first cladding layer 171 of the cladding structure 170, has a second thickness d2 and a second refractive index n2, and a second optical path length n2d2 of the second cladding layer 172 is the same as the first optical path length n1d1 of the first cladding layer 171, or 0.9 to 1.1 times the first optical path length n1d1 of the first cladding layer 171, such that a difference therebetween is within 10%. Therefore, the second cladding layer 172 has an optical path length that is the same as or similar to that of the first cladding layer 171, satisfying the condition of destructive interference in the same way as the first cladding layer 171 or in a similar way to the first cladding layer 171.

[0069] Here, according to the destructive interference conditional equation, the first optical path length n1d1 of the first cladding layer 171 and the second optical path length n2d2 of the second cladding layer 172 each have a value of mλ / 2cosθ (where m is an integer, λ is a wavelength of destructive interference, and θ is an angle of incidence), or a value of 0.9 to 1.1 times mλ / 2cosθ. Here, a wavelength λ of the primary destructive interference is a short wavelength in the visible wavelength range, that is, a blue wavelength. By varying the value of m in the destructive interference conditional equation "2ndcosθ = mλ", a green or a red wavelength range in addition to the blue wavelength range can satisfy the destructive interference conditional equation.

[0070] In the present invention, the reason why the wavelength λ of the primary destructive interference is the blue wavelength is to compensate for the transmittance uniformity in the blue wavelength, which is the worst in a single-layer structure. A peak wavelength of the destructive interference wavelength may be in the range of approximately 430 nm to 465 nm.

[0071] In the present invention, the cover structure 170 has the characteristics of destructive interference, thereby canceling the reflected waves of the respective interfaces to increase an amount of transmittance of the finally emitted light and thus improving the transmittance, and is implemented as a stacked structure of the first cover layer 171 having a high refractive index and the second cover layer 172 having a low refractive index to obtain uniform transmission characteristics according to color regardless of the wavelength change in the visible wavelength range.

[0072] Fig. Figure 5 is a graphical representation showing the permeabilities of different deck structures, and Fig. Figure 6 is a graph showing the intensities of blue light emitted by the respective cover structures.

[0073] When a single cover layer of HRCPL CI with a high refractive index (HR) and with the properties of constructive interference (CI) is used, there is a tendency for the transmittance to be increased in a direction from a short wavelength to a long wavelength in the visible wavelength range from 400 nm to 650 nm, as shown in Fig. 5 is shown.

[0074] Furthermore, when a single coating layer of HRCPL DI having a high refractive index (HR) and destructive interference (DI) characteristics is used, there is a tendency that the transmittance is increased by 45% or more in a wavelength range from 400 nm to 520 nm, and then decreased in a wavelength range from 520 nm to a long wavelength.

[0075] On the other hand, when a stacked structure including the first cover layer 171 having a high refractive index and exhibiting destructive interference (DI) characteristics and the second cover layer 172 having a low refractive index, that is, the cover structure 170 of the transparent display device according to the present invention is used, the transmittance tends to be uniformly maintained at 90% or more at least in the visible wavelength range of 400 nm to 650 nm.That is, the transparent display device according to the present invention exhibits a primary effect of improving the transmittance by a principle of increasing the amount of emitted light by controlling the refractive index profiling at the interface between the cap layer 171 having a high refractive index and the cap layer 172 having a low refractive index and the interface between the cap layer 171 having a high refractive index and the organic light-emitting diode OLED as in the effect of destructive interference. Fig.3A. Furthermore, by preventing a change in the transmittance according to the wavelength output when the destructive interference or the constructive interference is separately applied by the double-layered cover structure 170, the transparent display device according to the present invention has a secondary effect of maintaining uniform transmittance according to the wavelength, particularly in the visible wavelength region.

[0076] That is, in the single capping layers HRCPL DI and HRCPL CI according to the experimental examples, the transmittance is increased or decreased as the wavelength increases, but in the capping layer structure 170 of the transparent display device according to the present invention, the transmittance is maintained uniformly regardless of the wavelength in the visible wavelength range. If the single capping layer is used, the transmittance is increased or decreased in the visible wavelength range. If the single capping layer HRCPL CI with constructive interference properties is used, the transmittance tends to be increased in a longer wavelength range rather than in the visible wavelength range, and thus the transmittance in the visible wavelength range is comparatively low.Furthermore, if the single coating layer HRCPL DI having the destructive interference properties is used, the transmittance in the visible wavelength region is high, but a transmittance of light in the visible wavelength region is increased and decreased, and thus, when the single coating layer HRCPL DI is applied to a light-emitting display device, the luminance in the green wavelength region is relatively high and thus serves as a factor that hinders user visibility.The transparent display device according to the present invention reduces the optical path lengths of two interfaces and a difference in the optical path length, and thus enables uniform transmittance in a direction from a short wavelength to a long wavelength in the visible wavelength range of 450 nm to 650 nm, thereby achieving a stable display without a luminance difference of a specific color in the visible wavelength range.

[0077] In Fig.6, it can be confirmed that when the single cap layer HRCPL DI with a high refractive index and destructive interference properties is used, the peak wavelength intensity is about 0.21, which is lower than the peak wavelength intensity, i.e., 0.26, when the single cap layer HRCPL CI with a high refractive index and constructive interference properties is used. This means that when the single cap layer HRCPL DI with a high refractive index and destructive interference properties is used, the transmission properties are improved in all wavelength ranges, but the microcavity effect in the organic light-emitting device is reduced, i.e., weak cavity properties are presented, and the pure blue efficiency is reduced.Furthermore, it can be seen that when the single cap layer HRCPL DI with a high refractive index and with the properties of destructive interference is used, a shoulder of the spectrum appears at a wavelength of about 490 nm, the concentration of the peak wavelength is reduced, and consequently the color purity is reduced.

[0078] On the other hand, it can be confirmed that when the single cladding layer HRCPL CI having a high refractive index and having the constructive interference characteristics is used or the two-layer cladding structure 170 including the first and second cladding layers 171 and 172 according to the present invention is used, the peak wavelength appears at about 450 nm to 460 nm, the intensity of the peak wavelength is about 0.235 or greater, so that an amount of light reflected by the interface between the cladding layers 171 and 172 is reduced and thus an amount of emitted light is increased, and no shoulder appears at other wavelengths in the spectrum when blue light is emitted, thus the color purity is high.

[0079] In Fig.6, the color purity is excellent when the single cover layer HRCPL CI with a high refractive index and with the properties of constructive interference is used, but as above (with respect to Fig. 5), the transmittance of the single HRCPL CI cover layer with a high refractive index and with the properties of constructive interference is less than 90% anywhere in the visible wavelength range, a deviation of the transmittance in the visible wavelength range is large and consequently the uniformity of the color efficiency according to the wavelength cannot be ensured.

[0080] That is, if a single cover layer, that is, the single cover layer HRCPL CI having a high refractive index and having the properties of constructive interference or the single cover layer HRCPL DI having a high refractive index and having the properties of destructive interference is used, the deviation of the transmittance in the visible wavelength range is large, and consequently the white light is observed as light of a color with relatively high transmittance even if the transparent display device is implemented to emit white light.The cladding structure 170 according to the present invention, in which the first cladding layer 171 having a high refractive index and the second cladding layer 172 having a low refractive index have the properties of destructive interference, enables the transmittance to be uniform throughout the visible wavelength range and thus solves the above-described problem caused by the single cladding layer.

[0081] The following describes the structures of transparent display devices according to various experimental examples and their test results in comparison with the transparent display device according to the present invention.

[0082] The Fig.7A to 7C are cross-sectional views illustrating transparent display devices according to various experimental examples according to the arrangement of a second electrode arranged in a light emission direction and a cover structure, and Fig. Figure 8 is a graph showing the transmittances of the transparent display devices according to the Fig. 7A to 7C.

[0083] As in Fig. 7A, includes a transparent display device A [PO reference] (in Fig.8) According to a first experimental example, sub-pixels configured to emit light of different colors and a transmission portion in each pixel are provided above a substrate 10, thin-film transistors TFT1, TFT2, and TFT3 provided in the respective sub-pixels, and organic light-emitting diodes (OLEDs) connected to the thin-film transistors TFT1, TFT2, and TFT3. The organic light-emitting diode (OLED) includes a first electrode 11 and a second electrode 40 arranged opposite each other, and a plurality of organic layers 31, 32a / 32b / 32c, 33, and 34 provided between the first and second electrodes 11 and 40.In the first experimental example, the second electrode 40 is a transparent electrode formed of a transparent oxide such as ITO or IZO. The interface matching with an organic layer directly in contact with the second electrode 40 is poor, and thus a buffer layer 39 is further provided. As the organic layers, a first common hole-transport layer 31, an organic light-emitting layer 32a, 32b, or 32c, a second common electron-transport layer 33, and a third common electron-injection layer 34 are provided in sequence. The first to third common layers 31, 33, and 34 and the second electrode 40 are provided together in the emission portions and the transmission portions, and a cap layer 50 provided over the organic light-emitting diodes (OLEDs) is provided as a single cap layer having destructive interference characteristics.

[0084] The transparent display device according to the first experimental example is an example of a transparent display device at an initial stage, wherein, in a structure having both emission portions and transmission portions, the transmission properties of the transmission portions are further emphasized, for which purpose, the second electrode 40 is provided as the transparent electrode. Here, because the microcavity effect at the red, green, and blue wavelengths in the organic light-emitting diode (OLED) is reduced (weak cavity properties), the emission portion has a transmittance of less than 75% in the visible wavelength range, as shown in Fig. 8, the color efficiency in the emission section is poor regardless of the interference properties of the single cover layer 50.

[0085] As in Fig.7B, a transparent display device B [CPL destructive interference] (in Fig.8) According to a second experimental example, from the transparent display device A [PO reference] according to the first experimental example, a second electrode 60 is formed of a metal or metal alloy having excellent interface matching with a third common layer 34, and a buffer layer is omitted, so that the third common layer 34 and the second electrode 60 are in direct contact with each other. In this case, the second electrode 60 formed of a metal component has a thickness of 14.0 nm or greater to exhibit a sufficient microcavity effect in an emission portion. Here, a cap layer 50 located over the second electrode 60 is provided as a single cap layer having destructive interference properties to enhance the light extraction effect.In this case, in the transparent display device according to the second experimental example, the transmittances of red light, green light, and blue light are improved overall due to the increase in the efficiency of the emission portion, but fluctuations in transmittance are caused according to the wavelength change. Because the second electrode 60 formed of a transflective metal has a thickness of 14.0 nm or greater, the transmittance of a transmission portion is reduced.

[0086] In order to improve the transmittance of the transmission portion of the transparent display device according to the second experimental example, a transparent display device including a second electrode 70 having a reduced thickness is proposed according to a third experimental example. Fig. Figure 7C illustrates the transparent display device C [CPL constructive interference] (in Fig.8) according to the third experimental example, in which case a cover layer 80 located over the second electrode 70 is provided as a single cover layer having constructive interference properties to increase the transmittance. In the transparent display device according to the third experimental example, the second electrode 70 is formed of a metal or a metal alloy and has a thickness of 10.0 nm or less. The transmittance in the visible wavelength range is increased due to the cover layer 80 having constructive interference properties located over the second electrode 70, but is greatly changed by about 30%, particularly in the blue wavelength range from 400 nm to 490 nm. The transmittance is not uniform in other wavelength ranges and is further reduced in the wavelength range from about 490 nm to 510 nm or more, as shown in Fig.8. That is, the transparent display device according to the third experimental example achieves a transmittance of a certain degree or more through the second electrode 70 with a small thickness, but has uneven transmittance in the visible wavelength range and thus has different color efficiencies of blue, green, and red, thereby causing difficulty in uniform and stable color expression.

[0087] Specifically, when comparing the transparent display devices according to the second and third experimental examples, it was observed that, as a result of measuring a CIEy value of the color coordinates, the CIEy value changed from 0.055 to 0.102. This means that the color deviation of blue in the transparent display device according to the third experimental example is large, and consequently, it is difficult to express pure blue.

[0088] Fig. 9 is a schematic cross-sectional view illustrating the transmission and reflection characteristics of the cover layers and their interfaces in the transparent display device according to the third experimental example and the transparent display device according to the present invention.

[0089] In Fig. 9, reference numeral 1st step represents the transmission and reflection characteristics of the respective layers of the transparent display device according to the third experimental example, while reference numeral 2nd step represents the transmission and reflection characteristics of the respective layers of the transparent display device according to the present invention.

[0090] In the third experimental example and the present invention, the second electrode and a semi-transparent electrode 140 are formed of a semi-transparent metal, i.e., a silver alloy such as Ag:Mg. The thicknesses of the second electrode and the semi-transparent electrode 140 are 10.0 nm or less and 5.0 nm or more, respectively, to prevent an increase in resistance throughout their regions. This serves to increase the transmittance in the transmission portion.

[0091] To illustrate the transmission and reflection characteristics, the transmittances of the upwardly emitted light are compared when the second electrode and the semi-transparent electrode 140 having the same thickness are applied to the transparent display device according to the third experimental example and the transparent display device according to the present invention.

[0092] In the transparent display device according to the third experimental example, the second electrode 140 (70 in Fig. 7C) and the single cap layer 80 with a high refractive index are stacked sequentially above the organic stack EL. The organic stack EL includes an organic light-emitting layer provided therein, wherein an upward electromagnetic wave UEo and a downward electromagnetic wave DEo are generated by the organic light-emitting layer. From the upward electromagnetic wave UEo, an electromagnetic wave 1ET and an electromagnetic wave 1ER are generated, which are transmitted upward and reflected downward by the second electrode 140, respectively, and an electromagnetic wave 2ET and an electromagnetic wave 2ER are generated, which are transmitted upward and reflected downward by the upper surface of the cap layer 80, respectively.

[0093] In the transparent display device according to the present invention, the organic stack EL includes an organic light-emitting layer provided therein, wherein an upward electromagnetic wave UEo and a downward electromagnetic wave DEo are generated by the organic light-emitting layer, an electromagnetic wave 1ET and an electromagnetic wave 1ER, which are transmitted upward and reflected downward by the second electrode 140, respectively, are generated from the upward electromagnetic wave UEo, and an electromagnetic wave HER, which is reflected by the interface between the first cap layer 171 and the second cap layer 172 of the cap structure 170, and an electromagnetic wave LER, which is reflected downward by the surface of the second cap layer 172, are generated, as described above with respect to Fig. 4 has been described.

[0094] Assuming that the total amount of the electromagnetic wave 1ET upwardly transmitted through the second electrode (or the transmissive electrode) 140 commonly provided in the transparent display devices according to the third experimental example and the present invention is 1, a value obtained by subtracting the reflectance (an amount of the electromagnetic wave reflected by the cover layer 80 or the cover structure 170 disposed thereon) from the total amount of the electromagnetic wave 1ET is an amount of light actually upwardly transmitted through the cover layer 80 or the cover structure 170.

[0095] The reflectance of the transparent display device according to the third experimental example corresponds to the electromagnetic wave 2ER reflected downward by the upper surface of the single cover layer 80, that is, monoreflection occurs. The reflectance of the transparent display device according to the present invention corresponds to the reflectance of the cover structure 170 including the first and second cover layers 171 and 172 provided above the second electrode 140, that is, the sum of the electromagnetic wave LER reflected downward by the surface of the second cover layer 172 and the electromagnetic wave HER reflected by the interface between the first and second cover layers 171 and 172, (LER + HER).

[0096] For example, assuming that the first refractive index of the first cover layer 171 and the single cover layer 80 with a high refractive index is 2.25, the second refractive index of the second cover layer 172 is 1.5, and a structure located above the cover layer 80 and the cover layer 170 is air, the reflectances of the transparent display devices according to the third experimental example and the present invention are compared below.

[0097] For reference, the reflectance of the interface between two layers with different refractive indices n1 and n2 (n1 cosθi−n2 cosθtn1 cosθi+n2 cosθt)2 (where θi is an angle of incidence and θt is an angle of exit).

[0098] Considering an angle of incidence and an angle of exit of the respective layers in the normal direction where the visibility in front is most effective, the angle of incidence θi and the angle of exit θt can be 0°.

[0099] Because in the transparent display device according to the third experimental example, only the monoreflection (2ER) by the top surface of the single cover layer 80 is considered, when the refractive index of the cover layer 80, i.e., 2.25, and the refractive index of air, i.e., 1, are substituted into the above equation, a reflectance of about 15% is calculated.

[0100] In the transparent display device according to the present invention, the reflectance of the interface between the first and second cover layers 171 and 172 by reflection (HER) is calculated as 4% because the refractive indices of the first and second cover layers 171 and 172 are 2.25 and 1.5, and the reflectance of the upper surface of the second cover layer 172 by reflection (LER) by the upper surface of the second cover layer 172 is calculated as 4% assuming that there is air above the second cover layer 172 because the refractive index of air is 1. That is, even if there are two interfaces, a difference between the reflectance of the two interfaces becomes 0%.As another example, if the refractive index of the first cladding layer 171 is 2.0, the refractive index of the second cladding layer 172 is 1.5, and there is air above the second cladding layer 172, the interface between the first and second cladding layers 171 and 172 has a reflectance of about 2.8%, while the interface between the second cladding layer 172 and the air has a reflectance of 4%, thus a difference between them is within 2%.

[0101] That is, in the transparent display device according to the present invention, a plurality of interfaces at which reflection occurs in the propagation direction of light are formed by the cover structure 170, a refractive index difference between two layers constituting each of the interfaces is reduced, and thus, the reflectance can be greatly reduced in proportion to the square of the refractive index difference, and an amount of light reflected downward by the upper surface of the cover structure 170 is reduced compared with the transparent display device with a high transmittance according to the third experimental example (2ER > (LER + HER)), thus the transmittance can be increased due to the anti-reflection effect.

[0102] Although the example described above illustrates that there is air outside the cover layer 80 and the cover structure 170, in the transparent display device according to the present invention, the case can be considered that an encapsulation layer (see 300 Fig. 15) of a filling material and a structure corresponding to an upper substrate are located above the cover structure 170.

[0103] Assuming that the refractive index of the encapsulation layer of the filler material located above the cover structure 170 is nEncap, here the reflectance of the top surface of the second cover layer 172 corresponds to (n2 cosθi−nEncap cosθtn2 cosθi+nEncap cosθt)2 (where nEncap is the refractive index of an element located above the second cap layer, θi is an angle of incidence, and θt is an angle of exit).

[0104] The reflectance of the interface between the first cover layer 171 and the second cover layer 172 is (n1 cosθi−n2 cosθtn1 cosθi+n2 cosθt)2 (where θi is an incident angle and θt is an exit angle), wherein a difference between the reflectance of the interface between the first and second cover layers 171 and 172 and the reflectance of the upper surface of the second cover layer 172 is set to 5% or less, so that the transparent display device according to the present invention has the effect of increasing the transmittance. Because, if the reflectance of one interface in the light emission direction is better than the reflectance of the other surface, it is suitable for the display device formed by stacking the cover layer 171 with a high refractive index and the cover layer 172 with a low refractive index, which are arranged in Fig.5, formed cover structure is difficult to obtain uniform transmission characteristics according to the wavelength, the reflectance difference between the two interfaces is minimized.

[0105] Because the cover layer 170 in the transparent display device according to the present invention needs to have the properties of destructive interference to achieve transmittance, the first thickness may be 30.0 nm to 50.0 nm, while the second thickness may be 30.0 nm to 70.0 nm.

[0106] The first cover layer 171 and the second cover layer 172 follow the destructive interference condition equation "2ndcosθ = mλ," whereby the optical path lengths of the respective layers 171 and 172 are equal or have a difference within 10%. Here, in the destructive interference condition equation, a wavelength of destructive interference λ is a blue wavelength of approximately 430 nm to 465 nm to maintain high transmittance. Considering front-side visibility, θ can be 0°.

[0107] Because the second cladding layer 172 has a relatively low refractive index n2 (n2 < n1), the second thickness d2 of the second cladding layer 172 may be greater than the first thickness d1 of the first cladding layer 171 to set a difference in optical path lengths (n1d1 - n2d2) with the first cladding layer 171 having a relatively high refractive index n1 to be within 10% of the optical path length n1d1 of the first cladding layer 171.

[0108] Because the encapsulation layer located above the capping structure 170 includes multiple layers to have an encapsulation function and has a thickness of 1 μm or greater, light transmitted from below can be transmitted through the encapsulation layer without reflection at the interface with the capping structure 170 regardless of a refractive index difference with the capping structure 170.

[0109] The encapsulation layer may have a structure in which an inorganic film that can be deposited at a low temperature, such as SiNx, SiONy, SiOx, silicon oxycarbide (SiOC), or Al2O3, and an organic film formed of a non-photosensitive organic insulating material such as PCL, acrylic resin, epoxy resin, polyimide, polyethylene, or a photosensitive organic insulating material such as photoacyl, are alternately stacked. The filler may contain a resin such as epoxy resin, acrylic resin, polyimide, or polyethylene, and may contain a moisture absorber in addition to the resin.

[0110] The following describes the reasons for using the two-layer cover structure 170 in the present invention.

[0111] In the transparent display device according to the present invention, the destructive interference characteristics of the cover structure 170 depend on the first cover layer 171 closest to the transmissive electrode 140, and in particular, the first cover layer 171 has a high refractive index of 2.0 or more and a very small thickness of 30.0 nm to 50.0 nm. In the case of a material with a small thickness and a high refractive index, the intensity of blue light is low, and the transmittance tends to decrease as the wavelength is increased in the visible wavelength range, as shown in the corresponding curves representing the destructive interference (DI) characteristics in the Fig. 5 and Fig.6. Therefore, in the transparent display device according to the present invention, the second clad layer 172 having a lower refractive index than the first clad layer 171 is stacked over the first clad layer 171 to uniformly maintain the transmittance characteristics in the visible wavelength region regardless of the wavelength. Because, among materials having a low refractive index, a material whose transmittance hardly changes according to the wavelength can be used, the material can satisfy the optimal condition for achieving uniform transmittance according to the wavelength. Furthermore, because the interface reflection is reduced as the wavelength is increased, the transmittance can be increased in a long wavelength region.

[0112] The Fig.10A to 10C are graphs showing the transmittance trends of blue light, green light, and red light according to the application of the thicknesses of the respective coating layers of the coating structure of the transparent display device according to the present invention.

[0113] In order to enable the first and second cover layers 171 and 172 to have the same or similar destructive interference properties in the transparent display device according to the present invention, the optical path length of the second cover layer 172 is 0.9 to 1.1 times the optical path length of the first cover layer 171.In the cap structure 170 having the same thickness throughout the active region AA, as the results of measuring the transmittance of blue light, green light, and red light according to the change in the thicknesses of the first cap layer 171 and the second cap layer 172, it can be confirmed that when the thickness of the first cap layer 171 is about 25.0 nm to 50.0 nm and the thickness of the second cap layer 172 is about 30.0 nm to 70.0 nm, the cap layer structure 170 has a blue light transmittance of 0.860, a green light transmittance of 0.86 or more, and a red light transmittance of 0.87 or more, and thus collectively has high transmittances of 0.86 or more with respect to various wavelengths.That is, it can be confirmed that if the cover structure 170 including the first and second cover layers 171 and 172 having different refractive indices is used according to the present invention to have the destructive interference characteristics, the cover structure 170 has uniformly high transmittances with respect to the wavelengths in the visible wavelength range if the first and second cover layers 171 and 172 are within the thickness ranges described above.

[0114] The Fig. 11A and Fig. 11B are graphs showing the transmittances and spectra in the test examples in which a cap layer with a high refractive index is used as a single cap layer, but the cap layer with a high refractive index is set to have different destructive interference characteristics and constructive interference characteristics.

[0115] In a test conducted in Fig. As shown in Figure 11A, the single cladding layer with a high refractive index of 2.2 according to the third experimental example was used together, a first test example (HRCPL DI) in which the thickness of the cladding layer was adjusted to exhibit destructive interference characteristics, a second test example (HRCPL DI < t < CI) in which the thickness of the cladding layer was adjusted to exhibit characteristics between destructive interference and constructive interference, and a third test example (HRCPL CI) in which the thickness of the cladding layer was adjusted to exhibit constructive interference characteristics were prepared, and the transmittances of the cladding layers of the first, second, and third test examples were measured according to wavelength. As shown in Fig.11A, the cover layer of the first test example showed high transmittance in the blue wavelength range from about 460 nm to 520 nm, the cover layer of the second test example showed high transmittance in the green wavelength range from about 520 nm to 590 nm, and the cover layer of the third test example showed high transmittance in the red wavelength range from about 620 nm to 630 nm. However, it can be confirmed that even in each of the first to third test examples, although the characteristics of the single cover layer are varied between destructive interference and constructive interference, it is difficult for the single cover layer to show uniform transmittance throughout the visible wavelength range.That is, it can be confirmed that all the cover layers of the first to third test samples show uneven transmittance in the visible wavelength range.

[0116] In a Fig.11B, the peak wavelength characteristics of blue light were examined in the first to third test examples, and it can be confirmed that when the single cap layer having a high refractive index and constructive interference characteristics is used, the microcavity effect in an organic light-emitting diode is increased and an intensity of the peak wavelength is increased, while when the destructive interference of the cap layer is increased, the intensity of the peak wavelength is decreased, a shoulder of the spectrum occurs, and consequently, the color distortion of blue light and the CIEy value of the color coordinates of blue light are increased.That is, in the cover layer with the properties of constructive interference of the third test example (HRCPL CI), a CIEy value (By) of the color coordinates is 0.055, in the cover layer with the properties of destructive interference of the first test example (HRCPL DI), a CIEy value (By) of the color coordinates is 0.108, and in the cover layer with the properties between destructive interference and constructive interference of the second test example (HRCPL DI < t < CI), a CIEy value (By) of the color coordinates is 0.094. [Table 1] Test example Condition Optical properties (required luminance) Top layer properties Driver voltage (V) Current density (mA / cm2) ηJ (luminance) (cd / A) CIEx CIEy Transmittance / 460 nm 1. TB HRCPL DI (t0) 8,0 8,4 12,4 (121) 0,137 0,102 94 % 2. TB HRCOL (t1) t0 < t1 < t3 7,9 6,5 11,7 (152) 0,141 0,077 87 % 3. TB HRCPL CI (t3) 7,5 4,9 10,1 (183) 0,141 0,055 79 % 4. TB HRCOL (t2) t1 < t2 < t3 7,6 5,1 11,7 (191) 0,143 0,061 82 %

[0117] From Table 1 above, it can be seen that when the destructive interference characteristics are increased as in the first test example, the transmittance in the blue wavelength region is 94%, but the driving voltage is high and the distortion of the CIEy value of the color coordinates is severe. For reference, in a fourth test example shown in Table 1, the thickness of the cap layer is set to t2, which is larger than the thickness of the cap layer of the second test example, and the cap layer has characteristics between destructive interference and constructive interference. The cap layer of the fourth test example can exhibit the maximum transmittance at a longer wavelength than the cap layer of the second test example. The cap layer of the fourth test example has a thickness between the thickness of the cap layer of the second test example and the thickness of the cap layer of the third test example, and thus has the effects such asthe drive voltage, current density, permeability, etc., which lie somewhere between the effects of the second and third test examples.

[0118] It can be seen that among the first to fourth test examples described above, the third test example, in which the single cover layer with low transmittance and with the characteristics of constructive interference is provided, has the least distortion of the CIEy value of the color coordinates.

[0119] The following describes a test in which a two-layer cover structure including a cover layer with a high refractive index and a cover layer with a low refractive index as in the transparent display device of the present invention was used together, a fifth test example in which the thickness of the first cover layer was adjusted to have the characteristics of destructive interference, and sixth and seventh test examples in which the thickness of the first cover layer was adjusted to have the characteristics between destructive interference and constructive interference were prepared, and the optical characteristics of the fifth, sixth, and seventh test examples were compared with the third test example.

[0120] The Fig. 12A and Fig.12B are graphs illustrating the transmittances and spectra of a capping structure formed by stacking a capping layer with a high refractive index and destructive interference properties and a capping layer with a low refractive index, another capping structure, and a single capping layer with a high refractive index and constructive interference properties. [Table 2] Test example Condition Optical properties (required luminance) Top layer properties Driver voltage (V) Current density (mA / cm2) ηJ (luminance) (cd / A) CIEx CIEy Transmittance / 460 nm 3. TB HRCPL CI (t3) 7,5 4,9 10,1 (183) 0,144 0,055 79 % 5. TB HRCOL DI (t4) / LRCPL 7,6 6,1 10,5 (162) 0,141 0,065 91 % 6. TB HRCPL (t5) / LRCPL (t4 < t5) 7,5 5,7 10,4 (170) 0,141 0,061 86 % 7. TB HRCOL (t6) / LRCPL (t5 < t6) 7,5 5,4 11,1 (182) 0,140 0,061 83 %

[0121] As in the fifth to seventh test examples shown in Table 2, it can be confirmed that when the two-layer cover structures with different refractive index differences between the cover layers are used, the transmittances of all the two-layer cover structures in the blue wavelength range are increased. In particular, it can be confirmed that in the fifth test example, in which the first cover layer exhibits the characteristics of destructive interference, compared to the sixth and seventh test examples in which the first cover layer exhibits the characteristics between destructive interference and constructive interference, the transmittance of the cover structure in the blue wavelength range was increased to 91%, and the cover structure had the highest current density of 6.1 mA / cm2 and a CIEy value of 0.065 of the color coordinates, which is within a color purity range of blue light. As shown in Fig.12A, it can be seen that among the two-layer cover structures, the two-layer cover structure of the fifth test example has a uniform transmittance of 90% or more in the visible wavelength region.

[0122] Furthermore, Fig. 12B that the single cover layer having the constructive interference characteristics of the third test example has excellent light intensity at the wavelength of 460 nm, but, like the transparent display device according to the present invention, the double-layer cover structures of the fifth and sixth test examples do not generate a shoulder in the spectrum presenting peaks at the wavelength of 460 nm and thus maintain CIEy values ​​of 0.065 or less of the color coordinates, so that distortion in the color coordinates hardly occurs.

[0123] The Fig.13A to 13C are graphs showing the spectra of test examples of a single cap layer having destructive interference characteristics, a single cap layer having constructive interference characteristics, and the cap layer structure according to the present invention when blue light, green light, and red light are emitted, respectively. [Table 3] Condition Optical properties (required luminance) Top layer Driver voltage (V) Current density (mA / cm2) ηJ (luminance) (cd / A) CIEx CIEy Permeability Blue (460 nm) 3. TB (CI) 7,5 4,9 10,1 (183) 0,144 0,066 79 % TB (DI) 8,0 8,4 12,4 (121) 0,137 0,102 94 % 5. TB (HRCPL (DI) / LRCPL 7,6 6,1 10,5 (162) 0,141 0,065 91 % Green (520 nm) 3. TB 6,8 3,9 219,4 (789) 0,278 0,683 83 % 1. TB 7,3 6,6 1391 (412) 0,338 0,630 95 % 5. TB 7,0 4,6 187,0 (649) 0,288 0,675 91 % Red (630 nm) 3. TB 6,6 6,8 45,1 0,693 0,305 89 % 1. TB 7,0 10,9 27,8 0,695 0,303 89 % 5. TB 6,5 7,3 41,6 0,694 0,304 90 %

[0124] In Table 3 and the Fig.13A to 13C, it can be seen that when the cap structure formed by stacking the cap layer having a high refractive index and destructive interference properties and the cap layer having a low refractive index according to the present invention (fifth test example) is used, compared to the single cap layer having constructive interference properties (third test example) and the single cap layer having destructive interference properties (first test example), the low driving voltage properties are achieved, the transmittance is much more increased than in the single cap layer having constructive interference properties, in which the color purity is excellent (third test example), and no color distortion occurs at corresponding wavelengths. Furthermore, as shown in FIGS. Fig.13A to 13C, in the single cap layer having destructive interference characteristics (first test example), a shoulder appears at wavelengths other than the emitted wavelength in the respective wavelength ranges, but in the fifth example of the cap structure according to the present invention, no shoulder appears, thus confirming an improvement in the efficiency of each color. That is, when the cap structure according to the present invention is used, the color efficiency can be increased by 30% compared to the cap layer of the third test example, and the correction of color coordinates can be performed compared to the cap layer of the first test example.

[0125] In order to correct the color coordinates, the inventor(s) of the present invention investigated the optical properties of the third test example (the single cap layer having the constructive interference properties), the first test example (the single cap layer having the destructive interference properties), and the fifth test example (the cap structure formed by stacking the cap layer having a high refractive index and having the destructive interference properties and the cap layer having a low refractive index) applied to the present invention by replacing a generally used pyrene-based blue dopant with a boron-based dopant having the deep blue light-emitting properties as a dopant of a blue light-emitting layer used in the organic light-emitting diode provided under the cap layer.

[0126] The boron-based dopant with the properties of emitting deep blue light has a peak wavelength 5 nm or more shorter than the peak wavelength of the pyrene-based blue dopant and a FWHM 10% or more narrower than the FWHM of the pyrene-based blue dopant.

[0127] In the above-described test examples shown in Tables 1 to 3, the pyrene-based blue dopant was used as a dopant of the blue light emission layer, wherein a peak wavelength of the blue light is about 460 nm or longer.

[0128] If the boron-based dopant having the characteristics of emitting deep blue light is used, a peak wavelength of the blue light can be 455 nm or shorter, a FWHM can be about 20 to 30 nm, and thus a deep and narrow emission spectrum can be obtained. [Table 4] Test example Optical properties (required luminance) Driver voltage (V) Current density (mA / cm2) ηJ (luminance) (cd / A) CIEx CIEy Transmittance / 460 nm Transmittance / 520 nm 3. TB 7,8 4,3 12,5 (226) 0,144 0,155 79 % 83 % 1. TB 8,1 8,4 12,2 (123) 0,138 0,099 95 % 95 % 5. TB 7,7 5,6 11,9 (178) 0,141 0,067 91 % 91 %

[0129] As shown in Table 4, which indicates the optical properties of the cap layers and the cap structure according to the present invention when the boron-based dopant having the deep blue light emitting properties is used, it can be seen that the cap structure of the present invention when the boron-based dopant having the deep blue light emitting properties is used has a luminance of 178 cd / A, which is increased by about 10% compared to the luminance (162 cd / A) of the cap structure of the present invention when a generally used pyrene-based dopant (blue in the fifth test example of Table 3) is used.Furthermore, it can be confirmed that the cap structure of the present invention, when the boron-based dopant having the characteristics of emitting deep blue light is used, maintains the transmittances at the blue and green wavelengths at 90% or higher and thus can have uniform and high transmittance in the visible wavelength region without distortion of the color coordinates.

[0130] The cover structure of the present invention may be provided as a three-layer or a four-layer cover structure in addition to the two-layer cover structure described above. If a three-layer or a four-layer cover structure is provided, the three-layer or four-layer cover structure is configured such that the refractive indices of the respective cover layers gradually decrease in the upward direction. Furthermore, the optical path lengths of all the cover layers follow the application of the optical path length at which constructive interference occurs at the blue wavelength when a single cover layer is used, a reflectance difference between the interfaces is maintained within a certain range (e.g., 5% or less), and a difference in the optical path lengths between the cover layers is maintained within a certain range.Because the cover layers of the cover structure each have refractive indices that gradually decrease in the upward direction, the upper cover layers do not have fluctuations in reflectance according to the wavelength characteristics, and thus the three-layer or four-layer cover structure can be converted to the two-layer cover structure HRCPL DI / LRCPL according to the . Fig. 5 and Fig. 6 can have similar optical properties.

[0131] Hereinafter, the transparent display device according to the present invention will be described in detail in connection with an array formed over the array substrate 100.

[0132] Fig. 14 is a plan view illustrating a transparent display device according to a second embodiment of the present invention, and Fig. 15 is a line II' to Fig. 14 taken cross-sectional view.

[0133] In the transparent display device according to the second embodiment of the present invention, the emission sections E are provided to correspond to the intersection points between the scanning lines SL and the data lines DL, while the transmission sections T are provided between adjacent emission sections E.

[0134] Because the pass sections T are intended to be transparent, the pass sections T are arranged so that they do not overlap the wirings SL and DL and the thin-film transistors TFT1 and TFTS.

[0135] In areas other than the emission sections E and the transmission sections T, a bank 150 is formed to overlap the elements requiring light shielding, such as the wirings SL and DL, and to separate adjacent pixel or sub-pixel areas.

[0136] Here, there may be a distance between the emitting section E and the transmitting section T, or there may be no distance therebetween, and if there is no distance between the emitting section E and the transmitting section T, the emitting sections E are formed to overlap the wirings SL and DL, so that the wirings SL and DL located under the organic light-emitting diodes OLED in the emitting sections E are not visible.

[0137] Now, the arrangement of the colors of emitted light in the transparent display device according to the present invention will be described.

[0138] The red sub-pixels RE and the blue sub-pixels BE may be arranged so that the red sub-pixels RE and the blue sub-pixels BE are adjacent to each other in the horizontal direction with the transmission portion T provided therebetween, and the red sub-pixels RE and the green sub-pixels GE may be arranged so that the red sub-pixels RE and the green sub-pixels GE are adjacent to each other in the vertical direction. In the illustrated example, the contribution of green light to the emission of white light is increased by increasing the number of green sub-pixels GE. However, the present invention is not limited to this; the number of red sub-pixels RE or green sub-pixels GE may be increased, or the same number of red sub-pixels RE, green sub-pixels GE, and blue sub-pixels BE may be arranged according to a specific purpose.

[0139] As shown in a region A, a transparent electrode 1200, an organic stack 130' including the first common layer 131, the second common layer 133, and the third common layer 134, and the transmissive electrode 140 are collectively arranged in the transmission portions T. Further, a cap structure 170 formed by stacking a first cap layer 171 having a high refractive index and destructive interference properties and a second cap layer 172 having a low refractive index is provided over the transmissive electrode 140.Because an optical path length n2d2 of the second cladding layer 172 is the same as an optical path length n1d1 of the first cladding layer 171 or is similar to the optical path length n1d1 of the first cladding layer 171 such that a difference therebetween is within 10%, the second cladding layer 172 can satisfy the condition of destructive interference with respect to a wavelength destructively interfered by the first cladding layer 171.

[0140] As shown in a region B, a reflective anode 1100 having a three-layer structure formed by stacking the transparent electrodes 112a and 112b below and above a reflective electrode 111, an organic light-emitting diode OLED including a first common hole-transport layer 131, an organic light-emitting layer 132, a second common electron-transport layer 133, a third common electron-injection layer 134, and a transmissive electrode 140 provided as a thin transflective or transparent electrode formed of silver or a silver alloy, which are stacked in sequence above the reflective anode 1100, and the above-described cap structure 170 including the first cap layer 171 and the second cap layer 172 formed above the organic light-emitting diode OLED are provided in the emission section E.

[0141] The transparent electrode 1200 of the transmission section T may include only one of the upper and lower transparent electrodes 112b and 112a, while the reflective anode 1200 of the emission section E may include one or both of the upper and lower transparent electrodes 112b and 112a with the reflective electrode 111. In some cases, the transparent electrode 1200 of the transmission section T may include both the upper and lower transparent electrodes 112b and 112a.

[0142] In the present invention, the wavelength of the emitted red light is in the range of 600 nm to 650 nm, the wavelength of the emitted blue light is in the range of 430 nm to 460 nm, and the wavelength of the emitted green light is in the range of 510 nm to 590 nm. That is, the red sub-pixels RE, the blue sub-pixels BE, and the green sub-pixels GE emit light of different colors.

[0143] In a Fig.In the example illustrated in FIG. 14, one pixel may include the red, green, and blue sub-pixels RE, GE, and BE adjacent to each other in the vertical direction, and three transmission portions T adjacent to the red, green, and blue sub-pixels RE, GE, and BE, respectively. A plurality of pixels may be arranged in a matrix above the transparent substrate 100. The respective emission portions E and transmission portions T are connected to the first thin-film transistors TFT1 and the second thin-film transistors TFT2, and thus may operate as sub-pixels that are independently driven. Although the example illustrates that the transparent electrode 1200 is provided in the transmission portion T, and thus the transmission portion T may be driven by the second thin-film transistor TFTS, the transparent electrode 1200 and the second thin-film transistor TFTS may be omitted from the transmission portion T.If the second thin film transistor TFTS is provided for the pass section T as shown in . Fig. 14 and Fig. As shown in Figure 15, the transmission portion T can be selectively driven as needed. In this case, a light-emitting layer may be further provided in the transmission portion T to add the light-emitting characteristics according to the selective driving.

[0144] The transparent electrode 1200 of the transmission section T may be provided by leaving only the transparent electrode layer under the reflective anode 1100 provided in the emission section E.

[0145] A red organic light-emitting layer 132 is provided in each red sub-pixel RE, a blue organic light-emitting layer 132 is provided in each blue sub-pixel BE, and a green organic light-emitting layer 132 is provided in each green sub-pixel GE.

[0146] The first thin-film transistor TFT1 in the emission section E includes a first gate electrode 1120 formed in the same layer as the scan lines SL, a first semiconductor layer 1110 provided with a channel region overlapping the first gate electrode 1120, and a first source electrode 1140 and a first drain electrode 1160 connected to both sides of the first semiconductor layer 1110. Further, the first gate electrode 1120 may be formed as a projection pattern protruding from the scan line SL and integrally formed with the scan line SL. The first source electrode 1140 may be formed as a projection pattern protruding from the data line DL, wherein the first drain electrode 1160 is spaced apart from the first source electrode 1140 and connected to the reflective anode 1100 of the organic light-emitting diode (OLED) through a first connection portion CT1.

[0147] The second thin-film transistor TFTS can be formed by the same process as the first thin-film transistor TFT1 and thus includes a second gate electrode 1122 formed in the same layer as the scan lines SL, a second semiconductor layer 1112 provided with a channel region overlapping the second gate electrode 1122, and a second source electrode 1161 and a second drain electrode 1142 connected to both sides of the second semiconductor layer 1112. Further, the second gate electrode 1122 can be formed as a projection pattern protruding from the scan line SL and integrally formed with the scan line SL, or as a projection pattern protruding from another scan line ASL (not shown) that is separately provided.Here, if the second gate electrode 1122 is formed from or connected to the separate scanning line ASL, the second thin-film transistor TFT1 may attempt to be driven at a different timing than the first thin-film transistor TFT1. The second source electrode 1161 may be formed as a protrusion pattern protruding from the data line DL, in which case, the data line DL to which the second source electrode 1161 is connected may be a different data line DL from the data line DL to which the first thin-film transistor TFT1 is connected. Further, the second drain electrode 1142 is spaced apart from the data line DL and the second source electrode 1161, and the second drain electrode 1142 is connected to the transparent electrode 1200 of the transmission portion T through a second connection portion CT2.

[0148] The layered structure of the transparent display device is Fig. 15 is described in detail as follows.

[0149] A buffer layer 105 is provided above the transparent substrate 100, with first, second, and third semiconductor layers 1110, 1112, and 1111 being provided above the buffer layer 105. The buffer layer 105 serves to prevent impurities remaining in the transparent substrate 100 from being introduced into the semiconductor layers 1110, 1112, and 1111. The semiconductor layers 1110, 1112, and 1111 may be amorphous or crystalline silicon semiconductor layers or transparent oxide semiconductor layers. Further, the two sides of the first and second semiconductor layers 1110 and 1112 connected to the first and second source electrodes 1140 and 1161 and the first and second drain electrodes 1160 and 1142 may be regions into which the impurities are injected, and the intrinsic regions of the first and second semiconductor layers 1110 and 1112 between the regions into which the impurities are injected may function as the channel regions.

[0150] The third semiconductor layer 1111 may be arranged to overlap the storage electrodes 1121 and 1141 formed thereon and used as an auxiliary storage electrode that increases the capacitance of a storage capacitor STC when impurities are injected. Otherwise, the third semiconductor layer 1111 may be omitted as required by circumstances.

[0151] Further, a gate insulating film 106 is provided overlying the first to third semiconductor layers 1110, 1112, and 1111, and the first and second gate electrodes 1120 and 1122 and the first storage electrode 1121 are formed, which overlap the intrinsic regions of the first and second semiconductor layers 1110 and 1112, and the third semiconductor layer 1111, respectively.

[0152] A first interlayer insulating film 107 is provided to overlie the first, second, and third semiconductor layers 1110, 1112, and 1111, the first and second gate electrodes 1120 and 1122, and the first storage electrode 1121.

[0153] By selectively removing the first interlayer insulating film 107 and the gate insulating film 106 from both sides of the first semiconductor layer 1110 and the second semiconductor layer 1112, contact holes are formed, through which the first source electrode 1140 and the first drain electrode 1160 are connected to the first semiconductor layer 1110, and the second source electrode 1161 and the second drain electrode 1142 are connected to the second semiconductor layer 1112. In the same process, the second storage electrode 1141 is formed over the first interlayer insulating film 107, overlapping the first storage electrode 1121.

[0154] Here, the first thin-film transistor TFT1 for driving the first organic light-emitting diode (OLED) provided in the emission section E includes the first semiconductor layer 1110, the first gate electrode 1120 provided with the channel region overlapping the first semiconductor layer 1110, and the first source electrode 1140 and the first drain electrode 1160 connected to both sides of the first semiconductor layer 1110, which are stacked sequentially from the bottom. The second thin-film transistor TFT1 for driving a second organic light-emitting diode provided in the transmission section T does not overlap the transmission section T and has the same layered structure as the first thin-film transistor TFT1, i.e., it includes the second semiconductor layer 1112, the second gate electrode 1122 provided with the channel region overlapping the second semiconductor layer 1112, and the second source electrode 1161 and the second drain electrode 1142 connected to the both sides of the second semiconductor layer 1112, which are stacked in order from the bottom.

[0155] Further, the storage capacitor STC includes the first and second storage electrodes 1121 and 1141 overlapping each other with the first interlayer insulating film 107 interposed therebetween.

[0156] A second interlayer insulating film 108 is formed to overlay the first and second thin film transistors TFT1 and TFTS and the storage capacitor STC.

[0157] Here, the first and second thin-film transistors TFT1 and TFTS and the storage capacitor STC include light-shielding metal layers, and are arranged so as not to overlap the transmission section T. Consequently, the first and second thin-film transistors TFT1 and TFTS may be arranged so as to overlap the emission section or a region for forming the bank 150. Here, the bank 150 may be located between the transmission section T and the emission section E, or may be located between the emission regions of the emission sections E that are spaced apart from each other. In the emission section E, the reflective anode 1100 allows the metal layers arranged thereunder to be invisible, and in a region where the bank 50 is located, the thick bank 50 allows the elements arranged thereunder to be invisible.

[0158] Further, a planarization film 109 may be formed to planarize the surface of the second interlayer insulating film 108 while overlying the second interlayer insulating film 108, wherein the first and second connecting portions CT1 and CT2 may be formed by selectively removing the planarization film 109 and the second interlayer insulating film 108, while the first and second thin film transistors TFT1 and TFT2 may be connected to the reflective anode 1100 and the transparent electrode 1200 through the first and second connecting portions CT1 and CT2.

[0159] The transparent display device according to the present invention may further include a barrier rib 160 in certain areas of the sections where the transmission sections T and the emission sections E are not located, wherein the barrier rib 160 may separate the adjacent transmission sections T or emission sections E. The barrier rib 160 prevents a deposition mask (not shown) used for the deposition of an organic material when the organic stacks 130 and 130' are formed from being in direct contact with the bank 150, thus maintaining the shape of the bank 150 without the bank 150 collapsing.

[0160] The barrier rib 160 includes a first layer 161 formed in the same layer as the bank 150, and a second layer 162 located a certain height from the top of the first layer 161 so as to overlie the first layer 161. To prevent the deposition mask required to form the organic common layer or the light-emitting layer from being in direct contact with the bank 150 or from sagging after the bank 150 is formed, the second layer 162 may be formed in the same layer as a spacer (not shown) formed above the bank 150. An encapsulation layer 300 is formed over the capping structure 170.

[0161] In the emission section E, the reflective anode 1100 and the transmissive electrode 140 are arranged opposite each other. Here, the reflective anode 1100 is illustrated as having a three-layer structure including the reflective electrode layer 111 and the upper and lower transparent electrode layers 112b and 112a, but is not limited thereto. That is, one or both of the transparent electrode layers 112b and 112a may be omitted, or a plurality of transparent electrode layers 112b and 112a and a plurality of reflective electrode layers 111 may be provided. If the reflective anode 1100 includes at least one transparent electrode layer, the transparent electrode 1200 in the transmission section T may be formed by the same process as the transparent electrode layer.In addition, the transparent electrode 140 is in contact with an auxiliary electrode 1300, which is located in the same layer as the reflective anode 1100. The auxiliary electrode 130 is spaced apart from the reflective anode 1100.

[0162] Although the above-described example describes the organic light-emitting diode OLED provided in the emitting section E as a single stack including a single organic light-emitting layer in each sub-pixel, an organic light-emitting diode including multiple stacks each including a light-emitting layer is applicable to the transparent display device according to the present invention.

[0163] Fig. 16 is a cross-sectional view illustrating a transparent display device according to a third embodiment of the present invention.

[0164] As in Fig.As shown in Fig. 16, the transparent display device according to the third embodiment of the present invention is divided into the emission sections E and the transmission sections T. In a subpixel of each emission section E, above a substrate 200 containing thin-film transistors, a reflective anode 1100 connected to each thin-film transistor is provided, an organic stack including a hole injection layer 231, a first hole transport layer 232, a first organic light emission layer 233a, 233b or 233c, a first electron transport layer 234, a charge generation layer 235 formed by stacking an n-type charge generation layer (nCGL) 235a and a p-type charge generation layer (pCGL) 235b, a second hole transport layer 236, a second organic light emission layer 237a, 237b and 237c, a second electron transport layer 238 and an electron injection layer 239,which are stacked in sequence above the reflective anode 1100, and a transmissive electrode 240 with transflective properties and a small thickness is provided above the organic stack, thereby forming an organic light-emitting diode.

[0165] Although this embodiment illustrates that the organic stack is a two-stack structure divided into a first stack located in a lower region and a second stack located in an upper region based on the charge generation layer 235, the organic stack is not limited thereto, and one or more stacks each including a hole transport layer, an organic light emission layer, and an electron transport layer may be further provided above the second electron transport layer 238.

[0166] Furthermore, this embodiment describes an example in which the organic light-emitting layers emitting light of the same color are deposited on the respective stacks to improve the color efficiencies of the red, green, and blue light.

[0167] Further, the first organic light-emitting layers 233a, 233b, and 233c and the second organic light-emitting layers 237a, 237b, and 237c, which emit light of the respective colors, are set to have different thicknesses to achieve optimal resonance of the light of the respective colors.

[0168] In the transmission portion T provided adjacent to the emission portion E, the hole injection layer 231, the first electron transport layer 234, the charge generation layer 235 formed by stacking the n-type charge generation layer (nCGL) 235a and the p-type charge generation layer (pCGL) 235b, the second hole transport layer 236, the second electron transport layer 238, and the electron injection layer 239 are stacked as common elements of an organic stack.

[0169] Furthermore, the transmissive electrode 240 and a cap structure 270 formed by stacking a first cap layer 271 having a high refractive index and destructive interference properties and a second cap layer 272 having a low refractive index are jointly deposited on the organic stacks in the emission section E and the transmission section T.

[0170] As described above, the capping structure 270 is characterized in that a refractive index difference at the interface between the respective capping layers 271 and 272 is small, a refractive index difference at the interface between the upper surface of the second capping layer 272 and an encapsulation layer outside the second capping layer 272 is small, and thus, an amount of light transmitted through the capping structure 270 can be increased due to the antireflection effect by the low reflectances of the respective interfaces. Furthermore, the color efficiency can be improved by the destructive interference properties without distorting the color coordinates.

[0171] Although the above-described embodiments depict the capping structure as a two-layer structure including the first and second capping layers, the capping structure is not limited to this and may have a three-layer or more structure. However, the capping structure is provided over the transmissive electrode in the transmission portion and has a total thickness of 200.0 nm or less, taking light shielding into account.

[0172] The light emitted by the organic light-emitting diode OLED is transmitted sequentially through the transmissive electrode, the first cap layer, and the second cap layer, wherein an amount of light transmitted through the second cap layer may be proportional to a value obtained by subtracting the reflectance of the transmissive electrode, the reflectance of the interface between the first cap layer and the second cap layer, and the reflectance of the top surface of the second cap layer from 1, assuming that the total amount of light emitted by the organic light-emitting diode is 1.

[0173] In the transparent display device of the present invention, the two different emission portions may be adjacent to a transmission portion.

[0174] In addition, a transmission section can be surrounded by four emission sections.

[0175] Furthermore, the shape of the passage section can be hexagonal or diamond-shaped.

[0176] In addition, two green emission sections, one red emission section and one blue emission section can surround each transmission section.

[0177] The red or blue emission sections can correspond diagonally to the green emission section with the transmission section in between.

[0178] In the present invention, the TFT may be overlapped with the emission portion outside the transmission portion.

[0179] In addition, the permeable electrode can be connected to an auxiliary electrode (see 1300 after Fig. 15), which is located in the same layer as the anode.

[0180] The transparent display device of the present invention may further comprise a bank to define the emitting portion and the transmitting portion, and a spacer on the bank, wherein the bank has a positive taper and the spacer has a negative taper.

[0181] Furthermore, a transparent display device according to another embodiment may comprise: a reflective electrode structure over a substrate, an organic light-emitting layer over the reflective electrode structure, a transmissive electrode over the organic light-emitting layer, and a cap structure comprising a first cap layer over the transmissive electrode having destructive interference properties and a first refractive index, and a second cap layer having a second refractive index smaller than the first refractive index over the first cap layer.

[0182] Furthermore, the transparent display device according to another embodiment has the following features, such that the substrate has a plurality of pixels, an emitting portion and a transmitting portion are located in each of the pixels, the reflective electrode structure is located between the organic light-emitting layer and the substrate in the emitting portion, and the capping structure is located over the emitting portion and the transmitting portion throughout the pixels over the substrate and the second capping layer.

[0183] As is obvious from the above description, a transparent display device according to the present invention has the effects as follows.

[0184] First, a capping structure formed by stacking a first capping layer having a high refractive index and destructive interference characteristics and a second capping layer having a low refractive index is jointly deposited on the emitting portions and the transmitting portions, and consequently, a refractive index difference at the interface between the respective capping layers is small, a refractive index difference at the interface between the top surface of the second capping layer and an encapsulation layer outside the second capping layer is small, and thereby an amount of light transmitted through the capping layer structure can be increased due to the antireflection effect by the low reflectances of the respective interfaces.

[0185] Secondly, the interference effect of the two-layer cover structure is optimized and the first and second cover layers have the same or similar optical path lengths, and consequently the color efficiency can be improved due to the increase in transmittance by the destructive interference with respect to the wavelengths in similar ranges without distortion of the color coordinates.

[0186] Third, by changing the thickness of a second electrode and the structure of the cover structure, a transparent light-emitting diode with high efficiency can be implemented without changing the internal configuration of the light-emitting diode.

[0187] Fourth, a high transmittance of the transmission portion can be ensured and an EL spectrum of the emission portion can be optimized.

[0188] Fifth, uniform transmittance in the visible wavelength range can be ensured.

Claims

[1] Transparent display device comprising: a substrate (100) having a plurality of pixels (P); at least one emission section (E) and at least one transmission section (T) in each of the pixels (P); an organic light-emitting layer (132a, 132b, 132c) in the emitting section (E); a reflective electrode structure (111) between the organic light-emitting layer (132a, 132b, 132c) and the substrate in the emission section (E); a transmissive electrode (140) located above the emitting portion (E) and the transmitting portion (T) throughout the pixels (P) above the substrate (100); a capping structure (170) comprising a first capping layer (171) over the transmissive electrode (140) having the properties of destructive interference and a first refractive index n1, and a second capping layer (172) configured over the first capping layer (171) and having a second refractive index n2 that is smaller than the first refractive index n1; and an encapsulation layer (300); wherein light reflected downward at an interface between the transmissive electrode (140) and the cover structure (170) and light reflected downward at an interface between the cover structure (170) and the encapsulation layer (300) have opposite phases. [2] The transparent display device according to claim 1, wherein the first refractive index is 2.0 or greater and the second refractive index is 0.2 to 1.2 smaller than the first refractive index, preferably the first refractive index is 2.0 to 2.7 and the second refractive index is 1.3 to 2.

0. [3] Transparent display device according to one of claims 1 or 2, wherein: the first cover layer (171) has a first thickness d1; and a first optical path length n1d1 of the first cover layer (171) has a value of mλ / 2cosθ, where m is an integer, λ is a wavelength of destructive interference and θ is an angle of incidence and / or the second cover layer (172) has a second thickness d2; and / or a second optical path length n2d2 of the second cover layer (172) is 0.9 to 1.1 times the first optical path length n1d1. [4] The transparent display device according to claim 3, wherein the destructive interference wavelength is a blue wavelength or a deep blue wavelength, and / or wherein a peak wavelength of the destructive interference wavelength is in the range of 430 nm to 465 nm. [5] A transparent display device according to any one of the preceding claims, wherein a difference between the reflectance of an upper surface of the second cover layer (172) and the reflectance of an interface between the first cover layer (171) and the second cover layer (172) is within 5%. [6] A transparent display device according to any one of the preceding claims, further comprising the encapsulation layer (300) over the second cover layer (172), and wherein the reflectance of a top surface of the second cover layer (172) (n2 cosθi−nEncap cosθtn2 cosθi+nEncap cosθt)2 is, where n Encapis a refractive index of the encapsulation layer (300), θ i is an angle of incidence and θ t is an exit angle. [7] A transparent display device according to claim 6, wherein the reflectance of an interface between the first cover layer (171) and the second cover layer (172) (n1 cosθi−n2 cosθtn1 cosθi+n2 cosθt)2 wherein a difference between the reflectance of the interface between the first cover layer (171) and the second cover layer (172) and the reflectance of the top surface of the second cover layer (172) is 5% or less. [8] Transparent display device according to claim 3, wherein: the first thickness is 25.0 nm to 50.0 nm; and / or the second thickness is 30.0 nm to 70.0 nm and / or the permeable electrode (140) is formed from a silver alloy, and / or the thickness of the permeable electrode (140) is 5.0 nm to 10.0 nm. [9] A transparent display device according to any one of the preceding claims, wherein: the light emitted through an upper surface of the organic light-emitting layer (132a, 132b, 132c) is transmitted sequentially through the transmissive electrode (140), the first cap layer (171), and the second cap layer (172); and an amount of light transmitted through the second cap layer (172) is 1-R, where R is an amount of light reflected by the cap structure (170) and is close to 0. [10] A transparent display device according to any one of the preceding claims, wherein the organic light-emitting layer (132a, 132b, 132c) is further provided in the transmission portion (T), and the organic light-emitting layer (132a, 132b, 132c) in the transmission portion (T) operates as a sub-pixel independently driven with the organic light-emitting layer (132a, 132b, 132c) in the emission portion (E). [11] Transparent display device according to one of the preceding claims, wherein the cover structure (170) is provided as a three-layer or a four-layer cover structure; wherein the refractive indices of the respective cover layers gradually decrease in the upward direction; wherein the lowest cover layer has the properties of destructive interference and the optical path lengths of the other cover layers are each 0.9 to 1.1 times the optical path length of the lowest cover layer; and where the reflectance difference between the respective interfaces of the respective cover layers is 5% or less. [12] Transparent display device according to one of the preceding claims, wherein two different emission sections (RE, BE) are adjacent to a transmission section (T) and / or wherein a transmission section (T) is surrounded by four emission sections (RE, BE, GE, GE), and / or wherein a shape of the transmission section (T) is hexagonal or diamond-shaped; and / or two green emission sections (GE), one red emission section (RE) and one blue emission section (BE) surround each transmission section (T) and / or wherein the red or blue emission sections (RE, BE) correspond diagonally to the green emission section (GE) with a transmission section (T) therebetween. [13] A transparent display device according to any one of the preceding claims, wherein a TFT is overlapped with the emitting portion (E) outside the transmitting portion (T) and / or wherein the transmitting electrode (140) is in contact with an auxiliary electrode (1300) located in the same layer as the reflecting electrode (111, 1100). [14] A transparent display device according to any one of the preceding claims, further comprising a bank (150) to define the emitting section (E) and the transmitting section (T), and a spacer on the bank (150), the bank (150) having a positive taper and the spacer having a negative taper. [15] Transparent display device comprising: the reflective electrode (111, 1100) is located. a transparent electrode (140) over the organic light-emitting layer (132); a cover structure (170) comprising a first cover layer (171) over the transmissive electrode (140) having the properties of destructive interference and a first refractive index, and a second cover layer (172) having a second refractive index that is smaller than the first refractive index over the first cover layer; and an encapsulation layer (300); wherein light reflected downward at an interface between the transmissive electrode (140) and the cover structure (170) and light reflected downward at an interface between the cover structure (170) and the encapsulation layer (300) have opposite phases. [16] Transparent display device according to claim 15, wherein the substrate (100) has a plurality of pixels (P), each of the pixels including an emission section (E) and a transmission section (T); wherein the reflective electrode structure (1100) is located between the organic light emission layer (132) and the substrate (100) in the emission section (E), and wherein the capping structure (170) is located over the emitting portion (E) and the transmitting portion (T) throughout the pixels (P) over the substrate (100) and the second capping layer (172).

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